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Microscope
Optical microscope nikon alphaphot +.jpg
Uses Small sample observation
Notable experiments
Discovery of cells
Inventor Hans Lippershey
Zacharias Janssen
Related items Electron microscope
A microscope (from the Greek: μικρός, mikrós, "small" and σκοπεῖν, skopeîn, "to look" or "see") is an instrument to see objects too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy. Microscopic means invisible to the eye unless aided by a microscope.

Contents

History

An early microscope was made in 1590 in Middelburg, The Netherlands.[1] Three eyeglass makers are variously given credit: Hans Lippershey (who developed an early telescope); Zacharias Jansen, with the help of his father, Hans Janssen. Giovanni Faber coined the name for Galileo Galilei's compound microscope in 1625.[2] (Galileo had called it the "occhiolino" or "little eye".)
The first detailed account of the interior construction of living tissue based on the use of a microscope did not appear until 1644, in Giambattista Odierna's L'ochio della mosca, or The Fly's Eye. [3]
It was not until the 1660s and 1670s that the microscope was used seriously in Italy, Holland and England. Marcelo Malpighi in Italy began the analysis of biological structures beginning with the lungs. Robert Hooke's Micrographia had a huge impact, largely because of its impressive illustrations. The greatest contribution came from Antoni van Leeuwenhoek who discovered red blood cells and spermatozoa. On 9 October 1676, Leeuwenhoek reported the discovery of micro-organisms.[4]
The most common type of microscope—and the first invented—is the optical microscope. This is an optical instrument containing one or more lenses producing an enlarged image of an object placed in the focal plane of the lenses.

Types

Types of microscopes
"Microscopes" can be separated into optical theory microscopes (Light microscope), electron microscopes (e.g.,TEM), and scanning probe microscopes (SPM). Optical microscopes function through the optical theory of lenses in order to magnify the image generated by the passage of a wave through the sample, or reflected by the sample. The waves used are electromagnetic (in optical microscopes) or electron beams (in electron microscopes). Types are the compound light, stereo, and the electronic microscope.
Optical microscopes, using visible wavelengths of light, are the simplest and most used. Optical microscopes have refractive glass and occasionally of plastic or quartz, to focus light into the eye or another light detector. Mirror-based optical microscopes operate in the same manner. Typical magnification of a light microscope, assuming visible range light, is up to 1500x with a theoretical resolution limit of around 0.2 micrometres or 200 nanometers. Specialized techniques (e.g., scanning confocal microscopy, Vertico SMI) may exceed this magnification but the resolution is diffraction limited. The use of shorter wavelengths of light, such as the ultraviolet, is one way to improve the spatial resolution of the optical microscope, as are devices such as the near-field scanning optical microscope.
Sarfus, a recent optical technique increases the sensitivity of standard optical microscope to a point it becomes possible to directly visualize nanometric films (down to 0.3 nanometer) and isolated nano-objects (down to 2 nm-diameter). The technique is based on the use of non-reflecting substrates for cross-polarized reflected light microscopy.
Ultraviolet light enables the resolution of microscopic features, as well as to image samples that are transparent to the eye. Near infrared light images circuitry embedded in bonded silicon devices, as silicon is transparent in this region. Many wavelengths of light, ranging from the ultraviolet to the visible are used to excite fluorescence emission from objects for viewing by eye or with sensitive cameras.
Phase contrast microscopy is an optical microscopy illumination technique in which small phase shifts in the light passing through a transparent specimen are converted into amplitude or contrast changes in the image. A phase contrast microscope does not require staining to view the slide. This microscope made it possible to study the cell cycle.
The traditional optical microscope has been recently modified into a digital microscope, where instead of directly viewing the object, a charge-coupled device (CCD) camera projects the image to a monitor.

Electron microscopes


Three major variants of electron microscopes exist:
The SEM and STM can also be considered examples of scanning probe microscopy.

Established types of scanning probe microscopy

Of these techniques AFM and STM are the most commonly used followed by MFM and SNOM/NSOM.

Other microscopes

Replica of microscope by Van Leeuwenhoek
Different microscopes
Scanning acoustic microscopes use sound waves to measure variations in acoustic impedance. Similar to Sonar in principle, they are used for such jobs as detecting defects in the subsurfaces of materials including those found in integrated circuits.

See also

References

  1. ^ Microscopes: Time Line
  2. ^ Stephen Jay Gould(2000). The Lying Stones of Marrakech, ch.2 "The Sharp-Eyed Lynx, Outfoxed by ature". London: Jonathon Cape. ISBN 0224050443
  3. ^ Bad Medicine: Doctors doing harm since Hippocrates. David Wootton. Oxford University Press, 2006.
  4. ^ see Wootton, David (2006) p. 119.
  5. ^ Morita, Seizo. Roadmap of Scanning Probe Microscopy. 3 January 2007

External links


Study guide

Up to date as of January 14, 2010

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Resources


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

MICROSCOPE (Gr. .yucpos, small,;view), an optical instrument for examining small objects or details of such objects; it acts by making the angles of vision under which the images appear greater than when the objects themselves are viewed by the naked eye.^ The greater the visual angle, the more distinctly are the details of the object perceived.

^ Therefore we can assume that a detail which appears under an angle of 2' can be surely perceived.

^ The image vector is at an angle 180° + q to the object vector.

.Microscopes are distinguished as simple and compound. A simple microscope consists of a single positive lens, or of a lens combination acting as a single lens, placed between the eye and the object so that it presents a virtual and enlarged image.^ Microscopes are distinguished as simple and compound.

^ An object placed anywhere to the left of a diverging lens results in an erect virtual image.

^ A simple microscope consists of a single positive lens , or of a lens combination acting as a single lens, placed between the eye and the object so that it presents a virtual and enlarged image .

.The compound microscope generally consists of two positive lens systems, so arranged that the system nearer the object (termed the objective) projects a real enlarged image, which occupies the same place relatively to the second system (the eyepiece or ocular) as does the real object in the simple microscope.^ Microscopes are distinguished as simple and compound.

^ A microscope is essentially formed by two lenses: the objective and the eyepiece which is also referred to as the ocular.
  • A one Dollar Compound Microscope 23 January 2010 9:54 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ The compound microscope generally consists of two positive lens systems, so arranged that the system nearer the object (termed the objective ) projects a real enlarged image, which occupies the same place relatively to the second system (the eyepiece or ocular ) as does the real object in the simple microscope.

.An image is therefore projected by the ocular from the real magnified image produced by the objective with increased magnification.^ An image is therefore projected by the ocular from the real magnified image produced by the objective with increased magnification.

^ The image produced by an objective lens is conjugate with the specimen, meaning that each image point at the intermediate plane is geometrically related to a corresponding point in the specimen.
  • Molecular Expressions: Images from the Microscope 1 February 2010 1:54 UTC microscope.fsu.edu [Source type: FILTERED WITH BAYES]

^ I.30-I.32) In principle, a real image of any desired magnification can be obtained from a single positive lens, but in practice this is cumbersome because of the long lens-image distance.

Table of contents

History of the Simple Microscope

.Any solid or liquid transparent medium of lenticular form, having either one convex and one flat surface or two convex surfaces whose axes are coincident, may serve as a " magnifier," the essential condition being that it shall refract the rays which pass through it so as to cause widely diverging rays to become either parallel or but slightly divergent.^ C and D are the outermost rays which can pass through the instrument.

^ Any solid or liquid transparent medium of lenticular form, having either one convex and one flat surface or two convex surfaces whose axes are coincident, may serve as a " magnifier," the essential condition being that it shall refract the rays which pass through it so as to cause widely diverging rays to become either parallel or but slightly divergent.

^ The thin wall 12 is electron-transparent, i.e., electron beams may be passed through it without significant dispersion or attenuation, relative to the intended application.
  • Tip for Nanoscanning Electron Microscope - US Patent # 6,943,356 1 February 2010 1:54 UTC www.biomedsolutions.com [Source type: Reference]

.Thus if a minute object be placed on a slip of glass, and a single drop of water be placed upon it, the drop will act as a magnifier in virtue of the convexity of its upper surface; so that when the eye is brought sufficiently near it (the glass being held horizontally) the object will be seen magnified.^ Thus if a minute object be placed on a slip of glass , and a single drop of water be placed upon it, the drop will act as a magnifier in virtue of the convexity of its upper surface; so that when the eye is brought sufficiently near it (the glass being held horizontally) the object will be seen magnified.

^ A convex lens of rockcrystal was found by Layard among the ruins of the palace of Nimrud; Seneca describes hollow spheres of glass filled with water as being commonly used as magnifiers.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

.Again if a small hole be made in a thin plate of metal, and a minute drop of water be inserted in it, this drop, having two convex surfaces, will serve as a still more powerful magnifier.^ Again if a small hole be made in a thin plate of metal , and a minute drop of water be inserted in it, this drop, having two convex surfaces, will serve as a still more powerful magnifier.

^ The more strongly curved surface is placed next the eye, the other serves at the same time as specimen carrier .

^ When the holes are small, it may be easy to form a film but it is difficult to obtain a thin film.
  • Cryogenic Transmission Electron Microscope 1 February 2010 1:54 UTC www.jeoleuro.com [Source type: Academic]

.There is reason to believe that the magnifying power of transparent media with convex surfaces was very early known.^ There is reason to believe that the magnifying power of transparent media with convex surfaces was very early known.

^ These electrons are generated within very small depth ( < 2 nm) below the surface, known as the escape depth .
  • PHYS 319: The Scanning Electron Microscope 1 February 2010 1:54 UTC laser.phys.ualberta.ca [Source type: Reference]

^ Supposing, however, there is oblique illumination, then formula (5) can always be applied to determine the magnifying power attainable with at least one objective.

.A convex lens of rockcrystal was found by Layard among the ruins of the palace of Nimrud; Seneca describes hollow spheres of glass filled with water as being commonly used as magnifiers.^ A convex lens of rockcrystal was found by Layard among the ruins of the palace of Nimrud; Seneca describes hollow spheres of glass filled with water as being commonly used as magnifiers.

^ If possible use a plano-convex lens).
  • A one Dollar Compound Microscope 23 January 2010 9:54 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ Composite maps created by overlaying the images are commonly used for the characterization of region patterns in materials such as: glass, mineral, and concrete.
  • ASPEX Personal Scanning Electron Microscope Solutions 1 February 2010 1:54 UTC aspexcorp.com [Source type: FILTERED WITH BAYES]

.The perfect gem-cutting of the ancients could not have been attained without the use of magnifiers; and doubtless the artificers who executed these wonderful works also made them.^ The perfect gem -cutting of the ancients could not have been attained without the use of magnifiers; and doubtless the artificers who executed these wonderful works also made them.

^ These pictures were made of a test device without a biological sample.
  • PLoS ONE: Nanoscale Imaging of Whole Cells Using a Liquid Enclosure and a Scanning Transmission Electron Microscope 1 February 2010 1:54 UTC www.plosone.org [Source type: Academic]

^ It is clear that these approaches work in some instances and may therefore be used to provide a coarse alignment, but an approach that truly considers the shape of the contours is required.

.Convex glass lenses were first generally used to assist ordinary vision as " spectacles "; and not only were spectacle-makers the first to produce glass magnifiers (or simple microscopes), but by them also the telescope and the compound microscope were first invented.^ Microscopes are distinguished as simple and compound.

^ A combination microscope, telescope, and magnifying glass.

^ A simple microscope with interchangeable lenses.

.During the Thirty Years' War the simple microscope was widely known.^ During the Thirty Years' War the simple microscope was widely known.

.Descartes (Dioptrique, 1637) describes microscopes wherein a concave mirror, with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.^ The mirror is used to illuminate the specimen from underneath.
  • A one Dollar Compound Microscope 23 January 2010 9:54 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ A microscope, using concave mirrors, was proposed in 1672 by Sir Isaac Newton ; and he was succeeded by Barker, R. Smith, B. Martin , D. Brewster, and, above all, Amici.

.Antony van Leeuwenhoek appears to be the first to succeed in grinding and polishing lenses of such short focus and perfect figure as to render the simple microscope a better instrument for most purposes than any compound microscope then constructed.^ Microscopes are distinguished as simple and compound.

^ Only in the first half of the 1800's were compound microscopes perfected.
  • Glass-sphere microscope 23 January 2010 9:54 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ Antony van Leeuwenhoek appears to be the first to succeed in grinding and polishing lenses of such short focus and perfect figure as to render the simple microscope a better instrument for most purposes than any compound microscope then constructed.

.At that time the " compass " microscope was in use.^ At that time the " compass " microscope was in use.

^ Microscopes with significant field curvature are difficult to use, especially for extended periods of time in which the operator must be continuously refocusing the specimen to examine the entire field.
  • Nikon MicroscopyU | Concepts and Formulas in Microscopy: Basic Microscope Ergonomics 23 January 2010 9:54 UTC www.microscopyu.com [Source type: FILTERED WITH BAYES]

.One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw.^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

.Stands were also in use, permitting the manipulation of the object by hand.^ Stands were also in use, permitting the manipulation of the object by hand.

^ In cheap stands the rough adjustment was worked by moving the inner tube by hand, but the more convenient rack and pinion is now used almost exclusively.

^ Where very short focus simple microscopes are employed, using high magnifications, it is imperative to employ a stand which permits exact focusing and the use of a special illuminating apparatus.

.Robert Hooke shaped the minutest of the lenses with which he made many of the discoveries recorded in his Micrographia from small glass globules made by fusing the ends of threads of spun glass; and the same method was employed by the Italian Father Di Torre.^ Robert Hooke shaped the minutest of the lenses with which he made many of the discoveries recorded in his Micrographia from small glass globules made by fusing the ends of threads of spun glass; and the same method was employed by the Italian Father Di Torre.

^ The arrangement of two lenses so that small objects can be seen magnified followed soon after the discovery of the telescope.

^ These two conditions are only compatible when the representation is made with quite narrow pencils, and where the apertures are so small that the sines and tangents are of about the same value.

.Early opticians and microscopists gave their chief attention to the improvement of the simple microscope, the principle of which we now explain.^ Early opticians and microscopists gave their chief attention to the improvement of the simple microscope, the principle of which we now explain.

^ Microscopes have undergone a remarkable evolution since their invention in the early 1600s, but most of the new developments and improvements have been in the area of contrast enhancement accessories and the microscope optical train.
  • Nikon MicroscopyU | Concepts and Formulas in Microscopy: Basic Microscope Ergonomics 23 January 2010 9:54 UTC www.microscopyu.com [Source type: FILTERED WITH BAYES]

^ Compound Microscope The view held by early opticians, that a compound microscope could never produce such good images as an instrument of the simple type, has proved erroneous; and the principal attention of modern opticians has been directed to the compound instrument.

.Simple Microscope Position and Size of the Image.^ Obviously, the performance of this simple microscope cannot be compared with more expensive professional instruments, which will produce much clearer and brighter images.
  • A one Dollar Compound Microscope 23 January 2010 9:54 UTC www.funsci.com [Source type: FILTERED WITH BAYES]

^ Since H' P = F 0, = y, from the focal length of the simple microscope, the visual angle w' is given by tan w'/y=I/f'=V, (I) in which f', = H' F', is the image-side focal length (see Lens ).

^ The simple microscope enlarges the angle of vision, and does not tire the eye when it is arranged so that the image lies in the farthest limit of distinct vision (the punctum remotum).

- .A
person with normal vision can see objects distinctly at a distance varying from ten inches to a very great distance.^ A person with normal vision can see objects distinctly at a distance varying from ten inches to a very great distance.

^ A normal eye will therefore see an image formed by the magnifying glass most conveniently when it is produced at a great distance, i.e.

^ Objects at different distances, however, are not seen distinctly simultaneously, but in succession.

.Objects at different distances, however, are not seen distinctly simultaneously, but in succession.^ Objects at different distances, however, are not seen distinctly simultaneously, but in succession.

^ This is effected by the power of accommodation of the eye, which can so alter the focal length of its crystalline lens that images of objects at different distances can be produced rapidly and distinctly one after another upon the retina.

^ Owing to the curvature of the image, all parts of the object are not seen distinctly at one and the same time.

.This is effected by the power of accommodation of the eye, which can so alter the focal length of its crystalline lens that images of objects at different distances can be produced rapidly and distinctly one after another upon the retina.^ Let f = lens focal length, x o = distance of object in front of the lens, and x i = distance of image behind the lens.

^ Objects at different distances, however, are not seen distinctly simultaneously, but in succession.

^ When the object distance is greater than the focal length, a real, inverted image is formed.

.The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

^ The image vector is at an angle 180° + q to the object vector.

^ On the other hand, as the observer recedes from the object, the apparent size, and also the image on the retina diminishes; details become more and more confused, and gradually, after a while, disappear altogether, and ultimately the external configuration of the object as a whole is no longer recognizable.

.The ratio between the real size of the object y (fig.^ The ratio between the real size of the object y (fig.

^ The magnification is also expressed as the ratio of the apparent size of the object observed through the microscope to the apparent size of the object seen with the naked eye.

^ The difference between the two positions gives the size of the object.

I) FIG. I.
and the distance .1, which is equal to the tangent of the visual angle w, is termed the " apparent size " of the object.^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

^ The greater the visual angle, the more distinctly are the details of the object perceived.

^ As we saw above, the apparent size of a detail of an object must be greater than the angular range of vision, i.e.

.From the figure, which represents vision with a motionless eye, it is seen that the apparent size increases as the object under observation is approached.^ The apparent size of the object seen through the lens is then tan w' = y/f.

^ From the figure, which represents vision with a motionless eye, it is seen that the apparent size increases as the object under observation is approached.

^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

.The greater the visual angle, the more distinctly are the details of the object perceived.^ The greater the visual angle, the more distinctly are the details of the object perceived.

^ As we saw above, the apparent size of a detail of an object must be greater than the angular range of vision, i.e.

^ Therefore we can assume that a detail which appears under an angle of 2' can be surely perceived.

.On the other hand, as the observer recedes from the object, the apparent size, and also the image on the retina diminishes; details become more and more confused, and gradually, after a while, disappear altogether, and ultimately the external configuration of the object as a whole is no longer recognizable.^ On the other hand, as the observer recedes from the object, the apparent size, and also the image on the retina diminishes; details become more and more confused, and gradually, after a while, disappear altogether, and ultimately the external configuration of the object as a whole is no longer recognizable.

^ The new instrument was, however, a big disappointment at first when we realized that at this "small region radiation" the image of the specimen fields, which was now no longer hot, became so dark within seconds that all initially visible details disappeared.
  • ernst.ruska.de 1 February 2010 1:54 UTC ernst.ruska.de [Source type: FILTERED WITH BAYES]

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

.This case arises when the visual angle, under which the object appears, is approximately a minute of arc; it is due to the physiological construction of the retina, for the ends of nerve fibres, which receive the impression of light, have themselves a definite size.^ This case arises when the visual angle, under which the object appears, is approximately a minute of arc; it is due to the physiological construction of the retina, for the ends of nerve fibres , which receive the impression of light, have themselves a definite size.

^ Very often such stereoscopic lenses, owing to faulty construction, give a false idea of space, ignoring the errors which are due to the alteration of the inter-pupillary distance and the visual angles belonging to the principal rays at the object-side (see Binocular Instruments ).

^ In entocentric transmission this phenomenon appears in general as in the case of the contemplation of perspective representations at a too short distance, the objects appearing flattened.

.The lower limit of the resolving power of the eye is reached when the distance is approximately 3438 times the size of the object.^ The lower limit of the resolving power of the eye is reached when the distance is approximately 3438 times the size of the object.

^ However, resolving power remains limited.

^ Finally, this microscopy method remains based on light and therefore is limited by the wavelength used (resolving power ~2000 angstroms, magnification ~2000x).

.If the object be represented by two separate points, these points would appear distinct to the normal eye only so long as the distance between them is at the most only 3438 times smaller than their distance from the eye.^ If the object be represented by two separate points, these points would appear distinct to the normal eye only so long as the distance between them is at the most only 3438 times smaller than their distance from the eye.

^ Moreover, this distance between the object and eye is substantially increased in the compound microscope by the stand; the inconveniences, and in certain circumstances also the dangers, to the eye which may arise, for example by warming the object, are also avoided.

^ A very marked diminution in illumination occurs, however, when the exit pupil of the instrument is smaller than the pupil of the eye.

.When the latter distance is increased still further, the two appear as one.^ When the latter distance is increased still further, the two appear as one.

^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

^ This construction was further improved (I) by introducing a diaphragm between the two lenses; (2) by altering the distance between the two lenses; and (3) by splitting the lower lens into two lenses.

.Therefore when it is desired to distinctly recognize exceedingly small objects or details of such, they are brought as near as possible to the eye.^ Therefore when it is desired to distinctly recognize exceedingly small objects or details of such, they are brought as near as possible to the eye.

^ Eye fatigue can also be a major problem for operators, especially if they have poor vision resulting from near and far sightedness or astigmatism.
  • Nikon MicroscopyU | Concepts and Formulas in Microscopy: Basic Microscope Ergonomics 23 January 2010 9:54 UTC www.microscopyu.com [Source type: FILTERED WITH BAYES]

^ When the shortest distance obtained by the highest strain of accommodation is insufficient to recognize small objects, distinct vision is possible at even a shorter distance by placing a very small diaphragm between the eye and the object, the pencils of rays proceeding from the object-points, which otherwise are limited by the pupils of the eye, being thus restricted by the diaphragm.

.The eye is strained in bringing its focal length to the smallest possible amount, and when this strain is long continued it may cause pain.^ The eye is strained in bringing its focal length to the smallest possible amount, and when this strain is long continued it may cause pain .

^ The focal length of this magnetic electron lens can be changed continuously by means of the coil current.
  • ernst.ruska.de 1 February 2010 1:54 UTC ernst.ruska.de [Source type: FILTERED WITH BAYES]

^ By a correct choice of the focal length of the illuminating lens in relation to the focal length of the mirror, it is possible to choose the size of the image of the source of light so that the whole object-field is uniformly lighted.

.When the shortest distance obtained by the highest strain of accommodation is insufficient to recognize small objects, distinct vision is possible at even a shorter distance by placing a very small diaphragm between the eye and the object, the pencils of rays proceeding from the object-points, which otherwise are limited by the pupils of the eye, being thus restricted by the diaphragm.^ When the shortest distance obtained by the highest strain of accommodation is insufficient to recognize small objects, distinct vision is possible at even a shorter distance by placing a very small diaphragm between the eye and the object, the pencils of rays proceeding from the object-points, which otherwise are limited by the pupils of the eye, being thus restricted by the diaphragm.

^ RESOLUTION LIMIT : smallest separation of points which can be recognized as distinct.

^ The position of the diaphragm limiting the pencils proceeding from the object-points is not constant in the compound microscope.

.The object is then projected with such acute pencils on the plane focused for, in this case on the plane on which the eye can just accommodate itself, that the circle of confusion arising there is still so small that it is below the limit of angular visual distinctness and on that account appears as a sharp point.^ Move the tube of the magnifyer until the objects appear nearly distinct, then with your eye at the sight hole turn gently the stage adjusting rod until the objects appear the most distinct and best defined as possible.
  • Transylvania University Philosophical Museum - PhilosophicalApparatus 23 January 2010 9:54 UTC homepages.transy.edu [Source type: FILTERED WITH BAYES]

^ Eyes - eyepieces should rest just below the eyes with the eyes looking downward at an angle 30 to 45 degrees below the horizontal; interocular distance of binocular eyepieces should be adjusted to ensure that both eyes are focusing comfortably.
  • Nikon MicroscopyU | Concepts and Formulas in Microscopy: Basic Microscope Ergonomics 23 January 2010 9:54 UTC www.microscopyu.com [Source type: FILTERED WITH BAYES]

^ There are small doors at the sides, the front panel can be lifted, and the entire casing can be removed from the balance.
  • Transylvania University Philosophical Museum - PhilosophicalApparatus 23 January 2010 9:54 UTC homepages.transy.edu [Source type: FILTERED WITH BAYES]

.However, the loss of light in this procedure is extraordinarily large, so that only most intensely illuminated objects can be investigated.^ However, the loss of light in this procedure is extraordinarily large, so that only most intensely illuminated objects can be investigated.

^ Since, however, only relatively low powers are now employed, the ordinary rack and pinion movement for focusing suffices, and for the illuminating the object only a mirror below the stage is required when the object is transparent, and a condensing lens above the stage when opaque.

^ The large loss of light, which is caused in dark-field illumination by the cutting off of the direct cone of rays, must be compensated by employing exceptionally strong sources.

.A naked short-sighted eye, which would be corrected for distant objects by a spectacle glass of - Io diopters, may approach the object up to about 4 in.^ A naked short-sighted eye, which would be corrected for distant objects by a spectacle glass of - Io diopters, may approach the object up to about 4 in.

^ In most microscopic observations the object is mounted on a plane glass plate or slide about o 06 in.

^ Especially powerful achromatic condensers are really only magnified microscope objectives, with the difference that they are not corrected for the thickness of the cover slip, but for the thickness of the glass on which the object is placed.

and have a sharp image upon the retina without any strain whatever. .For the observation of small objects, a myopic eye is consequently superior to a normal eye; and the normal eye in its turn is superior to the hypermetropic one.^ For the observation of small objects, a myopic eye is consequently superior to a normal eye; and the normal eye in its turn is superior to the hypermetropic one.

^ In consequence of these residual aberrations, every object-point is not reproduced in an ideal image-point, but as a small circle of aberration.

^ Therefore when it is desired to distinctly recognize exceedingly small objects or details of such, they are brought as near as possible to the eye.

.When the details are no longer recognizable by the unaided eye, the magnifying glass or the simple microscope is necessary.^ A combination microscope, telescope, and magnifying glass.

^ When the details are no longer recognizable by the unaided eye, the magnifying glass or the simple microscope is necessary.

^ On the other hand, as the observer recedes from the object, the apparent size, and also the image on the retina diminishes; details become more and more confused, and gradually, after a while, disappear altogether, and ultimately the external configuration of the object as a whole is no longer recognizable.

.As a rule large magnification is not demanded from the former, but a larger field of view, whilst the simple microscope should ensure powerful magnification even when the field is small.^ The magnification, resulting from the simple microscope of i in.

^ E Field’s simple microscope.
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^ As a rule large magnification is not demanded from the former, but a larger field of view, whilst the simple microscope should ensure powerful magnification even when the field is small.

.The simple microscope enlarges the angle of vision, and does not tire the eye when it is arranged so that the image lies in the farthest limit of distinct vision (the punctum remotum). A normal eye will therefore see an image formed by the magnifying glass most conveniently when it is produced at a great distance, i.e. when the object is in its front focal plane.^ A normal eye will therefore see an image formed by the magnifying glass most conveniently when it is produced at a great distance, i.e.

^ The plane in the object conjugate to the focal plane of the eye-piece is the plane FIG. 14.

^ A combination microscope, telescope, and magnifying glass.

If y (fig. 2) be the object the image appears to a normal FIG. 2.
eye situated behind the system .L with passive accommodation at a very great distance under the angle w'. Since H' P = F 0, = y, from the focal length of the simple microscope, the visual angle w' is given by tan w'/y=I/f'=V, (I) in which f', = H' F', is the image-side focal length (see Lens).^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ In the TEM the magnification (focal length) of the objective remains fixed while the focal length of the projector lens is changed to vary magnification.

^ An intermediate lens must be placed in the body tube to focus this image on the focal plane of the eyepiece.
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.Since the lens is bounded by air, the imageand object-side focal lengths f' and f are equal.^ Since the lens is bounded by air , the imageand object-side focal lengths f' and f are equal.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ In the TEM the magnification (focal length) of the objective remains fixed while the focal length of the projector lens is changed to vary magnification.

.The value Iif' or V in (I), is termed the power of the lens.^ The value Iif' or V in (I), is termed the power of the lens.

.In most cases the number of " diameters " of the simple microscope is required; i.e. the ratio between the apparent sizes of the object when observed through the microscope and when viewed by the naked eye.^ The ratio between the real size of the object y (fig.

^ The apparent size of the object seen through the lens is then tan w' = y/f.

^ The magnification is also expressed as the ratio of the apparent size of the object observed through the microscope to the apparent size of the object seen with the naked eye.

.When a person of normal vision views a small object, he brings it to the distance of distinct vision, which would average about 10 in.^ The angular size of the object at the closest distance for comfortable viewing is 1"/10" or 1/10.

^ When a person of normal vision views a small object, he brings it to the distance of distinct vision, which would average about 10 in.

^ If the object be represented by two separate points, these points would appear distinct to the normal eye only so long as the distance between them is at the most only 3438 times smaller than their distance from the eye.

.The apparent size is then (fig.^ The apparent size is then (fig.

.I) tan w = y/l, where l = i o in., whilst the apparent size of the object viewed through the magnifying glass would result from the formula (I) tan w' = y/f. Consequently the number of diameters will be N = tan w'/tan w = y/f.^ The image viewed through the eyepiece appears then to the observer under the angle w", and as with the single microscope tan w" = I /f 2 ' (4) where f' 2 is the image-side focal length of the eyepiece.

^ Consequently the number of diameters will be N = tan w'/tan w = y/f.

^ Through the large free working distance, which for certain work offers great advantages, the size of the field of view is diminished.

l/y = i/f =
.V.1; (2) it is thus equal to the magnifying power multiplied by the distance of distinct vision, or the number of times that the focal length is contained in Io in.^ Let f = lens focal length, x o = distance of object in front of the lens, and x i = distance of image behind the lens.

^ Put aside the smaller and more powerful lenses that are used to magnify the picture frame numbers.
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^ When the object distance is less than the focal length, a virtual, erect image is formed; its position is obtained by projecting the principal rays backward.

.Since this value for the distance of distinct vision is only conventional, it is understood that the capacity of the simple microscope given in (2) holds good only for eyes accustomed to examine small objects io in.^ Since the amount of variation experienced may be due to the direction and distance that the stage moves, many different movement vectors should be examined.

^ Since the distance that the stage moved is known (subject to the errors of the stage variation) and the distance in pixels is known from the correlation calculation, the two values can be related to determine the size of a pixel.

^ Any magnification above the value given by the above formula represents empty magnification , since such magnification leads to no more useful information but rather a magnified blur.

away; and observation through the magnifying glass must be undertaken by the normal eye with passive accommodation. A lens of i in. focal length must be spoken of, according to this notation, as a X 10 lens, and a lens of in. focal length as a X loo lens. .Obviously the position of a normal eye free from accommodation is immaterial for determining the magnification.^ IT/ that it is to be viewed by a normal 0, p F, eye with passive accommodation.

^ Obviously the position of a normal eye free from accommodation is immaterial for determining the magnification.

^ F2, where a normal eye without accommodation can observe it.

.A X Jo magnification is, however, by no means guaranteed to a myopic eye of - io D by a lens of i in.^ A X Jo magnification is, however, by no means guaranteed to a myopic eye of - io D by a lens of i in.

^ Nothing is altered as to objective magnification, however, as the first surface is plane, and the employment of the immersion means that the value of f l ' 'is unaltered.

focus. .Since this shortsighted observer can view the object with the naked eye with no inconvenience to himself at 4 in.^ Since this shortsighted observer can view the object with the naked eye with no inconvenience to himself at 4 in.

^ The magnification is also expressed as the ratio of the apparent size of the object observed through the microscope to the apparent size of the object seen with the naked eye.

^ Increasing the field of view and the distance from the observer's eyes to the microscope has been the target of a growing number of aftermarket products.
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distance, it follows .(to him) the apparent size is tan w =y14; and to secure convenient vision through the lens the short-sighted person would bring the object to such a distance that a virtual, magnified image would be projected in his punctum remotum. In addition it will be supposed that the centre of the pupil of the observer coincides with the back focal point of the system.^ With this, the objectpoint 0, and consequently the image-point 0' also, will be at a quite definite distance from the centre.

^ Let f = lens focal length, x o = distance of object in front of the lens, and x i = distance of image behind the lens.

^ In each example, the lens is converging , with identical front and back focal points.

.The apparent size of the object seen through the lens is then tan w' = y/f. The magnification, resulting from the simple microscope of i in.^ The apparent size of the object seen through the lens is then tan w' = y/f.

^ The magnification is also expressed as the ratio of the apparent size of the object observed through the microscope to the apparent size of the object seen with the naked eye.

^ The magnification, resulting from the simple microscope of i in.

focus, is here .N = tan w'/tan w = y/f.4/y=4/f=4 Thus, while a lens of i in.^ N = tan w'/tan w = y/f.4/y=4/f=4 Thus, while a lens of i in.

focal length assures to the normal-sighted person a .X 10 magnification, it affords to the short-sighted individual only X 4. On the other hand, it is even of greater use to the hypermetropic than to the observer of normal sight.^ However, even though the fabrication of objectives is more complex than that of eyepieces, we will try to make a better objective than the one we used in the first section.
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^ The images recorded prior to the Figure 6 C inset were recorded at lower magnifications and the total dose was only 10% of that of the Figure 6 C inset.
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^ Inadequate illumination, image deterioration from lens artifacts, improper use of filters, and other errors contribute not only to inferior images, but also increase the strain of imaging specimens.
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.From this it appears that each observer obtains specific advantages from one and the same simple microscope, and also the individual observer can obtain different magnifications by either using different accommodations, or by viewing in passive accommodation.^ You can use this idea to make objectives that have different magnification.
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^ Individual legs on the positioning plates are adjustable to allow tilting of the microscope, and to provide a high degree of precision with respect to instrument height and viewing angle.
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^ In fact, to obtain sharper images one needs to use achromatic lenses.
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Regulation of the Rays.

.In using optical instruments the eye in general is moved just as in free vision; that is to say, the attention is fixed upon the individual parts of the image one after another, the eye being turned in its cavity.^ The manufacturer also claims that Isis reduces the distraction of eye floaters , which move across the field of vision and are accentuated by viewing specimens in bright illumination.
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^ We would like to have a light source that moved with the microscope e.g: one that is part of the microscope body.
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^ Placing an optical system such as the eye behind the lens, will enable the divergent rays to be focused to form a real image.

.In this case the eye is always directed so that the part of the image which is wished to be viewed exactly falls upon the most sensitive portion of the retina, viz.^ In this case the eye is always directed so that the part of the image which is wished to be viewed exactly falls upon the most sensitive portion of the retina, viz.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

^ After the microscope has been so adjusted that the image of the object to be measured falls exactly in the plane of the cross threads, the object is moved by the micrometer until one edge of the object is exactly covered by a thread.

the macula lutea (yellow spot). .Corresponding to the size of the yellow spot only a small fraction of the image appears particularly distinctly.^ Corresponding to the size of the yellow spot only a small fraction of the image appears particularly distinctly.

^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

^ Fortunately, it is possible to improve the image by stopping-down the size of the objective lens so that the light is allowed to pass through only the central portion of the lens.
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.The other portions which are reproduced on the retina on the regions surrounding the yellow spot will also be perceived, but with reduced definition.^ The other portions which are reproduced on the retina on the regions surrounding the yellow spot will also be perceived, but with reduced definition.

.These external and less sensitive parts of the retina, therefore, merely give information as to the general arrangement of the objects and to a certain extent act as guide-post in order to show quickly and conveniently, although not distinctly, the places in the image which should claim special attention.^ These external and less sensitive parts of the retina, therefore, merely give information as to the general arrangement of the objects and to a certain extent act as guide-post in order to show quickly and conveniently, although not distinctly, the places in the image which should claim special attention.

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

.Vision with a motionless eye, or " indirect vision," gives a general view over the whole object with particular definition of a small central portion.^ Vision with a motionless eye, or " indirect vision," gives a general view over the whole object with particular definition of a small central portion.

^ We still have a large collection of objects made to be viewed with the aid of this particular apparatus.
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^ Therefore when it is desired to distinctly recognize exceedingly small objects or details of such, they are brought as near as possible to the eye.

.Vision with a movable eye, or " direct vision," gives exact information as to the parts of the object one after another.^ Vision with a movable eye, or " direct vision," gives exact information as to the parts of the object one after another.

^ In addition, the particles can only be recognized as separate objects if their apparent distance from one another is greater than the angular definition of sight.

^ By means of screws the stage plate is movable in two directions at right angles to one another, in the plane of the stand.

.The simple microscope permits such vision.^ The simple microscope permits such vision.

^ This permits researches which are impossible with the simple microscope.

^ Where very short focus simple microscopes are employed, using high magnifications, it is imperative to employ a stand which permits exact focusing and the use of a special illuminating apparatus.

.If the instrument has a sensible lens diameter, and is arranged so that the centre of rotation of the eye can coincide with the intersection of the principal rays, the lens can then form with the eye a centred system.^ Placing an optical system such as the eye behind the lens, will enable the divergent rays to be focused to form a real image.

^ Spherical refracting surfaces act as lenses for paraxial rays which are those rays that pass close to the principal axis of the lens.

^ I.22 Focusing effect of lens on rays originating from points on principal axis located at different distances from the lens.

.Such lenses are termed " lenses for direct vision."^ Such lenses are termed " lenses for direct vision."

^ Gullstrand showed how to correct these lenses for direct vision, i.e.

.By moving the eye about its centre of rotation M the whole field can be examined.^ By moving the eye about its centre of rotation M the whole field can be examined.

^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

.The margin of the mount of the lens serves as the diaphragm of the field of view.^ DD =diaphragm of the field of view.

^ D D = diaphragm of field of view.

^ The margin of the mount of the lens serves as the diaphragm of the field of view.

.The selection of the rays emerging from the lens and actually employed in forming the image is undertaken by the pupil of the eye which, in this case, is consequently the exit pupil of the instrument.^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ I0 is the image formed by the objective lens O, I1 is formed by the first projector lens P1 and I2 by the second projector P2, on the screen.

^ Placing an optical system such as the eye behind the lens, will enable the divergent rays to be focused to form a real image.

In fig. 3 P'P' 1 designates the exit pupil of the L FIG. 3.
lens, and the image of .P'P',, i.e. PP 1, which is formed by the lens, limits the aperture of the pencils of rays on the object-side; consequently it is the entrance pupil of the instrument.^ PP 1, which is formed by the lens, limits the aperture of the pencils of rays on the object-side; consequently it is the entrance pupil of the instrument.

^ PP/ is the entrance pupil.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

.Since the exit pupil moves in observing the whole field, the entrance pupil also moves.^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ It is possible to see the whole field through this pupil by slightly moving the head and eye.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

.The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.^ M is therefore the intersection of the principal rays.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

.M is therefore the intersection of the principal rays.^ M is therefore the intersection of the principal rays.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

^ In the case of the negative eyepiece, on the other hand, the divergence of the principal rays through the eyepiece is also further augmented, but their point of intersection is not accessible to the eye.

.So long as the exit pupil is completely filled the brightness of the image will be approximately equal to that of free vision.^ So long as the exit pupil is completely filled the brightness of the image will be approximately equal to that of free vision.

^ P "P1' =virtual image of P1P1' =exit pupil of complete microscope.

^ Eyepoints should be high enough that the field of vision is completely filled, but far enough away so as to avoid contact of eyepieces with the eyelashes.
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.If, however, we fix the points lying towards the margin of the field of view, the diaphragm gradually cuts off more and more of the rays which were necessary to fill the pupil, and in consequence the brightness gradually falls off to zero.^ Viewing field: More than 20mm .
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^ If, however, we fix the points lying towards the margin of the field of view, the diaphragm gradually cuts off more and more of the rays which were necessary to fill the pupil, and in consequence the brightness gradually falls off to zero .

^ DD =diaphragm of the field of view.

.This vignetting can be observed in all lenses.^ This vignetting can be observed in all lenses.

.In most cases, and also in corrected systems, the intersection of the principal rays is no longer available for the centre of rotation of the eye, and this kind of observation is impossible.^ M is therefore the intersection of the principal rays.

^ In most cases, and also in corrected systems, the intersection of the principal rays is no longer available for the centre of rotation of the eye, and this kind of observation is impossible.

^ In most cases a diaphragm regulates the rays.

.In some instruments observation of the whole available field is only possible when the head and eye are moved at the same time, the lens retaining its position.^ It is possible to see the whole field through this pupil by slightly moving the head and eye.

^ The lens is brought as close as possible to the eye so as to view as large a field as possible.

^ By moving the eye about its centre of rotation M the whole field can be examined.

Dr M. von Rohr terms this kind of vision " peep-hole observation." .It has mainly to be considered in connexion with powerful magnifying glasses.^ It has mainly to be considered in connexion with powerful magnifying glasses.

^ Especially powerful achromatic condensers are really only magnified microscope objectives, with the difference that they are not corrected for the thickness of the cover slip, but for the thickness of the glass on which the object is placed.

^ In magnifying glasses for direct vision the eye must always be considered.

.In most cases a diaphragm regulates the rays.^ In most cases a diaphragm regulates the rays.

^ In most cases, and also in corrected systems, the intersection of the principal rays is no longer available for the centre of rotation of the eye, and this kind of observation is impossible.

Fig. 4 shows the position of the diaphragms, to be considered in this kind of observation. .PP1 is the"entrance pupil, P'P1' the exit pupil, and GG the diaphragm.^ PP1 is the"entrance pupil, P'P1' the exit pupil, and GG the diaphragm.

^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ This image P"P i " is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system.

.The intersection of the principal rays in this case lies in the middle of the entrance pupil or of the exit pupil.^ M is therefore the intersection of the principal rays.

^ The intersection of the principal rays in this case lies in the middle of the entrance pupil or of the exit pupil.

^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

.By head and eye motion FIG 4. the various parts of the whole field can be viewed one after another.^ The manufacturer also claims that Isis reduces the distraction of eye floaters , which move across the field of vision and are accentuated by viewing specimens in bright illumination.
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^ Another problem with this lens is that it has quite a narrow field of view.
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^ Unfortunately, this separation introduces several problems, one of which is that the eye lens will focus on any imperfections and dust particles on the field lens.
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.The distance of the eye from the lens is here immaterial.^ The distance of the eye from the lens is here immaterial.

^ The distance between the lenses must be equal to half of the sum of the respective focal lengths: d = (fa+fb)/2, where fa is the field lens focal length and fb is the eye lens focal length.
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.In this case also the illumination must fall to zero by the vignetting of the pencils coming from objects at the margin of the field of view.^ In this case also the illumination must fall to zero by the vignetting of the pencils coming from objects at the margin of the field of view.

^ The manufacturer also claims that Isis reduces the distraction of eye floaters , which move across the field of vision and are accentuated by viewing specimens in bright illumination.
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^ To fully utilize the aperture of the system all dispersing rays in the object-space of the objective must be retained in the imagespace of the illuminating system.

.C and D are the outermost rays which can pass through the instrument.^ C and D are the outermost rays which can pass through the instrument.

^ All rays issuing from this point pass unrefracted through the dividing surface; its image-point coincides with it.

^ All rays passing through the geometrical center of the lens are undeviated and pass straight on, no matter from which direction they come.

.Magnifying glasses are often used for viewing three-dimensional objects.^ Magnifying glasses are often used for viewing three-dimensional objects.

^ Johnson, E M, and J J Capowski, "Principles of reconstruction and three-dimensional display of serial sections using a computer," The microcomputer in cell and neurobiology research (1985).

^ These early three-dimensional reconstructions typically were of gross anatomy and certain anatomical landmarks were used to align the drawings of each section.

.Only points lying on the plane focused for can be sharply reproduced in the retina, which acts as object-plane to the retina.^ Only points lying on the plane focused for can be sharply reproduced in the retina, which acts as object-plane to the retina.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

^ Object points lying out tive eyepiece.

' See also Lens.
.XVIII. 13a F F All points lying out of this plane are reproduced as circles of confusion.^ XVIII. 13a F F All points lying out of this plane are reproduced as circles of confusion.

^ Object points lying out tive eyepiece.

^ In consequence of these residual aberrations, every object-point is not reproduced in an ideal image-point, but as a small circle of aberration.

.The central projection, of which the centre is the middle point of the entrance pupil on the plane focused for, will show in weaker systems, or those very much stopped down, a certain finite depth of definition; that is to say, the totality of points, which lie out of the plane focused for, and which are projected with circles of confusion so small that they appear to the eye as sharp points, will include the sharp object relief, and determine the depth of definition of the lens.^ The central projection , of which the centre is the middle point of the entrance pupil on the plane focused for, will show in weaker systems, or those very much stopped down, a certain finite depth of definition; that is to say, the totality of points, which lie out of the plane focused for, and which are projected with circles of confusion so small that they appear to the eye as sharp points, will include the sharp object relief, and determine the depth of definition of the lens.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

^ XVIII. 13a F F All points lying out of this plane are reproduced as circles of confusion.

.With increasing magnification the depth of definition diminishes, because the circles of confusion are greater in consequence of the shorter focall length.^ With increasing magnification the depth of definition diminishes, because the circles of confusion are greater in consequence of the shorter focall length.

^ In immersion systems the object-side focal length is greater than the imageside focal length.

^ The magnification of a microscope is determined from the focal lengths of the two optical systems and the optical tube length, for N = 250 A/fi'f2 To determine the optical tube length 0, it is necessary to know the position of the focal planes of the objective and of the ocular.

.Very powerful simple microscopes have hardly any depth of definition so that in fact only points lying in one plane can be seen sharply with one focusing.^ Hence, one can focus at a particular plane in the tissue and recover depth information.

^ Simple microscope, English botanical, (very rare).
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^ A simple microscope , on the other hand, comprises a single lens, which is essentially a more or less powerful magnifier.
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Illumination

.So long as the pupil of the observer alone undertakes the regulation of the rays there is no perceptible diminution of illumination in comparison with the naked eye vision.^ So long as the pupil of the observer alone undertakes the regulation of the rays there is no perceptible diminution of illumination in comparison with the naked eye vision.

^ A very marked diminution in illumination occurs, however, when the exit pupil of the instrument is smaller than the pupil of the eye.

^ The manufacturer also claims that Isis reduces the distraction of eye floaters , which move across the field of vision and are accentuated by viewing specimens in bright illumination.
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.The losses of light which occur in this case are due to reflection, which takes place in the passage of the light through the glass surfaces.^ The losses of light which occur in this case are due to reflection, which takes place in the passage of the light through the glass surfaces.

^ In immersion-systems of such considerable aperture no medium of smaller refractive index than the immersion liquid may be placed between the surface of the front lens and the object, as otherwise total reflection would occur.

^ In addition to a considerable increase in brightness the losses due to reflection are avoided; losses which arise in passing to the back surface of the cover-slip and to the front surface of the front lens.

.In a lens with two bounding surfaces in air there is a loss of about 9%; and in a lens system consisting of two separated lenses, i.e. with four surfaces in air, about 17%.^ In a lens with two bounding surfaces in air there is a loss of about 9%; and in a lens system consisting of two separated lenses, i.e.

^ Amici chiefly employed cemented pairs of lenses consisting of a plano-convex flint lens and a biconvex crown lens(fig.

^ This construction was further improved (I) by introducing a diaphragm between the two lenses; (2) by altering the distance between the two lenses; and (3) by splitting the lower lens into two lenses.

Losses due to absorption are almost zero when the lenses are very thin, as with lenses of small diameter. .A very marked diminution in illumination occurs, however, when the exit pupil of the instrument is smaller than the pupil of the eye.^ A very marked diminution in illumination occurs, however, when the exit pupil of the instrument is smaller than the pupil of the eye.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

^ Here also the exit-pupil is accessible to the eye and through it the whole field can be seen by moving the head and eye.

.In such instruments an arrangement is often required to intensely illuminate the object.^ In such instruments an arrangement is often required to intensely illuminate the object.

^ By dark-field illumination it is even possible to make such small details of objects perceptible as are below the limits of the resolving power.

^ It is best if the image of the light is not larger than the object examined, and to effect this, an illuminating lens with an iris diaphragm is often placed between the source of light and the illuminator.

Forms of the Simple Microscope

.If the ordinary convex lens be employed as magnifying glass, great aberrations occur even in medium magnifications.^ If the ordinary convex lens be employed as magnifying glass, great aberrations occur even in medium magnifications.

^ A convex lens of rockcrystal was found by Layard among the ruins of the palace of Nimrud; Seneca describes hollow spheres of glass filled with water as being commonly used as magnifiers.

^ A normal eye will therefore see an image formed by the magnifying glass most conveniently when it is produced at a great distance, i.e.

.These are: (I) chromatic aberration, (2) spherical aberration and (3) astigmatism (see Aberration).^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

^ The serious consequence of this is that neither spherical or chromatic aberrations can be corrected as is done in light optics by the use doublets of positive and negative lenses.

^ This method makes it specially possible to overcome the chromatic and spherical aberrations of higher orders and to fulfil - the sine-condition, and the chief merit of this improvement belongs to Amici.

.When the pupil regulates the aperture of the rays producing the image the aberrations of the ordinary lenses increase considerably with the magnification, or, what amounts to the same thing, with the increase in the curvature of the surfaces.^ When the pupil regulates the aperture of the rays producing the image the aberrations of the ordinary lenses increase considerably with the magnification, or, what amounts to the same thing, with the increase in the curvature of the surfaces.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

^ But, owing to the various partial reflections which the illuminating cone of rays undergoes when traversing the surfaces of the lenses, a portion of the light comes again into the preparation, and into the eye of the observer, thus veiling the image.

.For lenses of short focus the diameter of the pupil is too large, and diaphragms must be employed which strongly diminish the aperture of the pencils, and so reduce the errors, but with a falling off of illumination.^ For lenses of short focus the diameter of the pupil is too large, and diaphragms must be employed which strongly diminish the aperture of the pencils, and so reduce the errors, but with a falling off of illumination.

^ In this case also the illumination must fall to zero by the vignetting of the pencils coming from objects at the margin of the field of view.

^ If, however, we fix the points lying towards the margin of the field of view, the diaphragm gradually cuts off more and more of the rays which were necessary to fill the pupil, and in consequence the brightness gradually falls off to zero .

.To reduce the aberrations Sir David Brewster proposed to employ in the place of glass transparent minerals of high refractive index and low dispersion.^ Schott succeeded, however, in producing glasses which with a comparatively low refraction have a high dispersion, and with a high refraction a low dispersion.

^ To reduce the aberrations Sir David Brewster proposed to employ in the place of glass transparent minerals of high refractive index and low dispersion .

^ A microscope, using concave mirrors, was proposed in 1672 by Sir Isaac Newton ; and he was succeeded by Barker, R. Smith, B. Martin , D. Brewster, and, above all, Amici.

.In this manner lenses of short focus can be produced having lower curvatures than glass lenses necessitate.^ In this manner lenses of short focus can be produced having lower curvatures than glass lenses necessitate.

^ Antony van Leeuwenhoek appears to be the first to succeed in grinding and polishing lenses of such short focus and perfect figure as to render the simple microscope a better instrument for most purposes than any compound microscope then constructed.

^ The single refracting surface of spherical curvature is the fundamental unit of focusing action by glass lenses .

.The diamond has the requisite optical properties, its index of refraction being about i 6 times as large as that of ordinary glass.^ The diamond has the requisite optical properties, its index of refraction being about i 6 times as large as that of ordinary glass.

^ The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index.

^ Advantages/Disadvantages of electron lenses: The fact that the refractive index does not change abruptly in electron lenses has one advantage in that there are no troublesome reflections at equipotentials as at glass interfaces.

.The spherical aberration of a diamond lens can be brought down to one-ninth of a glass lens of equal focus.^ The spherical aberration of a diamond lens can be brought down to one-ninth of a glass lens of equal focus.

^ Correction of the spherical aberration in strong systems with very large aperture can not be brought about by means of a single combination of two lenses, but several partial systems are necessary.

^ One of the main problem with any lens is chromatic aberration which has to do with the inability of a lens to focus light of differing wavelengths to the same point.
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.Apart, however, from the cost of the mineral and its very difficult working, a source of error lies in its want of homogeneity, which often causes a doublh or even a triple image.^ Apart, however, from the cost of the mineral and its very difficult working, a source of error lies in its want of homogeneity, which often causes a doublh or even a triple image.

^ In addition, application of this threshold was very dependent on the imaging characteristics of the image set used and made reproducibility, hence reliable automated contour extraction, difficult.

^ Even in powerful magnifications a good image exists in all parts of a relatively large field, and the free working distance is fairly large.

.Similar attempts made by Pritchard with sapphires were more successful.^ Similar attempts made by Pritchard with sapphires were more successful.

^ This method (morphological custer) was more successful than previous attempts at edge detection.

.With this mineral also spherical and chromatic aberration are a fraction of that of a glass lens, but double refraction, which involves a doubling of the image, is fatal to its use.^ With this mineral also spherical and chromatic aberration are a fraction of that of a glass lens, but double refraction, which involves a doubling of the image, is fatal to its use.

^ Spherical refracting surfaces act as lenses for paraxial rays which are those rays that pass close to the principal axis of the lens.

^ The serious consequence of this is that neither spherical or chromatic aberrations can be corrected as is done in light optics by the use doublets of positive and negative lenses.

.Improvements in glass lenses, however, have rendered further experiments with precious stones unnecessary.^ Improvements in glass lenses, however, have rendered further experiments with precious stones unnecessary.

^ Further, the different transparencies of the cells for the ultra-violet rays render it unnecessary to dye the preparations.

^ Any further improvement will require the use of achromatic lenses.
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The simplest was a sphere of glass, the equator of which (i.e. the mount) formed the diaphragm. Wollaston altered this by taking two piano-convex lenses, placing the plane surfaces towards each other and employing a diaphragm between the two parts (fig 5).
Wollaston. Brewster. Brewster (Stanhope).
FIG. 5. FIG. 6. FIG. 7.
.Sir David Brewster found that Wollaston's form worked best when the two lenses were hemispheres and the central space was filled up with a transparent cement having the same refractive index as the glass; he therefore used a sphere and provided it with a groove at the equator (see fig.^ In the absence of electrostatic fields, the refractive index is the same in object and image space , therefore f 1  =  f 2 .

^ Sir David Brewster found that Wollaston's form worked best when the two lenses were hemispheres and the central space was filled up with a transparent cement having the same refractive index as the glass; he therefore used a sphere and provided it with a groove at the equator (see fig.

^ A microscope, using concave mirrors, was proposed in 1672 by Sir Isaac Newton ; and he was succeeded by Barker, R. Smith, B. Martin , D. Brewster, and, above all, Amici.

6). .Coddington employed the same construction, and for this reason this device is frequently called the Coddington lens; although he brought the Wollaston-Brewster lens into general notice, he was neither the inventor nor claimed to be.^ Coddington employed the same construction, and for this reason this device is frequently called the Coddington lens; although he brought the Wollaston-Brewster lens into general notice, he was neither the inventor nor claimed to be.

^ This construction was further improved (I) by introducing a diaphragm between the two lenses; (2) by altering the distance between the two lenses; and (3) by splitting the lower lens into two lenses.

^ A construction also employing one piece of glass forms the so-called Stanhope lens (fig.

.This lens reproduced all points of a concentric spherical surface simultaneously sharp.^ This lens reproduced all points of a concentric spherical surface simultaneously sharp.

^ Spherical refracting surfaces act as lenses for paraxial rays which are those rays that pass close to the principal axis of the lens.

^ Interference/diffraction/coherence An ideal lens system obtains an exact image of the object (each point faithfully reproduced).

.A construction also employing one piece of glass forms the so-called Stanhope lens (fig.^ A construction also employing one piece of glass forms the so-called Stanhope lens (fig.

^ The watchmaker's glass is one of the earliest forms of this kind.

^ Amici chiefly employed cemented pairs of lenses consisting of a plano-convex flint lens and a biconvex crown lens(fig.

7), which was really due to Brewster. .This is a glass cylinder, the two ends of which are spherical surfaces.^ This is a glass cylinder , the two ends of which are spherical surfaces.

^ The single refracting surface of spherical curvature is the fundamental unit of focusing action by glass lenses .

.The more strongly curved surface is placed next the eye, the other serves at the same time as specimen carrier.^ The more strongly curved surface is placed next the eye, the other serves at the same time as specimen carrier .

^ A fixed mark which serves as an index is placed on the lower side of the collective lens and is seen clearly at the same time as the graduation of the movable slide.

^ Normally, the lenses are placed with the plane or concave surface toward the specimen.
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.This lens is employed in articles found in tourist resorts as a magnifying glass for miniature photographs of the locality.^ This lens is employed in articles found in tourist resorts as a magnifying glass for miniature photographs of the locality.

^ A convex lens of rockcrystal was found by Layard among the ruins of the palace of Nimrud; Seneca describes hollow spheres of glass filled with water as being commonly used as magnifiers.

^ If the ordinary convex lens be employed as magnifying glass, great aberrations occur even in medium magnifications.

Doublets, &'c. - .To remove the errors which the above lenses showed, particularly when very short focal lengths were in question, lens combinations were adopted.^ To remove the errors which the above lenses showed, particularly when very short focal lengths were in question, lens combinations were adopted.

^ As these lenses all have the same focal length, the eyepiece has to follow the Ramsden scheme, which is explained later on.
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^ This lens should have a focal length of about 25 mm, and it must have the plane surface turned upward.
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.The individual components required weaker curvatures and permitted of being more correctly manufactured, and, more particularly, the advantage of reduced aberrations was the predominant factor.^ The individual components required weaker curvatures and permitted of being more correctly manufactured, and, more particularly, the advantage of reduced aberrations was the predominant factor.

.Wollaston's doublet (fig.^ Wollaston's doublet (fig.

.8) is a combination of two piano-convex lenses, the focal lengths of which are in the ratio of 3: I; the plane Wollaston.^ The focal plane of the Huygens eyepiece is located between the two lenses.
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^ In general, the two focal lengths have to be in the ratio somewhere between 1:3 and 1:2.
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^ This is just the average of the two focal lengths.
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Fraunhofer. Wilson. Steinheil. Chevalier (Briicke).
FIG. 8. FIG 9. FIG. IO. FIG. II. FIG. 12.
sides are turned towards the object, and the smaller of the two lenses is nearer the object. .This construction was further improved (I) by introducing a diaphragm between the two lenses; (2) by altering the distance between the two lenses; and (3) by splitting the lower lens into two lenses.^ The shortest distance between 2 disks at which the two disks appear partially separated corresponds to about 1/2 the width of the disks.

^ The rationale is that, if we can minimize the distance between the centers of all the contours on a section with those of the adjacent section, then we will converge on the optimal fit for the two sections.

^ The focal plane of the Huygens eyepiece is located between the two lenses.
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.Triplets are employed when the focal length of the simple microscope was less than in.^ Triplets are employed when the focal length of the simple microscope was less than in.

^ Strong systems produce in the proximity of their back focal plane an image of the scale, which can be inspected with a weak auxiliary microscope, and the length of the visible part of the graduation determined.

^ In immersion systems the object-side focal length is greater than the imageside focal length.

.When well made such constructions are almost free from spherical aberration, and the chromatic errors are very small.^ This is a very nice and well made microscope.
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^ Figure 87 represents a small (9 5/8 x 5 x 4 inches) well made box which is divided into eight compartments.
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^ The serious consequence of this is that neither spherical or chromatic aberrations can be corrected as is done in light optics by the use doublets of positive and negative lenses.

.Similar doublets composed of two piano-convex lenses are the Fraunhofer (fig.^ You can make a high quality eyepiece with only two plano-convex lenses.
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^ Try to use a plano-convex lens followed by an achromatic doublet, or two equal doublets.
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^ The Ramsden eyepiece is made with two plano-convex lenses of same focal length (fa = fb), with the convex surfaces facing each other (Figure 10).
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9) and the Wilson (fig. io). .Axial aberration is reduced by distributing the refraction between two lenses; and by placing the two lenses farther apart the errors of the pencils of rays proceeding from points lying outside the axis are reduced.^ Axial aberration is reduced by distributing the refraction between two lenses; and by placing the two lenses farther apart the errors of the pencils of rays proceeding from points lying outside the axis are reduced.

^ When the shortest distance obtained by the highest strain of accommodation is insufficient to recognize small objects, distinct vision is possible at even a shorter distance by placing a very small diaphragm between the eye and the object, the pencils of rays proceeding from the object-points, which otherwise are limited by the pupils of the eye, being thus restricted by the diaphragm.

^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

.The Wilson has a greater distance between the lenses, and also a reduction of the chromatic difference of magnification, but compared with the Fraunhofer it is at a disadvantage with regard to the size of the free working distance, i.e. the distance of the object from the lens surface nearer it.^ The Wilson has a greater distance between the lenses, and also a reduction of the chromatic difference of magnification, but compared with the Fraunhofer it is at a disadvantage with regard to the size of the free working distance, i.e.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

.By introducing a dispersive lens of flint the magnifying glass could be corrected for both chromatic and spherical aberrations.^ The aberrations, both spherical and chromatic, increase very rapidly with the aperture.

^ By introducing a dispersive lens of flint the magnifying glass could be corrected for both chromatic and spherical aberrations.

^ The lens is spherically corrected for 00', but the sinecondition is not fulfilled.

.Browning's " platyscopic " lens and the Steinheil " aplanatic " lens (fig.^ Browning's " platyscopic " lens and the Steinheil " aplanatic " lens (fig.

II) are of this type. .Both yield a field of good definition free from colour.^ Both yield a field of good definition free from colour.

^ Even in powerful magnifications a good image exists in all parts of a relatively large field, and the free working distance is fairly large.

.The manner in which the eye uses such a lens was first effectively taken into account by M. von Rohr.^ The manner in which the eye uses such a lens was first effectively taken into account by M. von Rohr.

^ Placing an optical system such as the eye behind the lens, will enable the divergent rays to be focused to form a real image.

^ Similarly, you can modify the Huygens eyepiece with an achromatic eye lens, and, in this case you could use a biconvex lens for the field lens.
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.These anastigmatic lenses, which are manufactured up to X 40, are chromatically and spherically corrected, and for a middle diaphragm the errors of lateral pencils, distortion, astigmatism and coma are eliminated.^ These anastigmatic lenses, which are manufactured up to X 40, are chromatically and spherically corrected, and for a middle diaphragm the errors of lateral pencils, distortion, astigmatism and coma are eliminated.

^ Unlike the eyepiece, which can be at least partially corrected for chromatic aberration without using achromatic lenses, the objectives can not.
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^ As these lenses all have the same focal length, the eyepiece has to follow the Ramsden scheme, which is explained later on.
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." Peephole " observation is employed, observation being made by moving the head and eye while the lens is held steady.^ Peephole " observation is employed, observation being made by moving the head and eye while the lens is held steady.

^ It is possible to see the whole field through this pupil by slightly moving the head and eye.

^ Here also the exit-pupil is accessible to the eye and through it the whole field can be seen by moving the head and eye.

.Even in powerful magnifications a good image exists in all parts of a relatively large field, and the free working distance is fairly large.^ Even in powerful magnifications a good image exists in all parts of a relatively large field, and the free working distance is fairly large.

^ Both yield a field of good definition free from colour.

^ To examine objects with objectives of high power and low free object distance, the apparatus for side-illumination is not sufficient, and a so-called vertical illuminator is used.

.For especially large free working distances the corrections proposed by Chevalier and carried out by E. Briicke must be noticed (fig.^ For especially large free working distances the corrections proposed by Chevalier and carried out by E. Briicke must be noticed (fig.

^ Through the large free working distance, which for certain work offers great advantages, the size of the field of view is diminished.

^ Even in powerful magnifications a good image exists in all parts of a relatively large field, and the free working distance is fairly large.

12). .To an achromatic collective lens, which is turned towards the object, a dispersive lens is combined (this type to a certain extent belongs to the compound microscope).^ To an achromatic collective lens, which is turned towards the object, a dispersive lens is combined (this type to a certain extent belongs to the compound microscope).

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ Dollond’s achromat required a combination of concave flintglass (strong dispersion) with a convex crown glass (weak dispersion).
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.By altering the distance of the collective and dispersive members the magnification can be widely varied.^ By altering the distance of the collective and dispersive members the magnification can be widely varied.

^ The factors are electromagnet hysteresis (producing an altered magnification), focus variation (inducing an image enlargement and rotation), and variation in stage control (producing an imprecise movement).

.Through the large free working distance, which for certain work offers great advantages, the size of the field of view is diminished.^ Through the large free working distance, which for certain work offers great advantages, the size of the field of view is diminished.

^ Even in powerful magnifications a good image exists in all parts of a relatively large field, and the free working distance is fairly large.

^ The Wilson has a greater distance between the lenses, and also a reduction of the chromatic difference of magnification, but compared with the Fraunhofer it is at a disadvantage with regard to the size of the free working distance, i.e.

.In magnifying glasses for direct vision the eye must always be considered.^ In magnifying glasses for direct vision the eye must always be considered.

^ A normal eye will therefore see an image formed by the magnifying glass most conveniently when it is produced at a great distance, i.e.

^ In this case the eye is always directed so that the part of the image which is wished to be viewed exactly falls upon the most sensitive portion of the retina, viz.

.The lens is brought as close as possible to the eye so as to view as large a field as possible.^ The lens is brought as close as possible to the eye so as to view as large a field as possible.

^ Another problem with this lens is that it has quite a narrow field of view.
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^ It is possible to see the whole field through this pupil by slightly moving the head and eye.

.The watchmaker's glass is one of the earliest forms of this kind.^ The watchmaker's glass is one of the earliest forms of this kind.

^ A construction also employing one piece of glass forms the so-called Stanhope lens (fig.

.Gullstrand showed how to correct these lenses for direct vision, i.e. to eliminate distortion and astigmatism when the centre of rotation of the eye coincided with the point where the principal rays crossed the axis.^ Such lenses are termed " lenses for direct vision."

^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

^ Gullstrand showed how to correct these lenses for direct vision, i.e.

.Von Rohr fulfilled this condition by constructing the Verant lens, which are low power systems intended for viewing a large flat field.^ Von Rohr fulfilled this condition by constructing the Verant lens, which are low power systems intended for viewing a large flat field.

^ The lens is brought as close as possible to the eye so as to view as large a field as possible.

^ Since in these systems the sine-condition can be fulfilled for several colours, the quality of the images of points beyond the axis is better.

Stands

.For dissecting or examining objects it is an advantage to have both hands free.^ For dissecting or examining objects it is an advantage to have both hands free.

^ To examine objects with objectives of high power and low free object distance, the apparatus for side-illumination is not sufficient, and a so-called vertical illuminator is used.

.Where very short focus simple microscopes are employed, using high magnifications, it is imperative to employ a stand which permits exact focusing and the use of a special illuminating apparatus.^ Where very short focus simple microscopes are employed, using high magnifications, it is imperative to employ a stand which permits exact focusing and the use of a special illuminating apparatus.

^ The magnification, resulting from the simple microscope of i in.

^ This permits researches which are impossible with the simple microscope.

.Since, however, only relatively low powers are now employed, the ordinary rack and pinion movement for focusing suffices, and for the illuminating the object only a mirror below the stage is required when the object is transparent, and a condensing lens above the stage when opaque.^ Since, however, only relatively low powers are now employed, the ordinary rack and pinion movement for focusing suffices, and for the illuminating the object only a mirror below the stage is required when the object is transparent, and a condensing lens above the stage when opaque.

^ This includes points above the stage for the illumination of opaque objects.
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^ Illumination of transparent objects is effected by the universal-jointed mirror.

.Dissecting stands vary as to portability, the size of the stand, and the manner in which the arm-rests are arranged.^ Dissecting stands vary as to portability, the size of the stand, and the manner in which the arm-rests are arranged.

.A stand is shown in fig.^ A stand is shown in fig.

57 (Plate). On the heavy horseshoe foot is a column carrying the stage. In the column is the guide. for the rack-andpinion movement. .Lenses of various magnifications can be adapted to the carrier and moved about over the stage.^ Lenses of various magnifications can be adapted to the carrier and moved about over the stage.

^ Since we can capture an image and programmatically move the stage of the microscope, we can determine the variation in the stage control by testing its repeatability.

^ Since the amount of variation experienced may be due to the direction and distance that the stage moves, many different movement vectors should be examined.

.The rests can be attached to the stage, and when done with folded together.^ The rests can be attached to the stage, and when done with folded together.

.Illumination of transparent objects is effected by the universal-jointed mirror.^ Illumination of transparent objects is effected by the universal-jointed mirror.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ Since, however, only relatively low powers are now employed, the ordinary rack and pinion movement for focusing suffices, and for the illuminating the object only a mirror below the stage is required when the object is transparent, and a condensing lens above the stage when opaque.

.Byj turning the knob A, placed at the front corner of the stage, a black or white plate, forming a dark or light background, can be swung underneath the specimen.^ Byj turning the knob A, placed at the front corner of the stage, a black or white plate, forming a dark or light background, can be swung underneath the specimen.

^ Virtual Image : one from which light rays appear to diverge; rays are not in fact concentrated at the position of a virtual image, so that a photographic plate placed at the position of the image is not exposed (by focused rays).

^ These fringes are formed outside the edge of a hole (white) in a carbon film (black).

.When the recognition of the arrangement in space of small objects is desired a stereoscopic lens can be used.^ When the recognition of the arrangement in space of small objects is desired a stereoscopic lens can be used.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ The arrangement of two lenses so that small objects can be seen magnified followed soon after the discovery of the telescope.

.In most cases refracting and reflecting systems are arranged so that the natural interpupillary distance is reduced.^ In most cases refracting and reflecting systems are arranged so that the natural interpupillary distance is reduced.

^ In most cases, and also in corrected systems, the intersection of the principal rays is no longer available for the centre of rotation of the eye, and this kind of observation is impossible.

^ The cones must be so directed through the divided system that the two exit pupils correspond to the interpupillary distance of the observer.

.Stereoscopic lenses can never be powerful systems, for the main idea is the recognition of the depth of objects, so that only systems having a sufficient depth of definition can be utilized.^ The following expressions will help you to calculate the focal length and the power of simple eyepieces and objectives, assuming they are systems of thin lenses.
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.Very often such stereoscopic lenses, owing to faulty construction, give a false idea of space, ignoring the errors which are due to the alteration of the inter-pupillary distance and the visual angles belonging to the principal rays at the object-side (see Binocular Instruments).^ These small Withering type instruments are very desirable and often sell for surprising sums of money.
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^ Spherical refracting surfaces act as lenses for paraxial rays which are those rays that pass close to the principal axis of the lens.

^ This depends on the angle of the cone of rays it is able to accept from the object.

.Compound Microscope The view held by early opticians, that a compound microscope could never produce such good images as an instrument of the simple type, has proved erroneous; and the principal attention of modern opticians has been directed to the compound instrument.^ The overall type is included which indicates whether it’s a compound or simple microscope.
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^ A Simple hand-held microscope with objects placed on a rotating disk.

^ In this article I describe the construction of a very simple low-cost compound microscope that will give you a magnification of about 75.
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.Although we now know how the errors of lenses may be corrected, and how the simple microscope may be improved, this instrument remains with relatively feeble magnification, and to obtain stronger magnifications the compound form is necessary.^ In this article I describe the construction of a very simple low-cost compound microscope that will give you a magnification of about 75.
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^ With normal lenses (non achromatic) you can obtain fairly good images as long as you limit yourself to moderate magnifications.
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^ To obtain high magnifications, you absolutely require achromatic lenses.
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.By compounding two lenses or lens systems separated by a definite interval, a system is obtained having a focal length considerably less than the focal lengths of the separate systems.^ This is just the average of the two focal lengths.
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^ As these lenses all have the same focal length, the eyepiece has to follow the Ramsden scheme, which is explained later on.
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^ To determine the focal length of these lenses read our article: " From Lenses to Optical Instruments ".
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.If f and f' be the focal lengths of the combination, and f2, f2 the focal lengths of the two components, and A the distance between the inner foci of the components, then f = - f,f2/4, f' =fi f27 0 (see Lens).^ If f and f' be the focal lengths of the combination, and f2, f2 the focal lengths of the two components, and A the distance between the inner foci of the components, then f = - f,f2/4, f' =fi f27 0 (see Lens ).

^ In general, the two focal lengths have to be in the ratio somewhere between 1:3 and 1:2.
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^ A, the focal lengths of the objective, and of the eyepiece f2.

is also equal to the distance .F 1 'F 2. The accented f's are always on the image side, whilst the unaccented are on the object side.^ The accented f's are always on the image side, whilst the unaccented are on the object side.

^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

^ In this case the optical tube length equals the distance of the adjacent focal planes of the two systems, which equals the distance of the image-side focus of the objective F 1 ' from the object-side focus of the eyepiece F2.

.From this formula it follows, for example, that one obtains a system of a in.^ From this formula it follows, for example, that one obtains a system of a in.

focal length by compounding two positive systems of 1 in. each, whose focal planes, turned towards one another, are separated by 8 in.
.A microscope objective being made in essentially the same way as a simple microscope, and the front focus of the compound system being situated before the front focus of the objective, the magnification due to the simple system makes the free object distance greater than that obtained with a simple microscope of equal magnification.^ Microscopes are distinguished as simple and compound.

^ The magnification, resulting from the simple microscope of i in.

^ The distance of the object from the nearer focus of the objective is next determined.

.Moreover, this distance between the object and eye is substantially increased in the compound microscope by the stand; the inconveniences, and in certain circumstances also the dangers, to the eye which may arise, for example by warming the object, are also avoided.^ Moreover, this distance between the object and eye is substantially increased in the compound microscope by the stand; the inconveniences, and in certain circumstances also the dangers, to the eye which may arise, for example by warming the object, are also avoided.

^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

^ If the object be represented by two separate points, these points would appear distinct to the normal eye only so long as the distance between them is at the most only 3438 times smaller than their distance from the eye.

.The convenient and rapid change in the magnification obtained by changing the eyepiece or the objective is also a special advantage of the compound form.^ The convenient and rapid change in the magnification obtained by changing the eyepiece or the objective is also a special advantage of the compound form.

^ In the TEM the magnification (focal length) of the objective remains fixed while the focal length of the projector lens is changed to vary magnification.

^ Magnification in the LM is generally changed by switching between different power objective lenses mounted on a rotating turret above the specimen.

.In the commonest compound microscopes, which consist of two positive systems, a real magnified image is produced by the objective.^ He used two special prisms to divided the image produced by the objective.
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^ An image is therefore projected by the ocular from the real magnified image produced by the objective with increased magnification.

^ If we consider the production of the image of an object of this kind by the two positive systems of a compound microscope shown in fig.

.This permits researches which are impossible with the simple microscope.^ The simple microscope permits such vision.

^ This permits researches which are impossible with the simple microscope.

^ Where very short focus simple microscopes are employed, using high magnifications, it is imperative to employ a stand which permits exact focusing and the use of a special illuminating apparatus.

.For example, the real image may be recorded on a photographic plate; it may be measured; it can be physically altered by polarization, by spectrum analysis of the light employed by absorbing layers, &c.^ For example, the real image may be recorded on a photographic plate; it may be measured; it can be physically altered by polarization , by spectrum analysis of the light employed by absorbing layers, &c.

^ Virtual Image : one from which light rays appear to diverge; rays are not in fact concentrated at the position of a virtual image, so that a photographic plate placed at the position of the image is not exposed (by focused rays).

^ A wavelet-based approach may enhance edge detection, but a segmentation methodology must still be employed for real object detection.

.The greatest advantage of the compound microscope is that it represents a larger area, and this much more completely than is possible in the simple form.^ Microscopes are distinguished as simple and compound.

^ The greatest advantage of the compound microscope is that it represents a larger area, and this much more completely than is possible in the simple form.

^ Antony van Leeuwenhoek appears to be the first to succeed in grinding and polishing lenses of such short focus and perfect figure as to render the simple microscope a better instrument for most purposes than any compound microscope then constructed.

.According to the laws of optics it is only possible either to portray a small object near one of the foci of the system with wide pencils, or to produce an image from a relatively large object by correspondingly narrow pencils.^ Since one is therefore forced to use a very small region as the target, it is difficult to produce a good match and its utility is severely restricted.

^ Fortunately, it is possible to improve the image by stopping-down the size of the objective lens so that the light is allowed to pass through only the central portion of the lens.
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^ It is possible that higher frequency forms of radiation could produce holes small enough to be usable as fiducial markers even for electron microscopy.

.The simple microscope is subject to either limitation.^ The simple microscope is subject to either limitation.

^ The simple microscope enlarges the angle of vision, and does not tire the eye when it is arranged so that the image lies in the farthest limit of distinct vision (the punctum remotum).

^ From this it appears that each observer obtains specific advantages from one and the same simple microscope, and also the individual observer can obtain different magnifications by either using different accommodations, or by viewing in passive accommodation.

.As we shall see later, one of the principal functions of the microscope objective is the representation with wide pencils.^ As we shall see later, one of the principal functions of the microscope objective is the representation with wide pencils.

^ The sine-condition is, however, the most important as far as the microscopic representation is concerned, because it must be possible to represent a surfaceelement through the objective by wide cones of rays.

^ For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.

.In that case, however, in the compound microscope a small object may always be represented by means of wider pencils, one of the foci of the objective (not of the collective system) being near it.^ In that case, however, in the compound microscope a small object may always be represented by means of wider pencils, one of the foci of the objective (not of the collective system) being near it.

^ A microscope objective being made in essentially the same way as a simple microscope, and the front focus of the compound system being situated before the front focus of the objective, the magnification due to the simple system makes the free object distance greater than that obtained with a simple microscope of equal magnification.

^ Moreover, this distance between the object and eye is substantially increased in the compound microscope by the stand; the inconveniences, and in certain circumstances also the dangers, to the eye which may arise, for example by warming the object, are also avoided.

.For the eyepiece the other rule holds; the object is represented by narrow pencils, and it is hence possible to subject the relatively great object, viz.^ For the eyepiece the other rule holds; the object is represented by narrow pencils, and it is hence possible to subject the relatively great object, viz.

^ In the case of the brightness of large objects obviously the whole pencil is involved, and hence the clearness is the squares of these values, i.e.

^ Then the object is moved by the micrometer till the image of the other edge is covered by the thread in the eyepiece, and the micrometer is again read.

the magnified real image, to a further representation.

History of the Compound Microscope

.The arrangement of two lenses so that small objects can be seen magnified followed soon after the discovery of the telescope.^ The arrangement of two lenses so that small objects can be seen magnified followed soon after the discovery of the telescope.

^ In the following examples, there are two converging lenses in succession .

^ Object details will only be well seen if the aberration circles are small in comparison.

.The first compound miscroscope (discovered probably by the Middelburg lens-grinders, Johann and Zacharias Janssen about 1590) was a combination of a strong biconvex with a still stronger biconcave lens; it had thus, as well as the first telescope, a negative eyepiece.^ The first compound miscroscope (discovered probably by the Middelburg lens-grinders, Johann and Zacharias Janssen about 1590) was a combination of a strong biconvex with a still stronger biconcave lens; it had thus, as well as the first telescope, a negative eyepiece.

^ John Dollond was first to paten the achromatic lens for the telescope.
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^ The aperture thus controls the ability of the lens to gather information about the object.

.In 1646 Fontana described a microscope which had a positive eyepiece.^ In 1646 Fontana described a microscope which had a positive eyepiece.

.The development of the compound microscope essentially depends on the improvement of the objective; but no distinct improvement was made in its construction in the two centuries following the discovery.^ A microscope is essentially formed by two lenses: the objective and the eyepiece which is also referred to as the ocular.
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^ The third edition of the Britannica was published before the turn of the 19th century and our microscope was undoubtedly made several years later.
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^ Improvement in Eye-pieces and Objectives for Telescopes and Microscopes .

.In 1668 the Italian Divini employed several doublets, i.e. pairs of piano-convex lenses, and his example was followed by Griendl von Ach.^ In the following examples, there are two converging lenses in succession .

^ Usually, these lenses are cemented together in pairs (doublets) and the red and blue colors of the image are made to coincide.
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^ Try to use a plano-convex lens followed by an achromatic doublet, or two equal doublets.
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.But even with such moderate magnification as these instruments permitted many faults were apparent.^ But even with such moderate magnification as these instruments permitted many faults were apparent.

^ Even if the details can be recognized with an apparent magnification of 2', the observation may still be inconvenient.

^ Many of these newer instruments incorporated important innovations.

A microscope, using concave mirrors, was proposed in 1672 by Sir Isaac Newton; and he was succeeded by Barker, R. Smith, B. Martin, D. Brewster, and, above all, Amici. .More recently these catadioptric microscopes were disregarded because they yielded unfavourable results.^ More recently these catadioptric microscopes were disregarded because they yielded unfavourable results.

^ The advantage of light and electron microscopes is that they effectively get the object closer to the eye so a magnified image is obtained and more detail can be discerned.

^ It is our experience that so called "toy microscopes" are a real disaster because they commonly give little more than diffuse images or shadows.
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.From 1830 onwards many improvements were made in the miscroscope objective; these may be best followed from a discussion of the faults of the image.^ From 1830 onwards many improvements were made in the miscroscope objective; these may be best followed from a discussion of the faults of the image.

^ You may want to use these smaller lenses later to see if they can be suitable as objective lens.
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^ Usually, these lenses are cemented together in pairs (doublets) and the red and blue colors of the image are made to coincide.
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Position and Size of Image

.In most microscopic observations the object is mounted on a plane glass plate or slide about o 06 in.^ In most microscopic observations the object is mounted on a plane glass plate or slide about o 06 in.

^ Canada balsam , and covered with a plane glass plate of about o.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

thick, embedded in a liquid such as water, glycerine or .Canada balsam, and covered with a plane glass plate of about o.^ Canada balsam , and covered with a plane glass plate of about o.

^ Abbe's test plate consists of an object carrier on which six cover glasses of exactly determined thickness (between 0.09 mm.

^ In most microscopic observations the object is mounted on a plane glass plate or slide about o 06 in.

008 to 0.006 in. thick, called the cover-slip. .If we consider the production of the image of an object of this kind by the two positive systems of a compound microscope shown in fig.^ We can now understand the ray transmission in the compound microscope, shown in fig.

^ The image produced by a microscope formed of two positive systems (fig.

^ In the commonest compound microscopes, which consist of two positive systems, a real magnified image is produced by the objective.

.13, the objective L1 forms a real magnified image O'Oi'; the object OO l must therefore lie somewhat in front of the front focus F1 of the objective.^ The objective forms a magnified image of the specimen and the eyepiece in turn magnifies this image.
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^ The eyepiece serves to magnifying the image formed by the objective.
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^ An image is therefore projected by the ocular from the real magnified image produced by the objective with increased magnification.

.Let O01=y, O'01' =y', the focal distance of the image F I 'O' =A, and the image-side focal length f l ', then the magnification M =y /y=o/,/1' (3) The distance A is called the " optical tube length."^ For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.

^ Strong systems produce in the proximity of their back focal plane an image of the scale, which can be inspected with a weak auxiliary microscope, and the length of the visible part of the graduation determined.

^ In immersion systems the object-side focal length is greater than the imageside focal length.

.Weak and strong microscope objectives act differently.^ Weak and strong microscope objectives act differently.

^ Strong systems produce in the proximity of their back focal plane an image of the scale, which can be inspected with a weak auxiliary microscope, and the length of the visible part of the graduation determined.

^ When forming an image by a microscope objective it often happens that the transparent media bounding the system have different optical properties.

.Weak systems act like photographic objectives.^ Weak systems act like photographic objectives.

^ Weak and medium microscope objectives work like photographic objectives in episcopic or diascopic projection; in the microscope, however, the projected image is not intercepted on a screen , but p?

^ Weak and strong microscope objectives act differently.

.In this case the optical tube length may be altered within fixed limits without spoiling the image; at the same time the objective magnification M is also altered.^ The magnification number increases then with the optical tube-length and with the diminution of the focal lengths of objective and eyepiece.

^ In this case the optical tube length may be altered within fixed limits without spoiling the image; at the same time the objective magnification M is also altered.

^ When determining the magnification the microscope must be used under exactly the same conditions: neither the length of the tube nor the focal length of the objective may be altered.

.This change is usually effected by mounting the objective and eyepiece on two telescoping tubes, so that by drawing apart or pushing in the tube length is increased or diminished at will.^ The objective and the eyepiece must be mounted in the body tube.
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^ A quick-change objective mounting.

^ The objective and the eyepiece are mounted at either end of the tube as shown in Figure 9.
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.For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.^ For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

^ The sine-condition is, however, the most important as far as the microscopic representation is concerned, because it must be possible to represent a surfaceelement through the objective by wide cones of rays.

This limitation is examined below.
.When forming an image by a microscope objective it often happens that the transparent media bounding the system have different optical properties.^ When forming an image by a microscope objective it often happens that the transparent media bounding the system have different optical properties.

^ The image produced by a microscope formed of two positive systems (fig.

^ I0 is the image formed by the objective lens O, I1 is formed by the first projector lens P1 and I2 by the second projector P2, on the screen.

A series of objectives with short focal lengths are available, which permit the placing of a liquid between the cover-slip and the front lens of the objective; such lenses are known as " immersion systems "; objectives bounded on both sides by air are called " dry systems." The immersion liquids in common use are water, glycerine, cedar-wood oil, monobromnaphthalene, &c. .Immersion systems in which the embedding liquid, coverslip, immersion-liquid and front lens have equal refractive indices are called " homogeneous immersion systems."^ The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index.

^ In immersion systems the immersion liquid is placed between the front lens and apertometer.

^ Immersion systems in which the embedding liquid, coverslip, immersion-liquid and front lens have equal refractive indices are called " homogeneous immersion systems."

.In immersion systems the object-side focal length is greater than the imageside focal length.^ In immersion systems the object-side focal length is greater than the imageside focal length.

^ When the object distance is greater than the focal length, a real, inverted image is formed.

^ The image viewed through the eyepiece appears then to the observer under the angle w", and as with the single microscope tan w" = I /f 2 ' (4) where f' 2 is the image-side focal length of the eyepiece.

.Nothing is altered as to objective magnification, however, as the first surface is plane, and the employment of the immersion means that the value of f l ' 'is unaltered.^ Nothing is altered as to objective magnification, however, as the first surface is plane, and the employment of the immersion means that the value of f l ' 'is unaltered.

^ A X Jo magnification is, however, by no means guaranteed to a myopic eye of - io D by a lens of i in.

^ However, all of Spencer's advertisements of the time mention only the production of fine objectives and not the availability of such a substantial first class stand.
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.If we assume that a normal eye observes the image through the eyepiece, the eyepiece must project a distant image from the real image produced by the objective.^ He used two special prisms to divided the image produced by the objective.
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^ Because the image is a projection through tissue, no depth information is available.

^ Note that in electron microscopy, attenuation of electrons through the specimen produces the image.

.This is the case if the image O'OI' lies in the front focal plane of the eyepiece.^ This is the case if the image O'OI' lies in the front focal plane of the eyepiece.

^ As in the case of the hysteresis of the electromagnets, no precise method of quantifying the effect on the resulting image plane currently exists.

^ An intermediate lens must be placed in the body tube to focus this image on the focal plane of the eyepiece.
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.In this case the optical tube length equals the distance of the adjacent focal planes of the two systems, which equals the distance of the image-side focus of the objective F 1 ' from the object-side focus of the eyepiece F2. The image viewed through the eyepiece appears then to the observer under the angle w", and as with the single microscope tan w" = I /f 2 ' (4) where f' 2 is the image-side focal length of the eyepiece.^ Let f = lens focal length, x o = distance of object in front of the lens, and x i = distance of image behind the lens.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

^ F2 = front focus of eyepiece.

^Er .F FIG. 13. - Ray transmission in compound microscope with a positive ocular.^ We can now understand the ray transmission in the compound microscope, shown in fig.

^ Ray transmission in compound microscope with a positive ocular.

^ The ray transmission, shown in fig.

.L i =objective, L2 L3 = eyepiece of the Ramsden type.^ L i =objective, L2 L3 = eyepiece of the Ramsden type.

^ The Ramsden eyepiece is the most convenient for this because this plane lies in front of the collective lens, and the objective image has not yet been influenced by the eyepiece.

.F l, F1' =objectand image-side foci of objec tive.^ F2' =objectand image-side foci of eyepiece.

^ F 1 ' =objectand image-side foci of objective.

^ F l, F1' =objectand image-side foci of objec tive.

.F2 = front focus of eyepiece.^ F2 = front focus of eyepiece.

^ In this case the optical tube length equals the distance of the adjacent focal planes of the two systems, which equals the distance of the image-side focus of the objective F 1 ' from the object-side focus of the eyepiece F2.

.P'P 1 '= exit pupil of objective.^ P'P 1 '= exit pupil of objective.

^ P'P 1 ' =exit pupil of objective.

^ If a diaphragm lying in the back focal plane of the objective forms the exit pupil for the objective, as in figs.

.P"P 1 " = exit pupil of complete microscope.^ P"P 1 " = exit pupil of complete microscope.

^ So long as the exit pupil is completely filled the brightness of the image will be approximately equal to that of free vision.

^ It is brought about by placing special semicircular diaphragms in the plane of the exit pupil of the microscope.

.D D = diaphragm of field of view.^ DD =diaphragm of the field of view.

^ D D = diaphragm of field of view.

^ DD diaphragm of the field of view.

.To obtain the magnification of the complete microscope we must combine the objective magnification M with the action of the eyepiece.^ ID on the eyepiece the total magnification of the microscope is obtained.

^ To obtain the magnification of the complete microscope we must combine the objective magnification M with the action of the eyepiece.

^ Figure 17 - Microscope for protozoa, notice the objective and the condenser made with an eyepiece for binoculars.
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.If we replace y' in equation (4) by the value given by (3), we obtain tan w"/ y i/f2"=V, (5) the magnification of the complete microscope.^ No method for programmatically querying or setting other microscope parameters (such as magnification, focus value, illumination, etc.

^ If we replace y' in equation (4) by the value given by (3), we obtain tan w"/ y i/f2"=V, (5) the magnification of the complete microscope.

^ Any magnification above the value given by the above formula represents empty magnification , since such magnification leads to no more useful information but rather a magnified blur.

.The magnification therefore equals the power of the joint system.^ The magnification therefore equals the power of the joint system.

^ The resolving power, equal to half the wavelength of the medium (light) used, is roughly 2000 angstroms and produces magnifications up to 2000x.

^ If the objects have a low reflecting power, or if a slightly higher magnification is needed, the lighting can be improved by optical system.

.The magnification is also expressed as the ratio of the apparent size of the object observed through the microscope to the apparent size of the object seen with the naked eye.^ The following chart shows the variation in the sizes of latex sphere calibration standards at different magnifications using the Zeiss 902 microscope in our laboratory.

^ The advantage of light and electron microscopes is that they effectively get the object closer to the eye so a magnified image is obtained and more detail can be discerned.

^ After the thin section of tissue is prepared and placed in the TEM, the microscope is focused and the desired magnification is selected through normal procedures.

.As the conventional distance for clear vision with naked eye is 10 in., it results from fig.^ As the conventional distance for clear vision with naked eye is 10 in., it results from fig.

^ Since this value for the distance of distinct vision is only conventional, it is understood that the capacity of the simple microscope given in (2) holds good only for eyes accustomed to examine small objects io in.

^ So long as the pupil of the observer alone undertakes the regulation of the rays there is no perceptible diminution of illumination in comparison with the naked eye vision.

i that the apparent size is tan w .=3/11. If this value of y be inserted in equation (5), we obtain the magnification number of the compound microscope N =tan w"/ tan w =Ol/f i 'f 2 ' =Vl. (6) The magnification number increases then with the optical tube-length and with the diminution of the focal lengths of objective and eyepiece.^ ID on the eyepiece the total magnification of the microscope is obtained.

^ To obtain the magnification of the complete microscope we must combine the objective magnification M with the action of the eyepiece.

^ A, the focal lengths of the objective, and of the eyepiece f2.

.As with the simple microscope, different observers see differently in the same compound microscope; and hence the magnification varies with the power of accommodation.^ Microscopes are distinguished as simple and compound.

^ As with the simple microscope, different observers see differently in the same compound microscope; and hence the magnification varies with the power of accommodation.

^ The magnification, resulting from the simple microscope of i in.

.The image produced by a microscope formed of two positive systems (fig.^ The image produced by a microscope formed of two positive systems (fig.

^ In the commonest compound microscopes, which consist of two positive systems, a real magnified image is produced by the objective.

^ If we consider the production of the image of an object of this kind by the two positive systems of a compound microscope shown in fig.

.13) is inverted, the objective L 1 tracing from the object 00 1 a real inverted image O'0' 1, and the eyepiece L 2 L 3 maintaining this arrangement.^ L 1 tracing from the object 00 1 a real inverted image O'0' 1, and the eyepiece L 2 L 3 maintaining this arrangement.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ If the object can be seen by using the mirror, the plane mirror must be used; then the actual size of the object and of the image produced by the objective is measured (of the image by a micrometer ocular).

.For many purposes it is immaterial whether the image is inverted or upright; but in some cases an upright image lightens the work, or may be indispensable.^ While this may be appropriate in some cases, in others it may not yield the desired result.

^ It is clear that these approaches work in some instances and may therefore be used to provide a coarse alignment, but an approach that truly considers the shape of the contours is required.

.The simplest microscope which produces an upright image has a negative lens as eyepiece.^ The simplest microscope which produces an upright image has a negative lens as eyepiece.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

^ Strong systems produce in the proximity of their back focal plane an image of the scale, which can be inspected with a weak auxiliary microscope, and the length of the visible part of the graduation determined.

As shown in fig. .14, the real image formed by the objective must fall on the object-side focal plane of the eye _ piece F2, where a normal eye without accommodation can observe it.^ The plane in the object conjugate to the focal plane of the eye-piece is the plane FIG. 14.

^ If we assume that a normal eye observes the image through the eyepiece, the eyepiece must project a distant image from the real image produced by the objective.

^ When the object distance is greater than the focal length, a real, inverted image is formed.

.But as the object-side focus F2 lies behind the eyepiece, the real image is not produced, but the converging pencils from the objective are changed by the eyepiece into parallels; and the point 0 1 in the top of the object y appears at the top to the eye, i.e. the image is upright.^ F2 = front focus of eyepiece.

^ Object points lying out tive eyepiece.

^ But as the object-side focus F2 lies behind the eyepiece, the real image is not produced, but the converging pencils from the objective are changed by the eyepiece into parallels ; and the point 0 1 in the top of the object y appears at the top to the eye, i.e.

.The erection of inverted images by prisms, which was applied to the simple telescope by Porro, and to the binocular i (q.v.^ The erection of inverted images by prisms, which was applied to the simple telescope by Porro, and to the binocular i (q.v.

^ The terrestrial eyepiece (see Telescope ), which likewise ensures an upright image, but which involves an inconvenient lengthening, has also been employed in the binocular microscope.

) by .A. A. Boulanger was employed by K. Bratuscheck in the Greenough L 1 =weak achromatic objective.^ A. A. Boulanger was employed by K. Bratuscheck in the Greenough L 1 =weak achromatic objective.

.L2 = negative eyepiece.^ L2 = negative eyepiece.

.F 1 ' =objectand image-side foci of objective.^ F2' =objectand image-side foci of eyepiece.

^ F 1 ' =objectand image-side foci of objective.

^ F l, F1' =objectand image-side foci of objec tive.

.F2' =objectand image-side foci of eyepiece.^ F l, F1' =objectand image-side foci of objec tive.

^ F2' =objectand image-side foci of eyepiece.

^ F 1 ' =objectand image-side foci of objective.

.P'P 1 ' =exit pupil of objective.^ P'P 1 '= exit pupil of objective.

^ P'P 1 ' =exit pupil of objective.

^ If a diaphragm lying in the back focal plane of the objective forms the exit pupil for the objective, as in figs.

.P "P1' =virtual image of P1P1' =exit pupil of complete microscope.^ P "P1' =virtual image of P1P1' =exit pupil of complete microscope.

^ This image P"P i " is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system.

^ PP1 is the"entrance pupil, P'P1' the exit pupil, and GG the diaphragm.

function of the aperture and the magnification, it can be increased by diminishing the entrance pupil, the magnification remaining unchanged. .A diminution of the aperture, however, would injure a very much more important property, viz.^ A diminution of the aperture, however, would injure a very much more important property, viz.

^ A very marked diminution in illumination occurs, however, when the exit pupil of the instrument is smaller than the pupil of the eye.

^ The pencils producing the real image are very much more acute, and their inclination is the smaller the stronger the magnification.

the resolving power (see below). .With powerful systems, object-points lying quite near the plane focused for would be represented by such large dispersion circles that practically only the points lying in one plane appear simultaneously sharp; and it is only by varying the focus that the object-points lying in other planes can be observed.^ With powerful systems, object-points lying quite near the plane focused for would be represented by such large dispersion circles that practically only the points lying in one plane appear simultaneously sharp; and it is only by varying the focus that the object-points lying in other planes can be observed.

^ Only points lying on the plane focused for can be sharply reproduced in the retina, which acts as object-plane to the retina.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

.The position of the diaphragm limiting the pencils proceeding from the object-points is not constant in the compound microscope.^ The position of the diaphragm limiting the pencils proceeding from the object-points is not constant in the compound microscope.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ When the shortest distance obtained by the highest strain of accommodation is insufficient to recognize small objects, distinct vision is possible at even a shorter distance by placing a very small diaphragm between the eye and the object, the pencils of rays proceeding from the object-points, which otherwise are limited by the pupils of the eye, being thus restricted by the diaphragm.

.In all microscopes the rays are limited, not in the eyepiece, but in the objective, or before the objective when using a condenser.^ In all microscopes the rays are limited, not in the eyepiece, but in the objective, or before the objective when using a condenser .

^ A solid eyepiece for use with microscopes or telescopes..

^ A microscope, using concave mirrors, was proposed in 1672 by Sir Isaac Newton ; and he was succeeded by Barker, R. Smith, B. Martin , D. Brewster, and, above all, Amici.

.If the pencils are limited in the objective, the restriction of the pencil proceeding from the object-point is effected by either the front lens itself, by the boundary of a lens lying behind, by a real diaphragm placed between or behind the objective, or by a diaphragm-image.^ The position of the diaphragm limiting the pencils proceeding from the object-points is not constant in the compound microscope.

^ If the pencils are limited in the objective, the restriction of the pencil proceeding from the object-point is effected by either the front lens itself, by the boundary of a lens lying behind, by a real diaphragm placed between or behind the objective, or by a diaphragm-image.

^ In immersion systems the immersion liquid is placed between the front lens and apertometer.

.The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.^ M is therefore the intersection of the principal rays.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

In fig. 15 the centre of the (After M. v. Rohr.) .FIG. 15. - Entocentric transmission through a microscope objective.^ Hypercentric transmission in a microscope objective.

^ Entocentric transmission through a microscope objective.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

.E=plane focused for; 01 *, 02 * =projections of 0102 on E; Z= centre of projection; P P1=a virtual image of real diaphragm P'P 1 ' with regard to the preceding part of the objective is the entrance pupil.^ PP1 is the"entrance pupil, P'P1' the exit pupil, and GG the diaphragm.

^ P "P1' =virtual image of P1P1' =exit pupil of complete microscope.

^ E=plane focused for; 01 *, 02 * =projections of 0102 on E; Z= centre of projection; P P1=a virtual image of real diaphragm P'P 1 ' with regard to the preceding part of the objective is the entrance pupil.

entrance pupil lies behind the focal plane, and consequently nearer objects appear larger, and farther objects smaller (" entocentric transmission," see below). .If a diaphragm lying in the back focal plane of the objective forms the exit pupil for the objective, as in figs.^ If a diaphragm lying in the back focal plane of the objective forms the exit pupil for the objective, as in figs.

^ The plane in the object conjugate to the focal plane of the eye-piece is the plane FIG. 14.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

.13 and 14, so that its image, the entrance pupil, lies at infinity, all the principal rays in the object-space are parallel to the axis, and we have on the object-side " telecentric " transmission.^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

^ The intersection of the principal rays in this case lies in the middle of the entrance pupil or of the exit pupil.

^ Very often such stereoscopic lenses, owing to faulty construction, give a false idea of space, ignoring the errors which are due to the alteration of the inter-pupillary distance and the visual angles belonging to the principal rays at the object-side (see Binocular Instruments ).

.The size of the imago on the focal plane is always equal to its actual size, and is independent of the distance of the object from the plane focused for.^ The size of the imago on the focal plane is always equal to its actual size, and is independent of the distance of the object from the plane focused for.

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

^ By using an objective micrometer in place of the object, the magnification of the objective can be ascertained and from this the actual size of the object.

.This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

^ After the microscope has been so adjusted that the image of the object to be measured falls exactly in the plane of the cross threads, the object is moved by the micrometer until one edge of the object is exactly covered by a thread.

.To ensure the telecentric transmission, the diaphragm in the back focus of the objective may be replaced by a diaphragm in the front focal plane of the condenser, supposing that uniformly illuminated objects are being dealt with; for in this case all the principal rays in the object-space are transmitted parallel to the axis.^ To ensure the telecentric transmission, the diaphragm in the back focus of the objective may be replaced by a diaphragm in the front focal plane of the condenser, supposing that uniformly illuminated objects are being dealt with; for in this case all the principal rays in the object-space are transmitted parallel to the axis.

^ In most cases a diaphragm regulates the rays.

^ I.23 Definition of principal focus in object space F1 of a lens.

.With uniformly illuminated objects it may happen that the pencil in the object-space may be limited before passing the object, either through the size of the source of light employed or through a diaphragm connected with the illuminating system.^ With uniformly illuminated objects it may happen that the pencil in the object-space may be limited before passing the object, either through the size of the source of light employed or through a diaphragm connected with the illuminating system.

^ The object may be any size.

^ To ensure the telecentric transmission, the diaphragm in the back focus of the objective may be replaced by a diaphragm in the front focal plane of the condenser, supposing that uniformly illuminated objects are being dealt with; for in this case all the principal rays in the object-space are transmitted parallel to the axis.

In fig. 16 (After M. v. Rohr.) .FIG. 16. - Hypercentric transmission in a microscope objective.^ Hypercentric transmission in a microscope objective.

^ Entocentric transmission through a microscope objective.

^ We can now understand the ray transmission in the compound microscope, shown in fig.

E, 02 *, 0* and Z as in fig. .15. PP/ is the entrance pupil.^ PP/ is the entrance pupil.

^ PP 1, which is formed by the lens, limits the aperture of the pencils of rays on the object-side; consequently it is the entrance pupil of the instrument.

the intersection of the principal rays lies in front of the object, and consequently objects in front of the plane focused for will be projected on .E magnified and the objects lying behind it diminished (" hypercentric " transmission).^ E magnified and the objects lying behind it diminished (" hypercentric " transmission).

^ As objects lying near us appear smaller in the case of hypercentric transmission than those lying farther from us, we receive a false impression of the spatial arrangement of the object.

^ In telecentric and hypercentric transmission we obtain a false conception of the spatial arrangement of the objects or their details; in these cases one focusses by turns on the different details, and so obtains an approximate idea of their spatial arrangement.

.It produces a perspective representation entirely opposed to ordinary vision.^ It produces a perspective representation entirely opposed to ordinary vision.

.As objects lying near us appear smaller in the case of hypercentric transmission than those lying farther from us, we receive a false impression of the spatial arrangement of the object.^ As objects lying near us appear smaller in the case of hypercentric transmission than those lying farther from us, we receive a false impression of the spatial arrangement of the object.

^ E magnified and the objects lying behind it diminished (" hypercentric " transmission).

^ In telecentric and hypercentric transmission we obtain a false conception of the spatial arrangement of the objects or their details; in these cases one focusses by turns on the different details, and so obtains an approximate idea of their spatial arrangement.

.Whether the entrance pupil be before or behind the object, in general its position is such that it lies not too near the object, so that the principal rays will have in the object space only trifling inclinations towards one another or are strictly parallel.^ Whether the entrance pupil be before or behind the object, in general its position is such that it lies not too near the object, so that the principal rays will have in the object space only trifling inclinations towards one another or are strictly parallel.

^ The intersection of the principal rays in this case lies in the middle of the entrance pupil or of the exit pupil.

^ Very often such stereoscopic lenses, owing to faulty construction, give a false idea of space, ignoring the errors which are due to the alteration of the inter-pupillary distance and the visual angles belonging to the principal rays at the object-side (see Binocular Instruments ).

.This is specially important, for otherwise pencils from points placed somewhat laterally to the axis arrive with diminished aperture at the image.^ This is specially important, for otherwise pencils from points placed somewhat laterally to the axis arrive with diminished aperture at the image.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ Axial aberration is reduced by distributing the refraction between two lenses; and by placing the two lenses farther apart the errors of the pencils of rays proceeding from points lying outside the axis are reduced.

We see from fig. .13 that the objective's exit pupil P'P1' is portrayed by the positive eyepiece, the image P"P i " limits the pencils P ', double microscope; these inverting prisms permit a convenient adaptation of the instrument to the interpupillary distance of the observer.^ P'P1' is portrayed by the positive eyepiece, the image P"P i " limits the pencils P ', double microscope; these inverting prisms permit a convenient adaptation of the instrument to the interpupillary distance of the observer.

^ P "P1' =virtual image of P1P1' =exit pupil of complete microscope.

^ The mechanical arrangement of the eyepiece is such that the distance of the two exit pupils can be adjusted to the interpupillary distance.

.Double microscopes, which produce a correct impression of the solidity of the object, must project upright images.^ Double microscopes, which produce a correct impression of the solidity of the object, must project upright images.

^ The simplest microscope which produces an upright image has a negative lens as eyepiece.

^ In the oldest microscope by Cherubin d'Orleans the observer receives a pseudoscopic impression in consequence of the reversed image.

.The terrestrial eyepiece (see Telescope), which likewise ensures an upright image, but which involves an inconvenient lengthening, has also been employed in the binocular microscope.^ The simplest microscope which produces an upright image has a negative lens as eyepiece.

^ The terrestrial eyepiece (see Telescope ), which likewise ensures an upright image, but which involves an inconvenient lengthening, has also been employed in the binocular microscope.

^ Double microscopes, which produce a correct impression of the solidity of the object, must project upright images.

Regulation of the Rays. - .Weak and medium microscope objectives work like photographic objectives in episcopic or diascopic projection; in the microscope, however, the projected image is not intercepted on a screen, but p?^ Weak and medium microscope objectives work like photographic objectives in episcopic or diascopic projection; in the microscope, however, the projected image is not intercepted on a screen , but p?

^ Weak systems act like photographic objectives.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

p; a real image in air is formed. This ---? `' must lie in the front focal plane of the eyepiece if we retain the supposition .IT/ that it is to be viewed by a normal 0, p F, eye with passive accommodation.^ IT/ that it is to be viewed by a normal 0, p F, eye with passive accommodation.

^ F2, where a normal eye without accommodation can observe it.

^ From this it appears that each observer obtains specific advantages from one and the same simple microscope, and also the individual observer can obtain different magnifications by either using different accommodations, or by viewing in passive accommodation.

.The plane in the object conjugate to the focal plane of the eye-piece is the plane FIG. 14. - Ray transfocused for; and all points in it are mission in compound sharply portrayed (a perfect objective microscope with a negabeing assumed).^ We can now understand the ray transmission in the compound microscope, shown in fig.

^ The plane in the object conjugate to the focal plane of the eye-piece is the plane FIG. 14.

^ Ray transfocused for; and all points in it are mission in compound sharply portrayed (a perfect objective microscope with a negabeing assumed).

.Object points lying out tive eyepiece.^ A real lens takes each object point and spreads it out into a circular disk ( Airy disk ) in the image plane whose diameter depends on the angular aperture of the lens.

of the focal plane, on the other hand, are projected as circles of confusion on the plane focused for, the centre of the entrance pupil being the centre of projection and the circles of confusion constituting, with the points of the focal plane, the object-side .imago. As the pencils used in the representations are of wide aperture on the object-side, only such points as are proportionately very near the focal plane can produce such small dispersion circles on the plane focused for, that they, so far as the objectiveand eyepiece-magnification permit, appear as points to the eye.^ Points of a small object (compared with the focus of the objective) send to the objective wide pencils.

^ Only points lying on the plane focused for can be sharply reproduced in the retina, which acts as object-plane to the retina.

^ The plane in the object conjugate to the focal plane of the eye-piece is the plane FIG. 14.

.It follows that the depth of definition of the microscope is in general very trifling.^ It follows that the depth of definition of the microscope is in general very trifling.

^ Very powerful simple microscopes have hardly any depth of definition so that in fact only points lying in one plane can be seen sharply with one focusing.

.As it is entirely a proceeding from the eyepiece.^ As it is entirely a proceeding from the eyepiece.

.This image P"P i " is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system.^ This image P"P i " is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system.

^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ PP1 is the"entrance pupil, P'P1' the exit pupil, and GG the diaphragm.

.As the exit pupil ['P i ' for the objective lies before the front focus of the eyepiece, generally at some distance and near the objective, the eyepiece projects a real image from it behind its image-side focus, so that if this point is accessible it is the exit pupil P"P i ". If, e.g. in the object-space the objective has telecentric transmission, the exit pupil must coincide with the back focal plane of the combined system, and it always lies behind the image-side focus of the eyepiece.^ Let f = lens focal length, x o = distance of object in front of the lens, and x i = distance of image behind the lens.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

^ F2 = front focus of eyepiece.

.The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

^ Here also the exit-pupil is accessible to the eye and through it the whole field can be seen by moving the head and eye.

.We can now understand the ray transmission in the compound microscope, shown in fig.^ We can now understand the ray transmission in the compound microscope, shown in fig.

^ Ray transmission in compound microscope with a positive ocular.

^ The ray transmission, shown in fig.

.13. Points of a small object (compared with the focus of the objective) send to the objective wide pencils.^ Points of a small object (compared with the focus of the objective) send to the objective wide pencils.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ But as the object-side focus F2 lies behind the eyepiece, the real image is not produced, but the converging pencils from the objective are changed by the eyepiece into parallels ; and the point 0 1 in the top of the object y appears at the top to the eye, i.e.

.The diaphragm limiting them, i.e. the entrance pupil, is placed so that the principal rays are either parallel or slightly inclined.^ When the shortest distance obtained by the highest strain of accommodation is insufficient to recognize small objects, distinct vision is possible at even a shorter distance by placing a very small diaphragm between the eye and the object, the pencils of rays proceeding from the object-points, which otherwise are limited by the pupils of the eye, being thus restricted by the diaphragm.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

^ PP1 is the"entrance pupil, P'P1' the exit pupil, and GG the diaphragm.

.The pencils producing the real image are very much more acute, and their inclination is the smaller the stronger the magnification.^ The factors are electromagnet hysteresis (producing an altered magnification), focus variation (inducing an image enlargement and rotation), and variation in stage control (producing an imprecise movement).

^ Note that with this more traditional method of validation, values are more precise with higher magnification due to image quantization effects.

^ Note: Measurements should be more accurate at higher magnifications, due to smaller quantization error.

.The eyepiece, which by means of narrow pencils represents the relatively large real image at infinity, transmits from all points of this real image parallel pencils, whereby the inclination of the principal rays becomes further increased.^ Its purpose in a microscope is by means of narrow cones of rays to represent at infinity the real magnified image which the objective produces.

^ The eyepiece, which by means of narrow pencils represents the relatively large real image at infinity, transmits from all points of this real image parallel pencils, whereby the inclination of the principal rays becomes further increased.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

.The point of intersection, i.e. the centre of the exit pupil, is accessible to the eye of the observer.^ A very marked diminution in illumination occurs, however, when the exit pupil of the instrument is smaller than the pupil of the eye.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

.In the case of the negative eyepiece, on the other hand, the divergence of the principal rays through the eyepiece is also further augmented, but their point of intersection is not accessible to the eye.^ M is therefore the intersection of the principal rays.

^ In the case of the negative eyepiece, on the other hand, the divergence of the principal rays through the eyepiece is also further augmented, but their point of intersection is not accessible to the eye.

^ The centre of the entrance pupil is the point of intersection of the principal rays; and it is therefore determinative for the perspective representation on the plane focused for.

.This property shows the superiority of the collective eyepiece over the dispersive.^ This property shows the superiority of the collective eyepiece over the dispersive.

.The increase of the inclination of the principal rays, which arises with the microscope, influences the perception of the relief of the object.^ The increase of the inclination of the principal rays, which arises with the microscope, influences the perception of the relief of the object.

^ Moreover, this distance between the object and eye is substantially increased in the compound microscope by the stand; the inconveniences, and in certain circumstances also the dangers, to the eye which may arise, for example by warming the object, are also avoided.

^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

In entocentric transmission this phenomenon appears in general as in the case of the contemplation of perspective representations at a too short distance, the objects appearing flattened. .Although in the case of the spatial comprehension of a perspective representation experience plays a large part, in observing through a microscope it does not count, or only a little, for the object is presumably quite unknown.^ Note that this also means that part of the lens field ("pre-field") is on the front side of the object and affects the electron beam before it passes through the object.

^ Engineers have allegedly narrowed down the source of the problem in "specific cases," although specific details remain unknown....
  • Megite Technology News: What's Happening Right Now 1 February 2010 1:54 UTC www.megite.com [Source type: General]

^ The microscopes at Technical Instruments include a large number of instruments that are not yet part of this inventory.
  • Microscope Antique Collection 23 January 2010 9:54 UTC www.techinst.com [Source type: FILTERED WITH BAYES]

.In telecentric and hypercentric transmission we obtain a false conception of the spatial arrangement of the objects or their details; in these cases one focusses by turns on the different details, and so obtains an approximate idea of their spatial arrangement.^ In telecentric and hypercentric transmission we obtain a false conception of the spatial arrangement of the objects or their details; in these cases one focusses by turns on the different details, and so obtains an approximate idea of their spatial arrangement.

^ As objects lying near us appear smaller in the case of hypercentric transmission than those lying farther from us, we receive a false impression of the spatial arrangement of the object.

^ In entocentric transmission this phenomenon appears in general as in the case of the contemplation of perspective representations at a too short distance, the objects appearing flattened.

.While the limiting of the pencil is almost always effected by the objective, the limiting of the field of view is effected by the eyepiece, and indeed it is carried out by a real diaphragm DD arranged in the plane of the real image O'O 1 (fig.^ DD =diaphragm of the field of view.

^ While the limiting of the pencil is almost always effected by the objective, the limiting of the field of view is effected by the eyepiece, and indeed it is carried out by a real diaphragm DD arranged in the plane of the real image O'O 1 (fig.

^ D D = diaphragm of field of view.

13) projected from the objective. .The entrance window is then the real image of this diaphragm projected by the objective in the surface conjugate to the plane focused for, and the exit window is the image projected by the eyepiece; this happens with the image of the object lying at infinity.^ When observing with such an eyepiece, care must be taken that the real image of the object lies in the plane of the crossthreads, i.e.

^ If a diaphragm lying in the back focal plane of the objective forms the exit pupil for the objective, as in figs.

^ The entrance window is then the real image of this diaphragm projected by the objective in the surface conjugate to the plane focused for, and the exit window is the image projected by the eyepiece; this happens with the image of the object lying at infinity.

.The result must be that the field of view exhibits a sharp border.^ The result must be that the field of view exhibits a sharp border.

^ In this case also the illumination must fall to zero by the vignetting of the pencils coming from objects at the margin of the field of view.

.In the case of the dispersive eyepiece, on the contrary, no sharply limited field can arise, but vignetting must occur.^ In the case of the dispersive eyepiece, on the contrary, no sharply limited field can arise, but vignetting must occur.

^ In this case also the illumination must fall to zero by the vignetting of the pencils coming from objects at the margin of the field of view.

^ The placing of the analyser near the objective has the advantage that the field of view is not restricted, as is the case if the analyser .is used above the eyepiece.

Illumination

.The dependence of the clearness of the image on the aperture of the system, i.e. on the angular aperture of the image-producing pencil, holds for all instruments.^ The dependence of the clearness of the image on the aperture of the system, i.e.

^ To fully utilize the aperture of the system all dispersing rays in the object-space of the objective must be retained in the imagespace of the illuminating system.

^ In dark field illumination care has to be taken that no direct rays reach the objective, and hence a good dark field illumination can be produced if the condenser system has a larger aperture than the objective.

.The brightnesses of image points in a median section of the pencil are proportional to the aperture of the lens, supposing that the rays are completely reunited.^ The brightnesses of image points in a median section of the pencil are proportional to the aperture of the lens, supposing that the rays are completely reunited.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

^ The selection of the rays emerging from the lens and actually employed in forming the image is undertaken by the pupil of the eye which, in this case, is consequently the exit pupil of the instrument.

.This is valid so long as the pencil is in air; but if, on the other hand, the pencil passes from air through a plane surface into an optically denser medium, e.g. water or glass, the pencil becomes more acute and the aperture smaller.^ This is valid so long as the pencil is in air; but if, on the other hand, the pencil passes from air through a plane surface into an optically denser medium, e.g.

^ On the other hand, as the observer recedes from the object, the apparent size, and also the image on the retina diminishes; details become more and more confused, and gradually, after a while, disappear altogether, and ultimately the external configuration of the object as a whole is no longer recognizable.

^ In immersion-systems of such considerable aperture no medium of smaller refractive index than the immersion liquid may be placed between the surface of the front lens and the object, as otherwise total reflection would occur.

.But since no rays are lost in this transmission (apart from the slight loss due to reflection) the brightness of the image point in the water is as large as that in air, although the apertures have become less.^ But since no rays are lost in this transmission (apart from the slight loss due to reflection) the brightness of the image point in the water is as large as that in air, although the apertures have become less.

^ Since in these systems the sine-condition can be fulfilled for several colours, the quality of the images of points beyond the axis is better.

^ In addition to a considerable increase in brightness the losses due to reflection are avoided; losses which arise in passing to the back surface of the cover-slip and to the front surface of the front lens.

Fig. .17 shows a pencil in air, A, dispersing in water, W, from the semiaperture u 1, or a pencil in water dispersing in air from the semiaperture u2. If the value of the clearness in air be taken as sin u1, then by the law of refraction N =sin u l /sin u2, the value for the clearness in water is N sin u 2. This rule is general.^ If the value of the clearness in air be taken as sin u1, then by the law of refraction N =sin u l /sin u2, the value for the clearness in water is N sin u 2.

^ The value n sin u equals the numerical aperture A, where n is the refractive index of the immersion-liquid, and u is the semi-aperture on the object-side.

^ In the case of the brightness of large objects obviously the whole pencil is involved, and hence the clearness is the squares of these values, i.e.

.The value of the clearness of an image-point in a median section is the sine of the semi-aperture of the pencil multiplied with the refractive index of the medium.^ The dependence of the clearness of the image on the aperture of the system, i.e.

^ The value of the clearness of an image-point in a median section is the sine of the semi-aperture of the pencil multiplied with the refractive index of the medium.

^ In the case of the brightness of large objects obviously the whole pencil is involved, and hence the clearness is the squares of these values, i.e.

.An illustration of this principle is the immersion experiment.^ An illustration of this principle is the immersion experiment.

.A view taken under water from the point 0 (fig.^ A view taken under water from the point 0 (fig.

18) sees not only the whole horizon, but also a part of the bed of the sea. .The whole field of view in air of 180° is compressed to one of 97.5° in water.^ The whole field of view in air of 180° is compressed to one of 97.5° in water.

.The rays from 0 which have a greater inclination to the vertical than 48.75° cannot come out into the air, but are totally reflected.^ The rays from 0 which have a greater inclination to the vertical than 48.75° cannot come out into the air, but are totally reflected.

^ But, owing to the various partial reflections which the illuminating cone of rays undergoes when traversing the surfaces of the lenses, a portion of the light comes again into the preparation, and into the eye of the observer, thus veiling the image.

^ By the supplementary use of one of Wenham's prisms every ray is analysed into a more powerful refracted and a weaker reflected one.

.If pencils proceed from media of high optical density to media of low density, and have a semi-aperture greater than the critical angle, total reflection occurs; in such cases no plane surface can be employed, hence front lenses have small radii of curvature in order to permit the wide pencils to reach the air (see fig.^ He also showed the influence of the cover-slip on pencils of such wide aperture.

^ If pencils proceed from media of high optical density to media of low density, and have a semi-aperture greater than the critical angle, total reflection occurs; in such cases no plane surface can be employed, hence front lenses have small radii of curvature in order to permit the wide pencils to reach the air (see fig.

^ In immersion-systems of such considerable aperture no medium of smaller refractive index than the immersion liquid may be placed between the surface of the front lens and the object, as otherwise total reflection would occur.

.19, in which P is the preparation, 0 the object-point in it, D the cover slip, I the immersing fluid, and L the front lens).^ P is the preparation, 0 the object-point in it, D the cover slip, I the immersing fluid, and L the front lens).

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

.The function n sin u = A, for the microscope, has been called by Abbe the numerical aperture. In dry-systems only the sine of the semi-aperture is concerned; in immersion-systems it is the product of the refractive index of the immersion-liquid and the sine of the object-side semi-aperture.^ The function n sin u = A, for the microscope, has been called by Abbe the numerical aperture.

^ The sine of this angle is the numerical aperture for dry lenses.

^ The value n sin u equals the numerical aperture A, where n is the refractive index of the immersion-liquid, and u is the semi-aperture on the object-side.

.In the case of the brightness of large objects obviously the whole pencil is involved, and hence the clearness is the squares of these values, i.e. sin e u or n 2 sin' u. As the semiaperture of a pencil proceeding from an object point cannot exceed 90°, the numerical aperture of a dry-system cannot be greater than I. On the other hand, in immersion-systems the numerical aperture can almost amount to the refractive index, for A=n sin u<n. Dry systems of o 98 numerical aperture, water immersion (n =1.33) from A =I 25, oil immersion (n =1.51) from A =1.40, and even a-bromnaphthalene immersions (n =I-65) from A =1.60, are available.^ In the case of the brightness of large objects obviously the whole pencil is involved, and hence the clearness is the squares of these values, i.e.

^ With the best immersion-system, having a numerical aperture of 1.6, details of the size o.

^ In immersion systems the object-side focal length is greater than the imageside focal length.

.In immersion-systems of such considerable aperture no medium of smaller refractive index than the immersion liquid may be placed between the surface of the front lens and the object, as otherwise total reflection would occur.^ Forms a real inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens.

^ Spherical refracting surfaces act as lenses for paraxial rays which are those rays that pass close to the principal axis of the lens.

^ Let f = lens focal length, x o = distance of object in front of the lens, and x i = distance of image behind the lens.

.This is especially inconvenient in the case of the a-bromnaphthalene immersion.^ This is especially inconvenient in the case of the a-bromnaphthalene immersion.

.As the embedding and immersing liquids must have equal refractive indexes, one must use a-bromnaphthalene for embedding; but this substance destroys organic preparations, so that one can employ this immersion-system only for examining inorganic materials, e.g. fine diatoms.^ As the embedding and immersing liquids must have equal refractive indexes, one must use a-bromnaphthalene for embedding; but this substance destroys organic preparations, so that one can employ this immersion-system only for examining inorganic materials, e.g.

^ Immersion systems in which the embedding liquid, coverslip, immersion-liquid and front lens have equal refractive indices are called " homogeneous immersion systems."

^ The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index.

.In immersion-systems a very much greater aggregate of rays is used in the representation than is possible in dry-systems.^ In immersion-systems a very much greater aggregate of rays is used in the representation than is possible in dry-systems.

^ In dark field illumination care has to be taken that no direct rays reach the objective, and hence a good dark field illumination can be produced if the condenser system has a larger aperture than the objective.

^ In immersion systems the object-side focal length is greater than the imageside focal length.

.In addition to a considerable increase in brightness the losses due to reflection are avoided; losses which arise in passing to the back surface of the cover-slip and to the front surface of the front lens.^ In addition to a considerable increase in brightness the losses due to reflection are avoided; losses which arise in passing to the back surface of the cover-slip and to the front surface of the front lens.

^ In addition, weighting factors are available to give increased consideration to larger objects when appropriate.

^ Spherical refracting surfaces act as lenses for paraxial rays which are those rays that pass close to the principal axis of the lens.

.THE Physical Theory In order to fully understand the representation in the microscope, the process must be investigated according to the wavetheory, especially in considering the representation of objects or object details having nearly the size of a wave-length.^ THE Physical Theory In order to fully understand the representation in the microscope, the process must be investigated according to the wavetheory, especially in considering the representation of objects or object details having nearly the size of a wave -length.

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

^ As we saw above, the apparent size of a detail of an object must be greater than the angular range of vision, i.e.

.The rectilinear rays, which we have considered above, but which have no real existence, are nothing but the paths in which the light waves are transmitted.^ The rectilinear rays, which we have considered above, but which have no real existence, are nothing but the paths in which the light waves are transmitted.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

^ Ideal verses real lenses: Lenses are used to bend rays of light or electrons so they are deflected in a predictable way from their original paths.

.According to Huygens's principle (see Diffraction) each aether particle, set vibrating by an incident wave, can itself act as a new centre of excitement, emitting a spherical wave; and similarly each particle on this wave itself produces wave systems.^ According to Huygens's principle (see Diffraction ) each aether particle, set vibrating by an incident wave, can itself act as a new centre of excitement, emitting a spherical wave; and similarly each particle on this wave itself produces wave systems.

^ According to the phase of the vibrations at this common point, the waves mutually strengthen or weaken their action, and there arises greater clearness or obscurity.

^ All systems which are emitted from a single source can by a suitable optical device be directed that they simultaneously influence one and the same aether particle.

.All systems which are emitted from a single source can by a suitable optical device be directed that they simultaneously influence one and the same aether particle.^ All systems which are emitted from a single source can by a suitable optical device be directed that they simultaneously influence one and the same aether particle.

^ First, while the registration of a single object may exhibit the "leaning tower" effect mentioned above, when registering a section comprised of many objects, the probability of all objects projecting in the same direction, at the same rate, is exceedingly low.

^ Even if local bundles of fibers project in the same direction, other objects in the area may provide a suitable frame of reference.

.According to the phase of the vibrations at this common point, the waves mutually strengthen or weaken their action, and there arises greater clearness or obscurity.^ According to the phase of the vibrations at this common point, the waves mutually strengthen or weaken their action, and there arises greater clearness or obscurity.

^ The phase of a wave (usually expressed as a fraction of the wavelength or in degrees) is the position of a crest relative to some arbitrary point.

.This phenomenon is called interference (q.v.^ This phenomenon is called interference (q.v.

). .E. Abbe applied the Fraunhofer diffraction phenomena to the explanation of the representation in the microscope of uniformly illuminated objects.^ E. Abbe applied the Fraunhofer diffraction phenomena to the explanation of the representation in the microscope of uniformly illuminated objects.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ The Fraunhofer diffraction phenomena, which take place in the 0 FIG. 18.

.If a grating is placed as object before the microscope objective, Abbe showed that in the image there is intermittent clear and dark banding only, if at least two consecutive diffraction spectra enter into the objective and contribute towards the image.^ If a grating is placed as object before the microscope objective, Abbe showed that in the image there is intermittent clear and dark banding only, if at least two consecutive diffraction spectra enter into the objective and contribute towards the image.

^ At least two successive diffraction maxima must be admitted through the objective for there to be any image of the objects.

^ The resemblance is greater the more diffraction spectra enter the objective.

.If the illuminating pencil is parallel to the axis of the microscope objective, the illumination is said to be direct.^ If the illuminating pencil is parallel to the axis of the microscope objective, the illumination is said to be direct.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ In dark field illumination care has to be taken that no direct rays reach the objective, and hence a good dark field illumination can be produced if the condenser system has a larger aperture than the objective.

.If in this case the aperture of the objective be so small, or the diffraction spectra lie so far from each other, that only the pencil parallel to the axis, i.e. the spectrum of zero order, can be admitted, no trace is generally found of the image of the grating.^ Diffraction at this aperture gives rise to a series of fringes, which surround the image formed of the point source.

^ Diffraction also limits the resolving power of the microscope since the image point produced by a lens is a diffraction image of the opening of the lens or the aperture restricting the effective opening of the lens (Fig.

^ Thus, a beam of electrons in parallel paths parallel to the axis of the lens will be focused to an image point on the axis which represents the second (back) focal point of the lens ( f 2 ).

.If, in addition to the principal maximum, the maximum of 1st order is admitted, the banding is distinctly seen, although the image does not yet accurately resemble the object.^ If, in addition to the principal maximum, the maximum of 1st order is admitted, the banding is distinctly seen, although the image does not yet accurately resemble the object.

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

^ Objects at different distances, however, are not seen distinctly simultaneously, but in succession.

.The resemblance is greater the more diffraction spectra enter the objective.^ The resemblance is greater the more diffraction spectra enter the objective.

^ As was seen when discussing the physical theory, the minute details of the object cause diffractions, and can only be examined if the objective can take up at least two consecutive diffraction spectra.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

.From the Fraunhofer formula I =X/n sin a one can immediately deduce the limit to the diffraction constant I, so that the banding by an objective of fixed numerical aperture can be perceived.^ From the Fraunhofer formula I =X/n sin a one can immediately deduce the limit to the diffraction constant I, so that the banding by an objective of fixed numerical aperture can be perceived.

^ If microscopic preparations are observed by diffused daylight or by the more or less white light of the usual artificial sources, then an objective of fixed numerical aperture will only represent details of a definite fineness.

^ The resolving power of an objective depends on its numerical aperture.

.The value n sin u equals the numerical aperture A, where n is the refractive index of the immersion-liquid, and u is the semi-aperture on the object-side.^ The value n sin u equals the numerical aperture A, where n is the refractive index of the immersion-liquid, and u is the semi-aperture on the object-side.

^ In dry-systems only the sine of the semi-aperture is concerned; in immersion-systems it is the product of the refractive index of the immersion-liquid and the sine of the object-side semi-aperture.

^ As the semiaperture of a pencil proceeding from an object point cannot exceed 90°, the numerical aperture of a dry-system cannot be greater than I. On the other hand, in immersion-systems the numerical aperture can almost amount to the refractive index, for A=n sin u Dry systems of o 98 numerical aperture, water immersion (n =1.33) from A =I 25, oil immersion (n =1.51) from A =1.40, and even a-bromnaphthalene immersions ( n =I-65 ) from A =1.60, are available.

.For microscopy the Fraunhofer formula is best written S =X/A. This expresses I as the resolving power in the case of direct lighting.^ For microscopy the Fraunhofer formula is best written S =X/A. This expresses I as the resolving power in the case of direct lighting .

^ The resolving power, equal to half the wavelength of the medium (light) used, is roughly 2000 angstroms and produces magnifications up to 2000x.

^ As the microscopist usually estimates the resolving power according to the aperture with ordinary day-light, Kohler introduced the " relative resolving power " for ultra-violet light.

.All details of the object so resolved are perceived, if two diffraction maxima can be passed through the objective, so that the character of the object is seen in the image, even if an exact resemblance has not yet been attained.^ At least two successive diffraction maxima must be admitted through the objective for there to be any image of the objects.

^ All details of the object so resolved are perceived, if two diffraction maxima can be passed through the objective, so that the character of the object is seen in the image, even if an exact resemblance has not yet been attained.

^ The arrangement of two lenses so that small objects can be seen magnified followed soon after the discovery of the telescope.

The Fraunhofer diffraction phenomena, which take place in the 0 FIG. 18.
back focal plane of the objective, can be conveniently seen with the naked eye by removing the eyepiece and looking into the tube, or better by focusing a weak .auxiliary microscope on the back focal plane of the objective.^ If one focuses an auxiliary microscope, carried in the inner tube, on the image situated in the back focal plane of the objective of a distant object, and then on the dust particles lying on a slide pressed against the end of the outer tube, the displacement of the auxiliary microscope gives the distance of the back focal plane of the objective from the end of the outer tube.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

^ Strong systems produce in the proximity of their back focal plane an image of the scale, which can be inspected with a weak auxiliary microscope, and the length of the visible part of the graduation determined.

.If one has, e.g. in the case of a grating, telecentric transmission on the object-side, and in the front focal plane of the illuminating system a small circular aperture is arranged, then by the help of the auxiliary microscope one sees in the middle of the back focal plane the round white image 0 (fig.^ The dependence of the clearness of the image on the aperture of the system, i.e.

^ The plane in the object conjugate to the focal plane of the eye-piece is the plane FIG. 14.

^ The image produced by a microscope formed of two positive systems (fig.

.20) and to the right and left the diffraction spectra, the images of different colours partially overlapping.^ Too much light is useless for observing delicately coloured or colourless preparations, whose parts only become visible as a result of slight differences of diffraction.

^ By passing this template over the image in a top-down, left-to-right manner, each pixel of the image will be assigned a different color.

^ This can be done by cutting off the chief maximum and using only the diffracted spectra for producing the image.

.If a resolvable grating is considered, the diffraction phenomenon has the appearance shown in fig.^ If a resolvable grating is considered, the diffraction phenomenon has the appearance shown in fig.

^ If this object be viewed by the objective, so that at least the diffraction spectra of 1st order pass the finer divisions, then the corresponding diffraction phenomenon in the back focal plane of the objective has the appearance shown in fig.

^ If we consider the production of the image of an object of this kind by the two positive systems of a compound microscope shown in fig.

21.
It is possible to almost double the resolving power, as in the case FIG. 21. FIG. 22. FIG. 23 FIG. 24. FIG. 25. FIG 26.
.(From Abbe, Theorie der Bilderzeugung Mikroskop.^ (From Abbe, Theorie der Bilderzeugung Mikroskop.

)
of direct lighting, so that a banding of double the fineness can be perceived, by inclining the illuminating pencil to the axis; this is controlled by moving the diaphragm laterally. If the obliquity of illumination be so great that the principal maximum passes through the outermost edge of the objective, while a spectrum of 1st order passes the opposite edge, so that in the back focal plane the diffraction phenomenon shown in fig. 22 arises, banding is still to be seen. .The resolution in the case of oblique illumination is given by the formula 6=X/2A. Reverting to fig.^ The resolution in the case of oblique illumination is given by the formula 6=X/2A. Reverting to fig.

^ Supposing, however, there is oblique illumination, then formula (5) can always be applied to determine the magnifying power attainable with at least one objective.

^ The magnification and magnifying number which are most necessary for a microscope with an objective of a given aperture can then be calculated from the formulae: V4 = 2A tan 4'/X; N4 = 2Al tan 4'/A. .

.13, we suppose that a diffracting particle of such fineness is placed at 0 that the diffracted pencils of the 1st order make an angle w with the axis; the principal maximum of the Fraunhofer diffraction phenomena lies in F' 1; and the two diffraction maxima of the 1st order in P' and P' 1. The waves proceeding from this point are united in the point 0'. Suppose that a well corrected objective is employed.^ Suppose that a well corrected objective is employed.

^ The Fraunhofer diffraction phenomena, which take place in the 0 FIG. 18.

^ The waves proceeding from this point are united in the point 0'.

The image 0' of the point 0 is then the interference effect of all waves proceeding from the exit pupil of the objective P1P1'.
.Abbe showed that for the production of an image the diffraction maxima must lie within the exit pupil of the objective.^ Abbe showed that for the production of an image the diffraction maxima must lie within the exit pupil of the objective.

^ This image P"P i " is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system.

^ If we assume that a normal eye observes the image through the eyepiece, the eyepiece must project a distant image from the real image produced by the objective.

.In the silvering of a glass plate lines are ruled as shown in fig.^ In the silvering of a glass plate lines are ruled as shown in fig.

^ Still more strikingly is this phenomenon shown by Abbe's diffraction plate (fig.

^ The cover glasses are silvered on their under surfaces, and in the silvering fine lines are drawn; these lines form the test object.

23, one set traversing the field while the intermediate set extends only half-way across. If this object be viewed by the objective, so that at least the diffraction spectra of 1st order pass the finer divisions, then the corresponding diffraction phenomenon in the back focal plane of the objective has the appearance shown in fig. .21, while the diffraction figure corresponding to the coarser ruling appears as given in fig.^ A good description and figure of this instrument is given as fig.
  • Transylvania University Philosophical Museum - PhilosophicalApparatus 23 January 2010 9:54 UTC homepages.transy.edu [Source type: FILTERED WITH BAYES]

^ If now the spectrum of Est order of the larger division be cut out from the diffraction figure, as is shown in fig.

^ This quadrant, although the name plate is missing, appears to resemble closely the one figured in plate CCCXLI fig.
  • Transylvania University Philosophical Museum - PhilosophicalApparatus 23 January 2010 9:54 UTC homepages.transy.edu [Source type: FILTERED WITH BAYES]

.20. If one cuts out by a diaphragm in the back focal plane of the objective all diffraction spectra except the principal maximum, one sees in the image a field divided into two halves, which show with different clearness, but no banding.^ He used two special prisms to divided the image produced by the objective.
  • Microscope Antique Collection 23 January 2010 9:54 UTC www.techinst.com [Source type: FILTERED WITH BAYES]

^ If a diaphragm lying in the back focal plane of the objective forms the exit pupil for the objective, as in figs.

^ The cutting off of the chief maximum can be effected by a suitable diaphragm in the back focal plane of the objective.

.By choosing a somewhat broader diaphragm, so that the spectra of 1st order can pass the larger division, there arises in the one half of the field of view the image of the larger division, the other half being clear without any such structure.^ DD =diaphragm of the field of view.

^ By choosing a somewhat broader diaphragm, so that the spectra of 1st order can pass the larger division, there arises in the one half of the field of view the image of the larger division, the other half being clear without any such structure.

^ D D = diaphragm of field of view.

.By using a yet wider diaphragm which admits the spectra of 2nd order of the larger division and also the spectra of 1st order of the fine division, an image is obtained which is similar to the object, i.e. it shows bands one half a division double as fine as on the other.^ By using a yet wider diaphragm which admits the spectra of 2nd order of the larger division and also the spectra of 1st order of the fine division, an image is obtained which is similar to the object, i.e.

^ By choosing a somewhat broader diaphragm, so that the spectra of 1st order can pass the larger division, there arises in the one half of the field of view the image of the larger division, the other half being clear without any such structure.

^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

.If now the spectrum of Est order of the larger division be cut out from the diffraction figure, as is shown in fig.^ If now the spectrum of Est order of the larger division be cut out from the diffraction figure, as is shown in fig.

^ Still more strikingly is this phenomenon shown by Abbe's diffraction plate (fig.

^ We can now understand the ray transmission in the compound microscope, shown in fig.

.24, an image is obtained which over the whole field shows a similar division (fig.^ Lister showed that a combination of lenses can be achromatic for only two points on the axis, and therefore that the single systems must be so arranged that the aplanatic (virtual) image-point 0' (fig.

^ By using a yet wider diaphragm which admits the spectra of 2nd order of the larger division and also the spectra of 1st order of the fine division, an image is obtained which is similar to the object, i.e.

^ By a correct choice of the focal length of the illuminating lens in relation to the focal length of the mirror, it is possible to choose the size of the image of the source of light so that the whole object-field is uniformly lighted.

.25), although in the one half of the object the represented banding does not occur.^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ It consists in half of a short focused parabolic mirror, which concentrates all the light coming from the one side on to the object.

^ Although the boutons and the larger object represent separate entities, the two are sometimes combined in the extracted contour, yielding an undesirable result.

.Still more strikingly is this phenomenon shown by Abbe's diffraction plate (fig.^ If a resolvable grating is considered, the diffraction phenomenon has the appearance shown in fig.

^ Still more strikingly is this phenomenon shown by Abbe's diffraction plate (fig.

^ If this object be viewed by the objective, so that at least the diffraction spectra of 1st order pass the finer divisions, then the corresponding diffraction phenomenon in the back focal plane of the objective has the appearance shown in fig.

26). .This is a so-called cross grating formed by two perpendicular gratings.^ This is a so-called cross grating formed by two perpendicular gratings.

.Through a suitable diaphragm in the back focal plane, banding can easily be produced in the image, which contains neither the vertical nor the horizontal lines of the two gratings, but there exist streaks, whose direction halves the angle under which the two gratings intersect (fig.^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

^ Through a suitable diaphragm in the back focal plane, banding can easily be produced in the image, which contains neither the vertical nor the horizontal lines of the two gratings, but there exist streaks, whose direction halves the angle under which the two gratings intersect (fig.

^ The image produced by a microscope formed of two positive systems (fig.

27). .There can thus be shown structures which are not present in the object.^ There can thus be shown structures which are not present in the object.

.Colonel Dr Woodward of the United States army showed that interference effects appear to produce details in the image which do not exist in the object.^ Colonel Dr Woodward of the United States army showed that interference effects appear to produce details in the image which do not exist in the object.

^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

^ But as the object-side focus F2 lies behind the eyepiece, the real image is not produced, but the converging pencils from the objective are changed by the eyepiece into parallels ; and the point 0 1 in the top of the object y appears at the top to the eye, i.e.

.For example, two to five rows of globules were produced, and photographed, between the bristles of mosquito wings by using oblique illumination.^ For example, two to five rows of globules were produced, and photographed, between the bristles of mosquito wings by using oblique illumination.

In observing with strong systems it is therefore necessary cautiously to distinguish between spectral and real marks. .To determine the utility of an' objective for resolving fine details, one experiments with definite objects, which are usually employed simultaneously for examining its other properties.^ The resolving power can also be determined by using different fine test objects.

^ To determine the utility of an' objective for resolving fine details, one experiments with definite objects, which are usually employed simultaneously for examining its other properties.

^ If microscopic preparations are observed by diffused daylight or by the more or less white light of the usual artificial sources, then an objective of fixed numerical aperture will only represent details of a definite fineness.

.Most important are the fine structures of diatoms such as Surirella gemma and Amphipleura pellucida or artificial fine divisions as in a Nobert's grating.^ Most important are the fine structures of diatoms such as Surirella gemma and Amphipleura pellucida or artificial fine divisions as in a Nobert's grating.

^ Norbert's test plates, which bear graduated groups of extremely fine and narrow divisions are very useful, while the tests of Amphipleura pellucida and Surirella gemma are often employed.

.The examination of the objectives can only be attempted when the different faults of the objective are known.^ The examination of the objectives can only be attempted when the different faults of the objective are known.

^ As was seen when discussing the physical theory, the minute details of the object cause diffractions, and can only be examined if the objective can take up at least two consecutive diffraction spectra.

^ Especially powerful achromatic condensers are really only magnified microscope objectives, with the difference that they are not corrected for the thickness of the cover slip, but for the thickness of the glass on which the object is placed.

.If microscopic preparations are observed by diffused daylight or by the more or less white light of the usual artificial sources, then an objective of fixed numerical aperture will only represent details of a definite fineness.^ If microscopic preparations are observed by diffused daylight or by the more or less white light of the usual artificial sources, then an objective of fixed numerical aperture will only represent details of a definite fineness.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ There is nearly always an arrangement to observe the preparation first in convergent light and then in parallel polarized light.

.All smaller details are not portrayed.^ All smaller details are not portrayed.

.The Fraunhofer formula permits the determination of the most useful magnification of such an objective in order to utilize its full resolving power.^ The Fraunhofer formula permits the determination of the most useful magnification of such an objective in order to utilize its full resolving power.

^ The resolving power can also be determined by using different fine test objects.

^ Finally, this microscopy method remains based on light and therefore is limited by the wavelength used (resolving power ~2000 angstroms, magnification ~2000x).

.As we saw above, the apparent size of a detail of an object must be greater than the angular range of vision, i.e. I'. Therefore we can assume that a detail which appears under an angle of 2' can be surely perceived.^ The greater the visual angle, the more distinctly are the details of the object perceived.

^ As we saw above, the apparent size of a detail of an object must be greater than the angular range of vision, i.e.

^ Therefore we can assume that a detail which appears under an angle of 2' can be surely perceived.

.Supposing, however, there is oblique illumination, then formula (5) can always be applied to determine the magnifying power attainable with at least one objective.^ Supposing, however, there is oblique illumination, then formula (5) can always be applied to determine the magnifying power attainable with at least one objective.

^ For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.

^ To determine the utility of an' objective for resolving fine details, one experiments with definite objects, which are usually employed simultaneously for examining its other properties.

.By substituting y, the size of the object, for d, the smallest value which a single object can have in order to be analysed, and the angle w' by 2', we obtain the magnifying power and the magnification number: V2 = tan w'Id= 2A tan 2'/X; N2 = 2Al tan 2'/A; where 1 equals the sight range of io in.^ By substituting y, the size of the object, for d, the smallest value which a single object can have in order to be analysed, and the angle w' by 2', we obtain the magnifying power and the magnification number: V2 = tan w'Id= 2A tan 2'/X; N2 = 2Al tan 2'/A; where 1 equals the sight range of io in.

^ The resolving power can be as high as a few angstroms and can provide magnifications on the order of 1,000,000x.

^ By using an objective micrometer in place of the object, the magnification of the objective can be ascertained and from this the actual size of the object.

.Even if the details can be recognized with an apparent magnification of 2', the observation may still be inconvenient.^ Even if the details can be recognized with an apparent magnification of 2', the observation may still be inconvenient.

^ But even with such moderate magnification as these instruments permitted many faults were apparent.

^ If the magnification is below the given numbers, the details can either not be seen at all, or only very indistinctly; if, on the contrary, the given magnification is increased, there will still be no more details visible.

This may be improved when the magnification is so increased that the angle under which the object, when still just recognizable, is raised to 4'. The magnification and magnifying number which are most necessary for a microscope with an objective of a given aperture can then be calculated from the formulae: V4 = 2A tan 4'/X; N4 = 2Al tan 4'/A.
.If 0.55 µ is assumed for daylight observation, then according to Abbe (Journ.^ If 0.55 µ is assumed for daylight observation, then according to Abbe ( Journ.

Roy. Soc.,
1882, p. .463) we have the following table for the limits of the magnification numbers, for various microscope objectives, µ = o ooi mm.: A=nsinu.^ By multiplying the magnification of the objective by the number .t .

^ The sine-condition can therefore also be understood as follows: that all objective zones must have the same magnification for the plane-element.

^ When determining the magnification the microscope must be used under exactly the same conditions: neither the length of the tube nor the focal length of the objective may be altered.

d inµ.
0 IO
2.75
53
106
0.30
0.92
1 59
317
0.60
0.46
3 1 7
635
0.90
0.31
47 6
952
i 20
0.23
635
1270
I. 40
0.19
741
1481
1.60
0.17
847
1693
.From this it can be seen that, as a rule, quite slight magnifications suffice to bring all representable details into observation.^ From this it can be seen that, as a rule, quite slight magnifications suffice to bring all representable details into observation.

^ Even if the details can be recognized with an apparent magnification of 2', the observation may still be inconvenient.

^ If the magnification is below the given numbers, the details can either not be seen at all, or only very indistinctly; if, on the contrary, the given magnification is increased, there will still be no more details visible.

.If the magnification is below the given numbers, the details can either not be seen at all, or only very indistinctly; if, on the contrary, the given magnification is increased, there will still be no more details visible.^ There's still nothing more specific than Q1 2010 for Europe, although we're hounding Ubisoft now.
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^ While TEM magnification can be increased substantially to capture more detail, a direct correlation exists between TEM magnification and thermal effects.

^ Unfortunately, there's no detailed plans ...
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.The table shows at the same time the great superiority of the immersion-system over the dry-system with reference to the resolving power.^ The table shows at the same time the great superiority of the immersion-system over the dry-system with reference to the resolving power.

^ In immersion-systems a very much greater aggregate of rays is used in the representation than is possible in dry-systems.

^ The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index.

.With the best immersion-system, having a numerical aperture of 1.6, details of the size o.^ With the best immersion-system, having a numerical aperture of 1.6, details of the size o.

^ The structure of a modern system of this type, with a numerical aperture of I. 30, is shown in fig.

^ He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.

.17 µ can be resolved, while the theoretical maximum of the resolving power is o 167µ, so that the theoretical maximum has almost been reached in practice.^ The lower limit of the resolving power of the eye is reached when the distance is approximately 3438 times the size of the object.

^ Also, since the microscope is based on the use of light, the wavelength of the light used determines the maximum resolving power of the microscope.

^ It is possible to almost double the resolving power, as in the case FIG. 21.

.Still smaller particles cannot be portrayed by using ordinary daylight.^ Still smaller particles cannot be portrayed by using ordinary daylight.

.In order to increase the resolving power, A. Kohler (Zeit.^ In order to increase the resolving power, A. Kohler ( Zeit.

^ The resolving power can be as high as a few angstroms and can provide magnifications on the order of 1,000,000x.

^ As the microscopist usually estimates the resolving power according to the aperture with ordinary day-light, Kohler introduced the " relative resolving power " for ultra-violet light.

f. .Mikros.,
1904, 21, pp.^ Mikros., 1904, 21, pp.

.129, 273) suggested employing ultra-violet light, of a wave-length 275 pp; he thus increased the resolving power to about double that which is reached with day-light, of which the mean wave-length is 550 pp. Light of such short wave-length is, however, not visible, and therefore a photographic plate must be employed.^ Light of such short wave-length is, however, not visible, and therefore a photographic plate must be employed.

^ However, resolving power remains limited.

^ The power of the microscope is thus represented by presupposing day-light with a wave-length of 550 Au.

.Since glass does not transmit the ultra-violet light, quartz is used, but such lenses can only be spherically corrected and not chromatically.^ Since glass does not transmit the ultra-violet light, quartz is used, but such lenses can only be spherically corrected and not chromatically.

^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

^ Correction of the spherical aberration in strong systems with very large aperture can not be brought about by means of a single combination of two lenses, but several partial systems are necessary.

.For this reason the objectives have been called monochromats, as they have only been corrected for light of one wave-length.^ For this reason the objectives have been called monochromats, as they have only been corrected for light of one wave-length.

^ For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

.Further, the different transparencies of the cells for the ultra-violet rays render it unnecessary to dye the preparations.^ Further, the different transparencies of the cells for the ultra-violet rays render it unnecessary to dye the preparations.

^ Improvements in glass lenses, however, have rendered further experiments with precious stones unnecessary.

.Glycerin is chiefly used as immersion fluid.^ Glycerin is chiefly used as immersion fluid.

^ The immersion liquids in common use are water, glycerine, cedar -wood oil, monobromnaphthalene, &c.

M. v. .Rohr's monochromats are constructed with apertures up to 1.25. The smallest resolving detail with oblique lighting is 6 =A/ 2A, where A = 275 µµ. As the microscopist usually estimates the resolving power according to the aperture with ordinary day-light, Kohler introduced the " relative resolving power " for ultra-violet light.^ As the microscopist usually estimates the resolving power according to the aperture with ordinary day-light, Kohler introduced the " relative resolving power " for ultra-violet light.

^ Rohr's monochromats are constructed with apertures up to 1.25.

^ Finally, this microscopy method remains based on light and therefore is limited by the wavelength used (resolving power ~2000 angstroms, magnification ~2000x).

.The power of the microscope is thus represented by presupposing day-light with a wave-length of 550 Au. Then the denominator of the fraction, the numerical aperture, must be correspondingly increased, in order to ascertain the real resolving power.^ In order to increase the resolving power, A. Kohler ( Zeit.

^ The resolving power of an objective depends on its numerical aperture.

^ If the numerical aperture be known the resolving power is easily found.

In this way a monochromat for glycerin of a numerical aperture 1.25 gives a relative numerical aperture of 2.50.
.If the magnification be greater than the resolving power demands, the observation is not only needlessly made more difficult, but the entrance pupil is diminished, and with it a very considerable decrease of clearness, for with an objective of a certain aperture the size of the exit pupil depends upon the magnification.^ The resolving power of an objective depends on its numerical aperture.

^ THE Testing Of The Microscope The excellence of a microscope objective depends on its definition and its resolving power.

^ The dependence of the clearness of the image on the aperture of the system, i.e.

The diameter of FIG. 20.
0 st FIG. 27.
N2.
the exit pupil of the microscope is about 0.04 in. with the magnification N2, and about 0.02 in. with the magnification .N4. Moreover, with such exceptionally narrow pencils shadows are formed on the retina of the observer's eye, from the irregularities in the eye itself.^ Moreover, with such exceptionally narrow pencils shadows are formed on the retina of the observer's eye, from the irregularities in the eye itself.

^ Both lenses together form the exit-pupil of the objective behind the eyelens, so that this image, the exit-pupil of the total system or the Ramsden circle, is accessible to the eye of the observer.

.These disturbances are called " entoptical phenomena."^ These disturbances are called " entoptical phenomena."

From the section Regulation of the Rays (above) it is seen that the resolving power is opposed to the depth of definition, which is measured by the reciprocal of the numerical aperture, I/A.

Dark-field Illumination

.It is sometimes desirable to make minutest objects in a preparation specially visible.^ It is sometimes desirable to make minutest objects in a preparation specially visible.

.This can be done by cutting off the chief maximum and using only the diffracted spectra for producing the image.^ This can be done by cutting off the chief maximum and using only the diffracted spectra for producing the image.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

.At least two successive diffraction maxima must be admitted through the objective for there to be any image of the objects.^ At least two successive diffraction maxima must be admitted through the objective for there to be any image of the objects.

^ If a grating is placed as object before the microscope objective, Abbe showed that in the image there is intermittent clear and dark banding only, if at least two consecutive diffraction spectra enter into the objective and contribute towards the image.

^ All details of the object so resolved are perceived, if two diffraction maxima can be passed through the objective, so that the character of the object is seen in the image, even if an exact resemblance has not yet been attained.

.With this device these particles appear bright against a dark background, and can be easily seen.^ With this device these particles appear bright against a dark background, and can be easily seen.

^ These diffracting details become especially distinct if the direct lighting cone of rays, the spectrum of zero:order or the chief maximum, is not allowed to enter the objective and instead only two or more diffraction maxima are taken up; the details then appear bright on a dark background.

.The cutting off of the chief maximum can be effected by a suitable diaphragm in the back focal plane of the objective.^ If a diaphragm lying in the back focal plane of the objective forms the exit pupil for the objective, as in figs.

^ The cutting off of the chief maximum can be effected by a suitable diaphragm in the back focal plane of the objective.

^ If one cuts out by a diaphragm in the back focal plane of the objective all diffraction spectra except the principal maximum, one sees in the image a field divided into two halves, which show with different clearness, but no banding.

.But, owing to the various partial reflections which the illuminating cone of rays undergoes when traversing the surfaces of the lenses, a portion of the light comes again into the preparation, and into the eye of the observer, thus veiling the image.^ But, owing to the various partial reflections which the illuminating cone of rays undergoes when traversing the surfaces of the lenses, a portion of the light comes again into the preparation, and into the eye of the observer, thus veiling the image.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

^ For examining preparations in polarized light a polarizer D is introduced n the illuminating apparatus below the diaphragm and an analyser E ai .

.This defect can be avoided (after Abbe) if a small central portion of the back surface of the front lens be ground away and blackened; this portion should exactly catch the direct cone of rays, whilst the edges of the lens let the deflected cone of rays pass through (fig.^ C and D are the outermost rays which can pass through the instrument.

^ This defect can be avoided (after Abbe) if a small central portion of the back surface of the front lens be ground away and blackened; this portion should exactly catch the direct cone of rays, whilst the edges of the lens let the deflected cone of rays pass through (fig.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

28).
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rapqamnoIWARU (By permission of C. Zeiss.) FIG. 28.
.The large loss of light, which is caused in dark-field illumination by the cutting off of the direct cone of rays, must be compensated by employing exceptionally strong sources.^ How is it different from dark-field illumination?
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^ The large loss of light, which is caused in dark-field illumination by the cutting off of the direct cone of rays, must be compensated by employing exceptionally strong sources.

^ Dark-field Illumination .

.By dark-field illumination it is even possible to make such small details of objects perceptible as are below the limits of the resolving power.^ How is it different from dark-field illumination?
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^ However, resolving power remains limited.

^ Finally, this microscopy method remains based on light and therefore is limited by the wavelength used (resolving power ~2000 angstroms, magnification ~2000x).

.It is a similar phenomenon to that which arises when a ray of sunlight falls into a darkened room.^ It is a similar phenomenon to that which arises when a ray of sunlight falls into a darkened room.

.The extremely small particles of dust (motes in a sunbeam) in the rays are made perceptible by the diffracted light, whilst by ordinary illumination they are invisible.^ The extremely small particles of dust (motes in a sunbeam) in the rays are made perceptible by the diffracted light, whilst by ordinary illumination they are invisible.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

^ The limit at which sub-microscopic particles are made visible is dependent upon the specific intensity of the source of light.

.The same observation can be made with the cone of rays of a reflector, and in the same way the fine rain-drops upon a dark background and the fixed stars in the sky become visible.^ The same observation can be made with the cone of rays of a reflector, and in the same way the fine rain -drops upon a dark background and the fixed stars in the sky become visible.

^ The half cones of rays have now semicircular sections, the diaphragms having the same form.

^ The demands made upon the eyepiece, which has to represent a relatively large field by narrow cones of rays, are not very considerable.

.It is not possible to recognize the exact form of the minute objects because their apparent size is much too small; only their presence is observable.^ It is not possible to recognize the exact form of the minute objects because their apparent size is much too small; only their presence is observable.

^ In addition, the particles can only be recognized as separate objects if their apparent distance from one another is greater than the angular definition of sight.

^ As we saw above, the apparent size of a detail of an object must be greater than the angular range of vision, i.e.

.In addition, the particles can only be recognized as separate objects if their apparent distance from one another is greater than the angular definition of sight.^ In addition, the particles can only be recognized as separate objects if their apparent distance from one another is greater than the angular definition of sight.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

Ultramicroscopy

.This method of illumination has been used by H. Siedentopf in his ultramicroscope.^ This method of illumination has been used by H. Siedentopf in his ultramicroscope.

.The image consists of a diffraction disk from whose form and size certain conclusions may be drawn as to the size and form of the object.^ The image consists of a diffraction disk from whose form and size certain conclusions may be drawn as to the size and form of the object.

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

^ The angle under which the object appears depends upon the distance and size of the object, or, in other words, the size of the image on the retina is determined by the distance and the dimensions of the object.

.It is impossible to get a representation as from an object.^ It is impossible to get a representation as from an object.

.Very finely divided sub-microscopic particles in liquids or in transparent solids can be examined; and the method has proved exceptionally valuable in the investigation of colloidal solutions.^ Very finely divided sub-microscopic particles in liquids or in transparent solids can be examined; and the method has proved exceptionally valuable in the investigation of colloidal solutions.

^ A related method involves examining the edge strength and region intensity values within the area close to the edge between the regions.

^ No method for programmatically querying or setting other microscope parameters (such as magnification, focus value, illumination, etc.

.Siedentopf employed two illuminating arrangements.^ Siedentopf employed two illuminating arrangements.

.With the .orthogonal arrangement for illuminating and observing the beam of light traverses an extremely fine slit through a well-corrected system, whose optic axis is perpendicular to the axis of the microscope; the system reduces the dimensions of the beam to about 2 to 4 in the focal plane of the objective.^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

^ Suppose that a well corrected objective is employed.

^ With the .orthogonal arrangement for illuminating and observing the beam of light traverses an extremely fine slit through a well-corrected system, whose optic axis is perpendicular to the axis of the microscope; the system reduces the dimensions of the beam to about 2 to 4 in the focal plane of the objective.

.For the microscopic observation it is the same as if a thin section of a thickness of 2 to 4 had been shown.^ For the microscopic observation it is the same as if a thin section of a thickness of 2 to 4 had been shown.

^ In addition, variations in section thickness may necessitate a change in microscope focus.

^ After the thin section of tissue is prepared and placed in the TEM, the microscope is focused and the desired magnification is selected through normal procedures.

.In this optical way it is possible to show thin sections even in liquid preparations.^ In this optical way it is possible to show thin sections even in liquid preparations.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

^ After the thin section of tissue is prepared and placed in the TEM, the microscope is focused and the desired magnification is selected through normal procedures.

.The inconvenience of orthogonal illumination, which certainly gives better results, is avoided in the coaxial apparatus.^ The inconvenience of orthogonal illumination, which certainly gives better results, is avoided in the coaxial apparatus.

.Care must here be taken, by using suitable dark-field screens, that no direct rays enter the observing system.^ Care must here be taken, by using suitable dark-field screens, that no direct rays enter the observing system.

^ In dark field illumination care has to be taken that no direct rays reach the objective, and hence a good dark field illumination can be produced if the condenser system has a larger aperture than the objective.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

The only sources of light are sunlight or the electric arc. .The limit at which sub-microscopic particles are made visible is dependent upon the specific intensity of the source of light.^ The limit at which sub-microscopic particles are made visible is dependent upon the specific intensity of the source of light.

^ With sunlight particles can be made visible to a size of about o o04 ,u.

^ He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.

.With sunlight particles can be made visible to a size of about o o04 ,u.^ With sunlight particles can be made visible to a size of about o o04 ,u.

^ Apparatus for a good dark field illumination has received much attention, because in this way ultra-microscopical particles can be made visible.

^ The limit at which sub-microscopic particles are made visible is dependent upon the specific intensity of the source of light.

Production of the Image

.As shown in Lens and Aberration, for reproduction through a single lens with spherical surfaces, a combination of the rays is only possible for an extremely small angular aperture.^ As shown in Lens and Aberration , for reproduction through a single lens with spherical surfaces, a combination of the rays is only possible for an extremely small angular aperture.

^ Even if the object-point on the axis cannot be reproduced quite free from aberration through such a lens, because aberrations of the type of an under-correction have been produced by the first plane outer limiting surface, yet the defects with the strong refraction are relatively small and can be well compensated by other systems.

^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

The aberrations, both spherical and chromatic, increase very rapidly with the aperture. .If it were not possible to recombine in one image-point the rays leaving the objective and derived from one object-point, i.e. to eliminate the spherical and chromatic aberrations, the large angular aperture of the objective, which is necessary for its resolving power, would be valueless.^ The resolving power of an objective depends on its numerical aperture.

^ The aberrations, both spherical and chromatic, increase very rapidly with the aperture.

^ If it were not possible to recombine in one image-point the rays leaving the objective and derived from one object-point, i.e.

.Owing to these aberrations, the fine structure, which in consequence of the large aperture could be resolved, could not be perceived.^ Owing to these aberrations, the fine structure, which in consequence of the large aperture could be resolved, could not be perceived.

^ Correction of the spherical aberration in strong systems with very large aperture can not be brought about by means of a single combination of two lenses, but several partial systems are necessary.

^ This refers to systems with small apertures, but still more so to systems with large ones; chromatic aberrations are exceptionally increased by large apertures.

.In other words, a sufficiently good and distinct image as the resolving power permits cannot be arrived at, until the elimination, or a sufficient diminution, of the spherical and chromatic aberrations has been brought about.^ In other words, we define a function as to how "good" the registration is between two sections, then we loop through each of the sections and minimize this function.

The objective and eyepiece have. such different functions that as a rule it is not possible to correct the aberrations of one system by those of the other. .Such a compensation is only possible for one single defect, as we shall see later.^ Such a compensation is only possible for one single defect, as we shall see later.

^ Although such systems have been made recently for special purposes, this construction was abandoned, and a more complex one adopted, which also made the production of better objectives possible; this is the principle of the compensation of the aberrations produced in the different parts of the objective.

^ D is used for a condenser, which has a blackened section on the back of the front lens of such a size that no light can enter the objective A. In this way it is only possible for diffracted rays to enter the objective.

.The demands made upon the eyepiece, which has to represent a relatively large field by narrow cones of rays, are not very considerable.^ The demands made upon the eyepiece, which has to represent a relatively large field by narrow cones of rays, are not very considerable.

^ Even in powerful magnifications a good image exists in all parts of a relatively large field, and the free working distance is fairly large.

^ Its purpose in a microscope is by means of narrow cones of rays to represent at infinity the real magnified image which the objective produces.

.It is therefore not very difficult to produce a usable eyepiece.^ It is therefore not very difficult to produce a usable eyepiece.

^ Since one is therefore forced to use a very small region as the target, it is difficult to produce a good match and its utility is severely restricted.

^ Typically these regions are very small and therefore produce a large number of undesired "noise regions".

.On the other hand, the correction of the objective presents many difficulties.^ Method The automated image acquisition method presented here addresses many of the difficulties listed above.

.We will now examine the conditions which must be fulfilled by an objective, and then how far these conditions have been realized.^ We will now examine the conditions which must be fulfilled by an objective, and then how far these conditions have been realized.

^ The sine-condition is, however, the most important as far as the microscopic representation is concerned, because it must be possible to represent a surfaceelement through the objective by wide cones of rays.

^ Since in these systems the sine-condition can be fulfilled for several colours, the quality of the images of points beyond the axis is better.

.Consider the aberrations which may arise from the representation by a system of wide aperture with monochromatic light, i.e. the spherical aberrations.^ P224140 systems of wide aperture.

^ Consider the aberrations which may arise from the representation by a system of wide aperture with monochromatic light, i.e.

^ He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.

.The rays emitted from an axial object-point are not combined into one image-point by an ordinary biconvex lens of fixed aperture, but the central rays come to a more distant focus than the outer rays.^ A potentially more serious problem is the lack of fiduciary points, since the contours of cells change from one section to another and boundaries may shift.

^ Rounded topped rods are more vulnerable to a sudden electric spark than are the pointed rods.
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^ While the traditional case of simple bifurcation is one contour splitting uniformly into two, a number of other cases pose difficulties: Clearly, we can not assume that simply because we have one contour on one section and more than one on the next that we may simply assume the object has branched.

.The so-called " caustic " occupies a definite position in the image-space.^ The so-called " caustic " occupies a definite position in the image-space.

.The spherical aberrations, however, can be overcome, or at least so diminished that they are quite harmless, by forming appropriate combinations of lenses.^ The spherical aberrations, however, can be overcome, or at least so diminished that they are quite harmless, by forming appropriate combinations of lenses.

^ As shown in Lens and Aberration , for reproduction through a single lens with spherical surfaces, a combination of the rays is only possible for an extremely small angular aperture.

^ A second method for diminishing the spherical aberration was to alter the distances of the single systems, a method still used.

.The aberration of rays in which the outer rays intersect the axis at a shorter distance than the central rays is known as " undercorrection."^ The aberration of rays in which the outer rays intersect the axis at a shorter distance than the central rays is known as " undercorrection."

^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

.The reverse is known as " over-correction."^ The reverse is known as " over-correction."

.By selecting the radii of the surfaces and the kind of glass the underor over-correction can be regulated.^ By selecting the radii of the surfaces and the kind of glass the underor over-correction can be regulated.

.Thus it is possible to correct a system by combining a convex and a concave lens, if both have aberrations of the same amount but of opposite signs.^ Thus it is possible to correct a system by combining a convex and a concave lens, if both have aberrations of the same amount but of opposite signs.

^ Correction of the spherical aberration in strong systems with very large aperture can not be brought about by means of a single combination of two lenses, but several partial systems are necessary.

^ He used chiefly a highly curved piano-convex front lens, which has since always been employed in strong systems.

.In this case the power of the crown lens must preponderate so that the resulting lens is of the same sign, but of a little less power.^ In this case the power of the crown lens must preponderate so that the resulting lens is of the same sign, but of a little less power.

^ Thus it is possible to correct a system by combining a convex and a concave lens, if both have aberrations of the same amount but of opposite signs.

.Correction of the spherical aberration in strong systems with very large aperture can not be brought about by means of a single combination of two lenses, but several partial systems are necessary.^ Correction of the spherical aberration in strong systems with very large aperture can not be brought about by means of a single combination of two lenses, but several partial systems are necessary.

^ The aberrations, both spherical and chromatic, increase very rapidly with the aperture.

^ As both eyepieces are used with very small apertures (about f : 20) no attempt has been made to overcome the spherical aberrations, which are usually very slight; neither, as a rule, are the eyepieces chromatically corrected, care has only to be taken by a suitable choice of the distance of one lens from the other, that the coloured images derived from a colourless object should have the same apparent size.

.Further, undercorrected systems must be combined with over-corrected ones.^ Further, undercorrected systems must be combined with over-corrected ones.

^ This effect can be corrected as well, but the low dynamic range of the system further hampers corrective efforts.

^ Future Directions While the issues raised provide an intuitive argument for correct results, one is left with a feeling that a more precise method of quantification must be possible.

.Another way of correcting this system is to alter the distances.^ Another way of correcting this system is to alter the distances.

^ A second method for diminishing the spherical aberration was to alter the distances of the single systems, a method still used.

^ The optical system must be kept at a certain distance and well centred, and a correct position for the object in relation to the system must be assured.

.If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

^ These brass forms can be removed and replaced only in the positions shown, but after having been inserted in the above positions (with the contacts pointing outwardly) they can be rotated freely.
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^ Since in these systems the sine-condition can be fulfilled for several colours, the quality of the images of points beyond the axis is better.

.The representation, free from aberration, of a small surface-element, is only possible, as Abbe has shown, if the objective simultaneously fulfils the " sine-condition," i.e. if the ratio of the sine of the aperture u on the object-side to the sine of the corresponding aperture u' on the image-side is constant, i.e. if n sin u/sin u' = C, in which C is a constant.^ If the sine-condition is not fulfilled but the spherical aberrations in the axis have been removed, then the image shown in fig.

^ The representation, free from aberration, of a small surface-element, is only possible, as Abbe has shown, if the objective simultaneously fulfils the " sine-condition," i.e.

^ F 1 ' =objectand image-side foci of objective.

.The sine-condition is in contrast to the tangent-condition, which must be regarded as the point-by-point representation of the whole object-space in the image-space (see Lens), and according therefore the equation n tan u/tan u' = C must exist.^ The sine-condition is in contrast to the tangent-condition, which must be regarded as the point-by-point representation of the whole object-space in the image-space (see Lens ), and according therefore the equation n tan u/tan u' = C must exist.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ This representation acquires a special importance if the object be micrometrically measured, for an inaccuracy in focusing does not involve an alteration of the size of the image.

.These two conditions are only compatible when the representation is made with quite narrow pencils, and where the apertures are so small that the sines and tangents are of about the same value.^ Google boasts that these are only two of 1,500 new features, and that Chrome 4 runs 40% faster than Chrome 3.
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.Very large apertures occur in strong microscope objectives, and hence the two conditions are not compatible.^ Very large apertures occur in strong microscope objectives, and hence the two conditions are not compatible.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ In dark field illumination care has to be taken that no direct rays reach the objective, and hence a good dark field illumination can be produced if the condenser system has a larger aperture than the objective.

.The sine-condition is, however, the most important as far as the microscopic representation is concerned, because it must be possible to represent a surfaceelement through the objective by wide cones of rays.^ The sine-condition is, however, the most important as far as the microscopic representation is concerned, because it must be possible to represent a surfaceelement through the objective by wide cones of rays.

^ Entocentric transmission through a microscope objective.

^ For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.

.The removal of the spherical aberration and the sine-condition can be accomplished only for two conjugate points.^ The removal of the spherical aberration and the sine-condition can be accomplished only for two conjugate points.

^ If the sine-condition is not fulfilled but the spherical aberrations in the axis have been removed, then the image shown in fig.

^ These brass forms can be removed and replaced only in the positions shown, but after having been inserted in the above positions (with the contacts pointing outwardly) they can be rotated freely.
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.A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.^ Suppose that a well corrected objective is employed.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ If microscopic preparations are observed by diffused daylight or by the more or less white light of the usual artificial sources, then an objective of fixed numerical aperture will only represent details of a definite fineness.

.As soon as the object is moved a short distance away from this spot the representation is quite useless.^ As soon as the object is moved a short distance away from this spot the representation is quite useless.

^ In entocentric transmission this phenomenon appears in general as in the case of the contemplation of perspective representations at a too short distance, the objects appearing flattened.

^ The distance of the centres of the semicircular entrance pupils and their distance from the object regulates the difference of the two perspective representations, which are presented one to the right eye and one to the left.

.Hence the importance of observing the length of the tube in strong systems.^ Hence the importance of observing the length of the tube in strong systems.

^ Strong systems produce in the proximity of their back focal plane an image of the scale, which can be inspected with a weak auxiliary microscope, and the length of the visible part of the graduation determined.

^ In observing with strong systems it is therefore necessary cautiously to distinguish between spectral and real marks.

.If the sine-condition is not fulfilled but the spherical aberrations in the axis have been removed, then the image shown in fig.^ The removal of the spherical aberration and the sine-condition can be accomplished only for two conjugate points.

^ If the sine-condition is not fulfilled but the spherical aberrations in the axis have been removed, then the image shown in fig.

^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

19 results. The cones of rays issuing from a point situated only a little to the FIG. 29. - The lens is spherically corrected for 00', but the sinecondition is not fulfilled. .Hence the different magnifications of a point 0 1 beyond the axis.^ Hence the different magnifications of a point 0 1 beyond the axis.

^ Since in these systems the sine-condition can be fulfilled for several colours, the quality of the images of points beyond the axis is better.

^ As with the simple microscope, different observers see differently in the same compound microscope; and hence the magnification varies with the power of accommodation.

side, which .traverse different zones of the objective, have a different magnification.^ The sine-condition can therefore also be understood as follows: that all objective zones must have the same magnification for the plane-element.

^ Since, however, the difference of chromatic magnification cannot be overcome in powerful objectives, this error is still further increased by the eyepiece.

^ As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.

.The sine-condition can therefore also be understood as follows: that all objective zones must have the same magnification for the plane-element.^ The sine-condition can therefore also be understood as follows: that all objective zones must have the same magnification for the plane-element.

^ The sine-condition is, however, the most important as far as the microscopic representation is concerned, because it must be possible to represent a surfaceelement through the objective by wide cones of rays.

^ We will now examine the conditions which must be fulfilled by an objective, and then how far these conditions have been realized.

.According to Abbe, a system can only be regarded as aplanatic if it is spherically corrected for not only one axial point, but when it also fulfils the sine-condition and thus magnifies equally in all zones a surface-element situated vertically on the axis at this point.^ The removal of the spherical aberration and the sine-condition can be accomplished only for two conjugate points.

^ According to Abbe, a system can only be regarded as aplanatic if it is spherically corrected for not only one axial point, but when it also fulfils the sine-condition and thus magnifies equally in all zones a surface-element situated vertically on the axis at this point.

^ If the sine-condition is not fulfilled but the spherical aberrations in the axis have been removed, then the image shown in fig.

.A second method of correcting the spherical aberration depends FIG. 30.-0' is the virtual image on the notion of aplanatic points.^ A second method of correcting the spherical aberration depends FIG. 30.-0' is the virtual image on the notion of aplanatic points.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

of 0 formed at a spherical surIf there are two transparent face of centre C and radius CS. substances separated from one another by a spherical surface, then there are two points on the axis where they can be reproduced free from error by monochromatic light, and these are called " aplanatic points." The first is the centre of the sphere. .All rays issuing from this point pass unrefracted through the dividing surface; its image-point coincides with it.^ C and D are the outermost rays which can pass through the instrument.

^ All rays issuing from this point pass unrefracted through the dividing surface; its image-point coincides with it.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

.Besides this there is a second point on the axis, from which all issuing rays are so refracted at the surface of the sphere that, after the refraction, they appear to originate from one point - the image-point (see fig.^ They may not be the original ones.
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^ Besides this there is a second point on the axis, from which all issuing rays are so refracted at the surface of the sphere that, after the refraction, they appear to originate from one point - the image-point (see fig.

^ All rays issuing from this point pass unrefracted through the dividing surface; its image-point coincides with it.

30). .With this, the objectpoint 0, and consequently the image-point 0' also, will be at a quite definite distance from the centre.^ With this, the objectpoint 0, and consequently the image-point 0' also, will be at a quite definite distance from the centre.

^ The principal rays, which on the object-side connect the object-points with the centre of the entrance pupil, intersect the axis on the image-side at the centre of rotation M of the eye.

^ In consequence of these residual aberrations, every object-point is not reproduced in an ideal image-point, but as a small circle of aberration.

.If however the object-point does not lie in the medium with the index n, but before it, and the medium is, for example, like a front lens, still limited by a plane surface, just in front of which is the object-point, then in traversing the plane surface spherical aberrations of the under-corrected type again arise, and must be removed.^ If however the object-point does not lie in the medium with the index n, but before it, and the medium is, for example, like a front lens, still limited by a plane surface, just in front of which is the object-point, then in traversing the plane surface spherical aberrations of the under-corrected type again arise, and must be removed.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ Even if the object-point on the axis cannot be reproduced quite free from aberration through such a lens, because aberrations of the type of an under-correction have been produced by the first plane outer limiting surface, yet the defects with the strong refraction are relatively small and can be well compensated by other systems.

.By homogeneous immersion the object-point can readily be reduced to an aplanatic point.^ By homogeneous immersion the object-point can readily be reduced to an aplanatic point.

.By experiment Abbe proved that old, good microscope objectives, which by mere testing had become so corrected that they produced usable images, were not only free from spherical aberrations, but also fulfilled the sine-condition, and were therefore really aplanatic systems.^ The image produced by a microscope formed of two positive systems (fig.

^ The removal of the spherical aberration and the sine-condition can be accomplished only for two conjugate points.

^ In the commonest compound microscopes, which consist of two positive systems, a real magnified image is produced by the objective.

.The second aberration which must be removed from microscope objectives are the chromatic.^ The second aberration which must be removed from microscope objectives are the chromatic.

^ To obtain the magnification of the complete microscope we must combine the objective magnification M with the action of the eyepiece.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

.To diminish these a collective lens of crown-glass is combined with a dispersing lens of flint; in such a system the red and the blue rays intersect at a point (see Aberration).^ To diminish these a collective lens of crown-glass is combined with a dispersing lens of flint; in such a system the red and the blue rays intersect at a point (see Aberration ).

^ The system is under-corrected for red, and over-corrected for blue rays.

^ The transverse sections of these cones of rays diverge more or less from the transverse section of the chosen blue and red cones, and produce a secondary spectrum in the image, and the images still appear to have a slightly coloured edge, mostly greenish-yellow or purple ; in other words, a chromatic difference of the spherical aberrations arises (see fig.

.In systems employed for visual observation (to which class the microscope belongs) the red and blue rays, which include the physiologically most active part of the spectrum, are combined; but rays other than the two selected are not united in one point.^ The system is under-corrected for red, and over-corrected for blue rays.

^ In systems employed for visual observation (to which class the microscope belongs) the red and blue rays, which include the physiologically most active part of the spectrum, are combined; but rays other than the two selected are not united in one point.

^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

.The transverse sections of these cones of rays diverge more or less from the transverse section of the chosen blue and red cones, and produce a secondary spectrum in the image, and the images still appear to have a slightly coloured edge, mostly greenish-yellow or purple; in other words, a chromatic difference of the spherical aberrations arises (see fig.^ The transverse sections of these cones of rays diverge more or less from the transverse section of the chosen blue and red cones, and produce a secondary spectrum in the image, and the images still appear to have a slightly coloured edge, mostly greenish-yellow or purple ; in other words, a chromatic difference of the spherical aberrations arises (see fig.

^ In the apochromats the chromatic difference of the spherical aberrations is eliminated, for the spherical aberration is completely avoided for three colours.

^ Showing a system with chromatic difference of spherical aberration.

31). .This refers to systems with small apertures, but still more so to systems with large ones; chromatic aberrations are exceptionally increased by large apertures.^ The aberrations, both spherical and chromatic, increase very rapidly with the aperture.

^ This refers to systems with small apertures, but still more so to systems with large ones; chromatic aberrations are exceptionally increased by large apertures.

^ Although such systems have been made recently for special purposes, this construction was abandoned, and a more complex one adopted, which also made the production of better objectives possible; this is the principle of the compensation of the aberrations produced in the different parts of the objective.

.The new glasses produced at Schott's glass works, Jena, possessed in part optical qualities which differed considerably from those of the older kinds of glass.^ The new glasses produced at Schott's glass works, Jena , possessed in part optical qualities which differed considerably from those of the older kinds of glass.

^ Schott succeeded, however, in producing glasses which with a comparatively low refraction have a high dispersion, and with a high refraction a low dispersion.

.In the old crown and flint glass a high FIG. 3 i.^ In the old crown and flint glass a high FIG. 3 i.

^ Amici chiefly employed cemented pairs of lenses consisting of a plano-convex flint lens and a biconvex crown lens(fig.

^ To diminish these a collective lens of crown-glass is combined with a dispersing lens of flint; in such a system the red and the blue rays intersect at a point (see Aberration ).

- .Showing a system with chromatic difference of spherical aberration.^ Showing a system with chromatic difference of spherical aberration.

^ The aberrations, both spherical and chromatic, increase very rapidly with the aperture.

^ With this mineral also spherical and chromatic aberration are a fraction of that of a glass lens, but double refraction, which involves a doubling of the image, is fatal to its use.

0" = image of 0 for red light; O"' for blue. .The system is under-corrected for red, and over-corrected for blue rays.^ The system is under-corrected for red, and over-corrected for blue rays.

^ To diminish these a collective lens of crown-glass is combined with a dispersing lens of flint; in such a system the red and the blue rays intersect at a point (see Aberration ).

^ In most cases, and also in corrected systems, the intersection of the principal rays is no longer available for the centre of rotation of the eye, and this kind of observation is impossible.

refractive index was always connected with a strong dispersion and the reverse. .Schott succeeded, however, in producing glasses which with a comparatively low refraction have a high dispersion, and with a high refraction a low dispersion.^ Schott succeeded, however, in producing glasses which with a comparatively low refraction have a high dispersion, and with a high refraction a low dispersion.

^ The new glasses produced at Schott's glass works, Jena , possessed in part optical qualities which differed considerably from those of the older kinds of glass.

^ To reduce the aberrations Sir David Brewster proposed to employ in the place of glass transparent minerals of high refractive index and low dispersion .

.By using these glasses and employing minerals with special optical properties, it is possible to correct objectives so that three colours can be combined, leaving only a quite slight tertiary spectrum, and removing the spherical aberration for two colours.^ It would have been more correct to have employed these objectives in a reverse position.

^ Suppose that a well corrected objective is employed.

^ The removal of the spherical aberration and the sine-condition can be accomplished only for two conjugate points.

.Abbe called such systems " apochromats."^ Abbe called such systems " apochromats."

^ The most perfect microscope objective was invented by E. Abbe in 1886 in the so-called apochromatic objective.

^ Good apochromats often have as many as twelve lenses, whilst systems of simpler construction are only achromatic, and are therefore called " achromats."

.Good apochromats often have as many as twelve lenses, whilst systems of simpler construction are only achromatic, and are therefore called " achromats."^ Good apochromats often have as many as twelve lenses, whilst systems of simpler construction are only achromatic, and are therefore called " achromats."

^ Such systems with a so-called homogeneous immersion were first constructed after the plan of E. Abbe in 1878 in the Zeiss workshops at the instigation of J. W. Stephenson.

^ The weak compensation oculars resemble a Huygenian eyepiece with achromatic eye-lens, whilst the more powerful ones are of a different construction.

.Even in apochromats it is not possible to entirely remove the chromatic difference of magnification, i.e. the images produced by the red rays are somewhat smaller than the images produced by the blue.^ Even in apochromats it is not possible to entirely remove the chromatic difference of magnification, i.e.

^ The transverse sections of these cones of rays diverge more or less from the transverse section of the chosen blue and red cones, and produce a secondary spectrum in the image, and the images still appear to have a slightly coloured edge, mostly greenish-yellow or purple ; in other words, a chromatic difference of the spherical aberrations arises (see fig.

^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

.A white object is represented with blue streaks and a black one with red streaks.^ A white object is represented with blue streaks and a black one with red streaks.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

.This aberration can, however, be successfully controlled by a suitable eyepiece (see below).^ This aberration can, however, be successfully controlled by a suitable eyepiece (see below).

.A further aberration which can only be overcome with difficulty, and even then only partially, is the " curvature of the field, " i.e. the points situated in the middle and at the edge of the plane object can not be seen clearly at the same focusing.^ A further aberration which can only be overcome with difficulty, and even then only partially, is the " curvature of the field, " i.e.

^ Only points lying on the plane focused for can be sharply reproduced in the retina, which acts as object-plane to the retina.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

Historical Development

.The first real improvement in the microscope objective dates from 1830 when V. and C. Chevalier, at first after the designs of Selligue, produced objectives, consisting of several achromatic systems arranged one above the other.^ It consistes of a balance, from one arm of which is suspended a brass weight, and from the other a large hollow sphere....
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The systems could be used separately or in any combination. .A second method for diminishing the spherical aberration was to alter the distances of the single systems, a method still used.^ Method 6.2.1 Interactive method An initial approach to the mosaicking problem was to create an interactive system in C++ with the ImageVision library for use on SGI graphics workstations.

^ The rationale for using this method was to determine if it was possible to have the system "learn" the areas of likely maximum cross-correlation and verify the existence of a pattern.

^ The figure of this microscope as altered by Mr. Jones shows that it is still not as useful as the "most" improved model, which must, of course, have been a still later model.
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.Selligue had no particular comprehension of the problem, for his achromatic single systems were simply telescope objectives corrected for an infinitely distant point, and were placed so that the same surface was turned towards the object in the microscope objective as in the telescope objective; although contrary to the telescope, the distance of the object in the microscope objective is small in proportion to the distance of the image.^ Toward this end, traditional image processing methods are found to be ineffective and a novel Closed Object Operator is described.

^ The first issue to be addressed is whether the points detected truly represent the surface of the objects that exist in the tissue.

^ As described briefly above, we use image processing and, when necessary, manual intervention to derive points that lie on the surface of the objects of interest.

.It would have been more correct to have employed these objectives in a reverse position.^ The points of these corrected contours are used to generate a triangle mesh that can be visualized or modeled by employing traditional computer graphics techniques.

FIG. 32.
FIG. 33.
.These circumstances were considered by Chevalier and Lister.^ These circumstances were considered by Chevalier and Lister.

.Lister showed that a combination of lenses can be achromatic for only two points on the axis, and therefore that the single systems must be so arranged that the aplanatic (virtual) image-point 0' (fig.^ Many such video electron micrographs must be reassembled to reproduce a single image of the entire section.

^ The Laplacian kernel is particularly tuned for detecting points (either 4-connected or 8-connected) and is therefore highly susceptible to point-based camera noise in the image.

^ Therefore, we must first find the point of attraction pa on the contour below for each point p on the contour above, then add the distances between each pair of points.

.32) of the first system coincides with the object-point of the next system.^ The first issue to be addressed is whether the points detected truly represent the surface of the objects that exist in the tissue.

^ In addition it will be supposed that the centre of the pupil of the observer coincides with the back focal point of the system.

.This system will always be aplanatic.^ This system will always be aplanatic.

.These objectives permitted a much larger aperture than a simple achromatic system.^ These objectives permitted a much larger aperture than a simple achromatic system.

^ As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.

^ In dark field illumination care has to be taken that no direct rays reach the objective, and hence a good dark field illumination can be produced if the condenser system has a larger aperture than the objective.

.Although such systems have been made recently for special purposes, this construction was abandoned, and a more complex one adopted, which also made the production of better objectives possible; this is the principle of the compensation of the aberrations produced in the different parts of the objective.^ Although such systems have been made recently for special purposes, this construction was abandoned, and a more complex one adopted, which also made the production of better objectives possible; this is the principle of the compensation of the aberrations produced in the different parts of the objective.

^ Antony van Leeuwenhoek appears to be the first to succeed in grinding and polishing lenses of such short focus and perfect figure as to render the simple microscope a better instrument for most purposes than any compound microscope then constructed.

^ Even if the object-point on the axis cannot be reproduced quite free from aberration through such a lens, because aberrations of the type of an under-correction have been produced by the first plane outer limiting surface, yet the defects with the strong refraction are relatively small and can be well compensated by other systems.

.Even Lister, who proceeded on quite different lines, hinted at the possibility of such a compensation.^ Even Lister, who proceeded on quite different lines, hinted at the possibility of such a compensation.

^ Although such systems have been made recently for special purposes, this construction was abandoned, and a more complex one adopted, which also made the production of better objectives possible; this is the principle of the compensation of the aberrations produced in the different parts of the objective.

^ By dark-field illumination it is even possible to make such small details of objects perceptible as are below the limits of the resolving power.

.This method makes it specially possible to overcome the chromatic and spherical aberrations of higher orders and to fulfil - the sine-condition, and the chief merit of this improvement belongs to Amici.^ This method makes it specially possible to overcome the chromatic and spherical aberrations of higher orders and to fulfil - the sine-condition, and the chief merit of this improvement belongs to Amici.

^ If the sine-condition is not fulfilled but the spherical aberrations in the axis have been removed, then the image shown in fig.

^ If, by these methods, a point in the optic axis has been freed from aberration, it does not follow that a point situated only a very small distance from the optic axis can also be represented without spherical aberration.

.He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.^ P224140 systems of wide aperture.

^ He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.

^ The dependence of the clearness of the image on the aperture of the system, i.e.

.He used chiefly a highly curved piano-convex front lens, which has since always been employed in strong systems.^ He used chiefly a highly curved piano-convex front lens, which has since always been employed in strong systems.

^ Amici chiefly employed cemented pairs of lenses consisting of a plano-convex flint lens and a biconvex crown lens(fig.

^ The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index.

.Even if the object-point on the axis cannot be reproduced quite free from aberration through such a lens, because aberrations of the type of an under-correction have been produced by the first plane outer limiting surface, yet the defects with the strong refraction are relatively small and can be well compensated by other systems.^ Even if the object-point on the axis cannot be reproduced quite free from aberration through such a lens, because aberrations of the type of an under-correction have been produced by the first plane outer limiting surface, yet the defects with the strong refraction are relatively small and can be well compensated by other systems.

^ As the semiaperture of a pencil proceeding from an object point cannot exceed 90°, the numerical aperture of a dry-system cannot be greater than I. On the other hand, in immersion-systems the numerical aperture can almost amount to the refractive index, for A=n sin u Dry systems of o 98 numerical aperture, water immersion (n =1.33) from A =I 25, oil immersion (n =1.51) from A =1.40, and even a-bromnaphthalene immersions ( n =I-65 ) from A =1.60, are available.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

.Amici chiefly employed cemented pairs of lenses consisting of a plano-convex flint lens and a biconvex crown lens(fig.^ Amici chiefly employed cemented pairs of lenses consisting of a plano-convex flint lens and a biconvex crown lens(fig.

^ In the old crown and flint glass a high FIG. 3 i.

^ Similar doublets composed of two piano-convex lenses are the Fraunhofer (fig.

.33),and constructed objectives with an aperture of 135°.^ For this reason Amici constructed objectives of a similar aperture and focus for different thicknesses of glass covers.

^ Hence a condenser, for lighting with very oblique cones, must have about the same aperture as the objective, and therefore be of very wide aperture; they therefore closely resemble microscope objectives in construction.

.He also showed the influence of the cover-slip on pencils of such wide aperture.^ He also showed the influence of the cover-slip on pencils of such wide aperture.

.The lower surface of the slip causes undercorrection on being traversed by the pencil, with over-correction when it leaves it; and since the aberration of the surface lying farthest from the object, i.e. those caused by the upper surface preponderate, an over-corrected cone of rays enters the objective.^ The lower surface of the slip causes undercorrection on being traversed by the pencil, with over-correction when it leaves it; and since the aberration of the surface lying farthest from the object, i.e.

^ But, owing to the various partial reflections which the illuminating cone of rays undergoes when traversing the surfaces of the lenses, a portion of the light comes again into the preparation, and into the eye of the observer, thus veiling the image.

^ The edge which is the separating line of the horizontal and hypothenuse surfaces of the prism, lies approximately over the middle of the system, so that the rays entering through the opening in the side after having been reflected by the hypothenuse surface are concentrated through one half of the objective on to the object.

.The over-correction increases when the glass is thickened.^ The over-correction increases when the glass is thickened.

.In order to counteract this aberration the whole objective must be correspondingly under-corrected.^ In order to counteract this aberration the whole objective must be correspondingly under-corrected.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ When determining the magnification the microscope must be used under exactly the same conditions: neither the length of the tube nor the focal length of the objective may be altered.

.Objectives with definite undercorrection can however only produce really good images with glass covers of a specified thickness.^ Objectives with definite undercorrection can however only produce really good images with glass covers of a specified thickness.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ Schott succeeded, however, in producing glasses which with a comparatively low refraction have a high dispersion, and with a high refraction a low dispersion.

With apertures of o 90-0.95 differences of even o o04 - o o08 in. in the glass covers can be noticed by the deterioration of the image. .In systems with smaller apertures variations of the thickness of the glass cover are not so noticeable.^ In systems with smaller apertures variations of the thickness of the glass cover are not so noticeable.

^ Abbe's test plate consists of an object carrier on which six cover glasses of exactly determined thickness (between 0.09 mm.

^ Especially powerful achromatic condensers are really only magnified microscope objectives, with the difference that they are not corrected for the thickness of the cover slip, but for the thickness of the glass on which the object is placed.

.For this reason Amici constructed objectives of a similar aperture and focus for different thicknesses of glass covers.^ For this reason Amici constructed objectives of a similar aperture and focus for different thicknesses of glass covers.

^ In systems with smaller apertures variations of the thickness of the glass cover are not so noticeable.

^ Abbe's test plate consists of an object carrier on which six cover glasses of exactly determined thickness (between 0.09 mm.

.This expensive method was simplified in 1837 by Andrew Ross by making the upper and lower portion of the objective variable by means of a so-called correction-collar, and so giving the objective a corresponding under-correction according, to the thickness of the glass cover.^ This expensive method was simplified in 1837 by Andrew Ross by making the upper and lower portion of the objective variable by means of a so-called correction- collar , and so giving the objective a corresponding under-correction according, to the thickness of the glass cover.

^ In systems with smaller apertures variations of the thickness of the glass cover are not so noticeable.

^ The objects observed with the vertical illuminator must not have a glass cover if the dry system is employed, because the upper surface of the glass cover would send so much light back into the objective by reflection, that the image would be indistinct.

.The alteration of the focus and the aperture are little influenced.^ The alteration of the focus and the aperture are little influenced.

.The correction-collar was improved by Wenham and Zeiss, by working the upper system upon the lower, and not the reverse; for in this way the preparation remains almost exactly focused during the operation (see fig.^ The correction-collar was improved by Wenham and Zeiss, by working the upper system upon the lower, and not the reverse; for in this way the preparation remains almost exactly focused during the operation (see fig.

^ This expensive method was simplified in 1837 by Andrew Ross by making the upper and lower portion of the objective variable by means of a so-called correction- collar , and so giving the objective a corresponding under-correction according, to the thickness of the glass cover.

^ He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.

34).
.The injurious influence of the glass cover is substantially lessened if no air is admitted to the space between the glass cover and the FIG. 34. - ObjecFIG. 35. - Achro tive fitted with cormatic objective for r e c t i o n collar homogeneous immer (Zeiss).^ Achro tive fitted with cormatic objective for r e c t i o n collar homogeneous immer (Zeiss).

^ The injurious influence of the glass cover is substantially lessened if no air is admitted to the space between the glass cover and the FIG. 34.

^ This expensive method was simplified in 1837 by Andrew Ross by making the upper and lower portion of the objective variable by means of a so-called correction- collar , and so giving the objective a corresponding under-correction according, to the thickness of the glass cover.

sion.
front lens .(as in the dry-system) but if the intervening space is filled with an immersion-liquid.^ A series of objectives with short focal lengths are available, which permit the placing of a liquid between the cover-slip and the front lens of the objective; such lenses are known as " immersion systems "; objectives bounded on both sides by air are called " dry systems."

^ In immersion-systems a very much greater aggregate of rays is used in the representation than is possible in dry-systems.

^ The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index.

.Amici was likewise the first to produce practical and good immersion-systems.^ Amici was likewise the first to produce practical and good immersion-systems.

^ He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.

^ Such systems with a so-called homogeneous immersion were first constructed after the plan of E. Abbe in 1878 in the Zeiss workshops at the instigation of J. W. Stephenson.

The slight difference of the refractive indexes of the glass cover and the immersion-liquid involves a diminution of the aberrations, by which the objective will become less sensitive to the differences in thickness of the glass covers and admits of a more perfect adjustment. Water-immersion was introduced by Amici in 1840, and was improved by E. Hartnack in 1855.
The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index. Such systems with a so-called homogeneous immersion were first constructed after the plan of E. Abbe in 1878 in the Zeiss workshops at the instigation of J. W. Stephenson. Cedarwood oil (Canada balsam), which has a refractive index of 1.515, is the immersion-liquid. The structure of a modern system of this type, with a numerical aperture of I. 30, is shown in fig. 35.
The most perfect microscope objective was invented by E. Abbe in 1886 in the so-called apochromatic objective. .In this, the secondary spectrum is so much lessened that for all practical purposes it is unnoticeable.^ In this, the secondary spectrum is so much lessened that for all practical purposes it is unnoticeable.

.In the apochromats the chromatic difference of the spherical aberrations is eliminated, for the spherical aberration is completely avoided for three colours.^ In the apochromats the chromatic difference of the spherical aberrations is eliminated, for the spherical aberration is completely avoided for three colours.

^ Showing a system with chromatic difference of spherical aberration.

^ The aberrations, both spherical and chromatic, increase very rapidly with the aperture.

.Since in these systems the sine-condition can be fulfilled for several colours, the quality of the images of points beyond the axis is better.^ Under these conditions, the CM-5 takes roughly 1.5 hours to process a four image by ten image section containing thirty-nine overlapping regions.

^ In these cases, the amount of vignetting is severe or the homogeneity of the image in the overlap region is significant.

.There still remains a slight chromatic difference in magnification, for although the magnification consequent upon the fulfilment of the sine-condition is the same for all zones for one colour, it is impossible to avoid a change of the magnification with the colour.^ However, there appears to be less than significant difference between the YAG and phosphor screen scintillators, so this topic remains open.

.Abbe overcame this defect by using the so-called compensation ocular, made with Jena glasses.^ Abbe overcame this defect by using the so-called compensation ocular, made with Jena glasses.

^ The difference of chromatic magnification cannot even be overcome in apochromats, and to cancel this aberration Abbe devised the compensating ocular (fig.

Fig. 36 shows an apochromat of a numerical aperture of 1.40.
.THE Eyepiece Or Ocular The eyepiece is considerably simpler in its construction than the objective.^ THE Eyepiece Or Ocular The eyepiece is considerably simpler in its construction than the objective.

^ The weak compensation oculars resemble a Huygenian eyepiece with achromatic eye-lens, whilst the more powerful ones are of a different construction.

.Its purpose in a microscope is by means of narrow cones of rays to represent at infinity the real magnified image which the objective produces.^ Its purpose in a microscope is by means of narrow cones of rays to represent at infinity the real magnified image which the objective produces.

^ An image is therefore projected by the ocular from the real magnified image produced by the objective with increased magnification.

^ In the commonest compound microscopes, which consist of two positive systems, a real magnified image is produced by the objective.

.As, however, the object represents a real image, the problem is to project a transparent diapositive.^ As, however, the object represents a real image, the problem is to project a transparent diapositive.

^ If we assume that a normal eye observes the image through the eyepiece, the eyepiece must project a distant image from the real image produced by the objective.

^ Double microscopes, which produce a correct impression of the solidity of the object, must project upright images.

.It is therefore impossible to observe this image through an ordinary lens.^ It is therefore impossible to observe this image through an ordinary lens.

^ The image produced by the microscope objective M in its back focus plane is then observed through a supplementary microscope.

^ If we assume that a normal eye observes the image through the eyepiece, the eyepiece must project a distant image from the real image produced by the objective.

.Since many of the rays coming from the exit-pupil of the objective would not reach the eye of the observer at all, it is necessary, in order to make use of all of them, to direct the diverging rays forming the real image so that the whole of the light enters the eye of the observer.^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ Since many of the rays coming from the exit-pupil of the objective would not reach the eye of the observer at all, it is necessary, in order to make use of all of them, to direct the diverging rays forming the real image so that the whole of the light enters the eye of the observer.

^ Both lenses together form the exit-pupil of the objective behind the eyelens, so that this image, the exit-pupil of the total system or the Ramsden circle, is accessible to the eye of the observer.

.This is effected by a collective lens; it may be compared with the second part of the condenser system of a projecting lantern.^ This is effected by a collective lens; it may be compared with the second part of the condenser system of a projecting lantern .

^ To diminish these a collective lens of crown-glass is combined with a dispersing lens of flint; in such a system the red and the blue rays intersect at a point (see Aberration ).

.The two most customary eyepieces consist in two simp:e planoconvex lenses, whose distance one from the other is equal to half the sum of the two focal lengths.^ A, the focal lengths of the objective, and of the eyepiece f2.

^ The two most customary eyepieces consist in two simp:e planoconvex lenses, whose distance one from the other is equal to half the sum of the two focal lengths.

^ One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw .

.One of these is the Ramsden eyepiece (fig.^ One of these is the Ramsden eyepiece (fig.

37). .If the real image produced by the objective coincides with the collective lens, only the inclination of the principal rays is altered, the form of the cone being affected only to a very small extent.^ Since one is therefore forced to use a very small region as the target, it is difficult to produce a good match and its utility is severely restricted.

^ The factors are electromagnet hysteresis (producing an altered magnification), focus variation (inducing an image enlargement and rotation), and variation in stage control (producing an imprecise movement).

^ While this test scenario has shown the method effective, there are instances with other image data that, although very rare, do produce incorrect results.

.The lens nearer the eye, which has about the same focal length as the collective lens, is distant from it by about its focal length.^ The lens nearer the eye, which has about the same focal length as the collective lens, is distant from it by about its focal length.

^ A fixed mark which serves as an index is placed on the lower side of the collective lens and is seen clearly at the same time as the graduation of the movable slide.

^ If f and f' be the focal lengths of the combination, and f2, f2 the focal lengths of the two components, and A the distance between the inner foci of the components, then f = - f,f2/4, f' =fi f27 0 (see Lens ).

.The eye-lens converts diverging pencils into parallels.^ The eye-lens converts diverging pencils into parallels.

^ But as the object-side focus F2 lies behind the eyepiece, the real image is not produced, but the converging pencils from the objective are changed by the eyepiece into parallels ; and the point 0 1 in the top of the object y appears at the top to the eye, i.e.

^ The manner in which the eye uses such a lens was first effectively taken into account by M. von Rohr.

.Both lenses together form the exit-pupil of the objective behind the eyelens, so that this image, the exit-pupil of the total system or the Ramsden circle, is accessible to the eye of the observer.^ This image P"P i " is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system.

^ Both lenses together form the exit-pupil of the objective behind the eyelens, so that this image, the exit-pupil of the total system or the Ramsden circle, is accessible to the eye of the observer.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

.It is possible to see the whole field through this pupil by slightly moving the head and eye.^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ It is possible to see the whole field through this pupil by slightly moving the head and eye.

^ Here also the exit-pupil is accessible to the eye and through it the whole field can be seen by moving the head and eye.

In practice the real image is formed not directly FIG. 37. - Ramsden Eyepiece.
.L2 = collective-, L3 = eye-lens.^ The lens nearer the eye, which has about the same focal length as the collective lens, is distant from it by about its focal length.

^ In this type the eye-lens is about twice as powerful as the collective lens, and makes the rays parallel.

^ L2 = collective-, L3 = eye-lens.

.DD diaphragm of the field of view.^ DD =diaphragm of the field of view.

^ D D = diaphragm of field of view.

^ DD diaphragm of the field of view.

.P"P" = Ramsden's circle, or exit-pupil of whole microscope.^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

^ Here also the exit-pupil is accessible to the eye and through it the whole field can be seen by moving the head and eye.

on the collective lens but a little in front of it, because otherwise all the particles of dust on the collective would also be seen magnified. .In the other type, the Huygenian eyepiece (fig.^ In the other type, the Huygenian eyepiece (fig.

.38), which is much more widely used, the collective lens is in front of the real image; it alters the direction of the principal rays and somewhat diminishes the real image.^ A second kind of dividing prism which directs the entire course of rays to both eyes, and thus produces identical images, was used by Powell and Lealand (fig.

^ He used chiefly a highly curved piano-convex front lens, which has since always been employed in strong systems.

^ If the instrument has a sensible lens diameter, and is arranged so that the centre of rotation of the eye can coincide with the intersection of the principal rays, the lens can then form with the eye a centred system.

.In this type the eye-lens is about twice as powerful as the collective lens, and makes the rays parallel.^ In this type the eye-lens is about twice as powerful as the collective lens, and makes the rays parallel.

^ If the instrument has a sensible lens diameter, and is arranged so that the centre of rotation of the eye can coincide with the intersection of the principal rays, the lens can then form with the eye a centred system.

^ The selection of the rays emerging from the lens and actually employed in forming the image is undertaken by the pupil of the eye which, in this case, is consequently the exit pupil of the instrument.

Here also the exit-pupil is accessible to the eye and through it the whole field can be seen by moving the head and eye. .In both eyepieces micrometers or cross-wires are used for measuring in the plane of the real FIG. 38. - Huygenian Eyepiece.^ In both eyepieces micrometers or cross-wires are used for measuring in the plane of the real FIG. 38.

^ For measuring this angle, an eyepiece with cross-threads is used.

^ In the other type, the Huygenian eyepiece (fig.

.L2 = collective-, L3 = eye-lens.^ The lens nearer the eye, which has about the same focal length as the collective lens, is distant from it by about its focal length.

^ In this type the eye-lens is about twice as powerful as the collective lens, and makes the rays parallel.

^ L2 = collective-, L3 = eye-lens.

.DD =diaphragm of the field of view.^ DD =diaphragm of the field of view.

^ D D = diaphragm of field of view.

^ DD diaphragm of the field of view.

.P"P" = Ramsden's circle, or exit-pupil of whole microscope.^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by headand eye-movements may survey the whole field.

^ Here also the exit-pupil is accessible to the eye and through it the whole field can be seen by moving the head and eye.

image. .The Ramsden eyepiece is the most convenient for this because this plane lies in front of the collective lens, and the objective image has not yet been influenced by the eyepiece.^ The Ramsden eyepiece is the most convenient for this because this plane lies in front of the collective lens, and the objective image has not yet been influenced by the eyepiece.

^ L = front lens of the objective.

^ This is the case if the image O'OI' lies in the front focal plane of the eyepiece.

.As both eyepieces are used with very small apertures (about f : 20) no attempt has been made to overcome the spherical aberrations, which are usually very slight; neither, as a rule, are the eyepieces chromatically corrected, care has only to be taken by a suitable choice of the distance of one lens from the other, that the coloured images derived from a colourless object should have the same apparent size.^ The aberrations, both spherical and chromatic, increase very rapidly with the aperture.

^ By introducing a dispersive lens of flint the magnifying glass could be corrected for both chromatic and spherical aberrations.

^ As both eyepieces are used with very small apertures (about f : 20) no attempt has been made to overcome the spherical aberrations, which are usually very slight; neither, as a rule, are the eyepieces chromatically corrected, care has only to be taken by a suitable choice of the distance of one lens from the other, that the coloured images derived from a colourless object should have the same apparent size.

.Since, however, the difference of chromatic magnification cannot be overcome in powerful objectives, this error is still further increased by the eyepiece.^ Since, however, the difference of chromatic magnification cannot be overcome in powerful objectives, this error is still further increased by the eyepiece.

^ These eyepieces are intentionally provided with a different chromatic magnification, which however is in opposition to that originating in the objective.

^ As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.

.The difference of chromatic magnification cannot even be overcome in apochromats, and to cancel this aberration Abbe devised the compensating ocular (fig.^ The difference of chromatic magnification cannot even be overcome in apochromats, and to cancel this aberration Abbe devised the compensating ocular (fig.

^ Even in apochromats it is not possible to entirely remove the chromatic difference of magnification, i.e.

^ Abbe overcame this defect by using the so-called compensation ocular, made with Jena glasses.

39).
.The weak compensation oculars resemble a Huygenian eyepiece with achromatic eye-lens, whilst the more powerful ones are of a different construction.^ The weak compensation oculars resemble a Huygenian eyepiece with achromatic eye-lens, whilst the more powerful ones are of a different construction.

^ By the supplementary use of one of Wenham's prisms every ray is analysed into a more powerful refracted and a weaker reflected one.

^ Although such systems have been made recently for special purposes, this construction was abandoned, and a more complex one adopted, which also made the production of better objectives possible; this is the principle of the compensation of the aberrations produced in the different parts of the objective.

.These eyepieces are intentionally provided with a different chromatic magnification, which however is in opposition to that originating in the objective.^ These eyepieces are intentionally provided with a different chromatic magnification, which however is in opposition to that originating in the objective.

^ Since, however, the difference of chromatic magnification cannot be overcome in powerful objectives, this error is still further increased by the eyepiece.

^ As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.

.They have also a shorter FIG. 39. - Compensating Eyefocus for red, and a longer one for pieces (Zeiss).^ Compensating Eyefocus for red, and a longer one for pieces (Zeiss).

^ They have also a shorter FIG. 39.

^ A construction also employing one piece of glass forms the so-called Stanhope lens (fig.

blue, and thus magnify the red image more than the blue; and as the objective gives a large blue and a small red image, the two cancel one another and a colourless image is produced.
.These eyepieces are very convenient in use, for when they are changed the lower focus always falls in about the same plane.^ These eyepieces are very convenient in use, for when they are changed the lower focus always falls in about the same plane.

^ These two conditions are only compatible when the representation is made with quite narrow pencils, and where the apertures are so small that the sines and tangents are of about the same value.

^ The Ramsden eyepiece is the most convenient for this because this plane lies in front of the collective lens, and the objective image has not yet been influenced by the eyepiece.

.In German and French microscopes the optical length of the tube, when apochromats and compensation-eyepieces are used, is 180 mm.^ In German and French microscopes the optical length of the tube, when apochromats and compensation-eyepieces are used, is 180 mm.

^ The image viewed through the eyepiece appears then to the observer under the angle w", and as with the single microscope tan w" = I /f 2 ' (4) where f' 2 is the image-side focal length of the eyepiece.

^ This change is usually effected by mounting the objective and eyepiece on two telescoping tubes, so that by drawing apart or pushing in the tube length is increased or diminished at will.

.By multiplying the magnification of the objective by the number .t .^ By multiplying the magnification of the objective by the number .t .

^ The magnification number increases then with the optical tube-length and with the diminution of the focal lengths of objective and eyepiece.

^ The magnification and magnifying number which are most necessary for a microscope with an objective of a given aperture can then be calculated from the formulae: V4 = 2A tan 4'/X; N4 = 2Al tan 4'/A. .

.FIG. 36.- Apochromatic system.^ FIG. 36.- Apochromatic system.

1 _ L3
//
.ID on the eyepiece the total magnification of the microscope is obtained.^ ID on the eyepiece the total magnification of the microscope is obtained.

^ A microscope for two eyes can also be obtained by employing the Abbe stereoscopic eyepiece.

^ To obtain the magnification of the complete microscope we must combine the objective magnification M with the action of the eyepiece.

.By the magnification of the objective is meant the ratio of the distance of distinct vision to the focal length of the objective.^ By the magnification of the objective is meant the ratio of the distance of distinct vision to the focal length of the objective.

^ A, the focal lengths of the objective, and of the eyepiece f2.

^ The focal length of an objective can be more simply determined by placing an objective micrometer on the stage and reproducing on a screen some yards away by the objective which is to be examined.

.As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.^ With these microscopes, which are not stereoscopic, objectives of any power can be used.

^ As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.

^ These eyepieces are intentionally provided with a different chromatic magnification, which however is in opposition to that originating in the objective.

.Illuminating Systems Most microscopic observations are made with transmitted light; an illuminating arrangement is therefore necessary, and as the plane of the object is nearly always horizontal or only slightly inclined, the illuminating rays must be directed along the optical axis of the microscope.^ Illuminating Systems Most microscopic observations are made with transmitted light; an illuminating arrangement is therefore necessary, and as the plane of the object is nearly always horizontal or only slightly inclined, the illuminating rays must be directed along the optical axis of the microscope.

^ If the illuminating pencil is parallel to the axis of the microscope objective, the illumination is said to be direct.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

.To fully utilize the aperture of the system all dispersing rays in the object-space of the objective must be retained in the imagespace of the illuminating system.^ To fully utilize the aperture of the system all dispersing rays in the object-space of the objective must be retained in the imagespace of the illuminating system.

^ A well-corrected microscope objective with a wide aperture therefore can only represent, free from aberrations, one object-element situated on a definite spot on the axis.

^ In dark field illumination care has to be taken that no direct rays reach the objective, and hence a good dark field illumination can be produced if the condenser system has a larger aperture than the objective.

.When this occurs the greatest brightness will be obtained if the corresponding diaphragms of the two systems coincide; i.e. the field-diaphragm on the image-side of the observing system with object-side of the illuminating system, and the exit pupil of the illuminating system with the entrance pupil of the objective.^ Since the exit pupil moves in observing the whole field, the entrance pupil also moves.

^ This image P"P i " is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system.

^ PP1 is the"entrance pupil, P'P1' the exit pupil, and GG the diaphragm.

.For slight magnifications a revolving plane mirror fixed below the object for altering the direction of the rays suffices.^ For slight magnifications a revolving plane mirror fixed below the object for altering the direction of the rays suffices.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ Since, however, only relatively low powers are now employed, the ordinary rack and pinion movement for focusing suffices, and for the illuminating the object only a mirror below the stage is required when the object is transparent, and a condensing lens above the stage when opaque.

.For this mirror to illuminate all the points of the objective so that the rays fill up the objective, it must not be too small, and should be as near as possible to the stage plate, and the source of light must be considerably extended (fig.^ For this mirror to illuminate all the points of the objective so that the rays fill up the objective, it must not be too small, and should be as near as possible to the stage plate, and the source of light must be considerably extended (fig.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ In this case the object lay upon a stage plate, whose centre had so far been made opaque, so that the rays coming from the illuminating plane mirror could not reach the objective direct, but only the rays passing the stage plate to the side of this blackened portion reached the Lieberkiihn mirror, and were used in lighting.

40). .Diffused daylight is very suitable.^ Diffused daylight is very suitable.

^ This is also the most suitable distance when diffused daylight is used, but it is too short with artificial light; the FIG. 40.

.If the aperture of the objective is increased, the diameter of the illuminating surface must also be increased so that the system is quite filled up, from which it follows that this method of illuminating soon fails.^ If the aperture of the objective is increased, the diameter of the illuminating surface must also be increased so that the system is quite filled up, from which it follows that this method of illuminating soon fails.

^ He had recognized that the good operation of a microscope objective depended essentially upon the size of the aperture, and he therefore endeavoured to produce systems with wide aperture and good correction.

^ Then the denominator of the fraction, the numerical aperture, must be correspondingly increased, in order to ascertain the real resolving power.

.The possibilities of illuminating with a concave mirror seem a little more favourable.^ The possibilities of illuminating with a concave mirror seem a little more favourable.

^ Descartes ( Dioptrique, 1637) describes microscopes wherein a concave mirror , with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.

^ By a correct choice of the focal length of the illuminating lens in relation to the focal length of the mirror, it is possible to choose the size of the image of the source of light so that the whole object-field is uniformly lighted.

.As a rule a concave mirror of similar aperture is fitted on the other side of the plane mirror.^ As a rule a concave mirror of similar aperture is fitted on the other side of the plane mirror.

^ As a rule an iris diaphragm, which can be moved sideways, is now fitted below this condenser; below is the mirror which can be moved in all directions.

.With the concave mirror an image of the source of light can be thrown upon the object.