A digital camera back is a device which attaches to the back of a camera in place of a film holder and contains an electronic image sensor. This lets cameras which were designed to use film take digital photographs. These backs are generally expensive by consumer standards ($5000 and up) and are primarily built to be used on the medium-format or large-format cameras favored by many professional photographers.
Two sensor arrangements are commonly used: scanning and non-scanning. Non-scanning backs have a sensor similar to that used in most other digital cameras, a square or rectangular array of pixels. Backs are generally assumed to be non-scanning. Scanning backs operate more like a typical scanner for paper; they have a thin imaging sensor that is moved across the image area.
Some backs, primarily older ones, require multiple exposures to capture an image; generally one each for red, green, and blue. These are called multi-shot backs, or more typically, 3-shot backs. As technology advanced, Single Shot backs became more practical; most backs made as of 2008 are single-shot and non-scanning.
Early backs had to be used in a tethered fashion in which they had a cable running to a controlling computer which would store the images they took. Newer models have added the ability to store the photos inside the back itself, and added displays so that the picture could be viewed on the back as opposed to requiring a separate computer. Virtually all backs can still be operated in a tethered fashion, which allows for convenient previewing of images on a large monitor by several people at the same time, sophisticated control of camera functions, and convenient storage for the large image files produced.
While digital cameras suitable for advanced use are available, there are advantages in being able to use a film camera to take digital photographs. On the one hand, a single camera can be used for both film and digital photography; on the other, cameras with advanced features not available on digital cameras (e.g., view cameras) can be used to make digital images.
Digital backs which are used in place of the normal film back are available for all medium- and large-format cameras with adaptors which can allow the same digital camera back to be used with several different cameras, allowing a photographer to choose a body/lens combination best suited for each application rather than using a body/lens system which represents a compromise of design to fit a variety of applications.
Users with large investments in existing camera equipment can convert it to digital use, both saving money and allowing them to continue to use their preferred and familiar tools.
Exposures longer than several minutes are obscured by noise when captured with a 35 mm digital SLR but can remain noise free on a digital camera back for an hour at room temperature and as long as 17 hours in extremely cold situations . In practice a 30 second exposure on a Sinar 75 evolution  with a built in fan assisted Peltier cooled CCD represents the state of the art for practical purposes.
The resolution of digital camera backs (in 2008, up to 60 megapixels) is higher than any 35 mm digital SLR (in 2008, 24.6 megapixels) and captures more detail per pixel due to the omission of an anti-aliasing filter. Each pixel is also able to capture more dynamic range due to higher quality electronics and larger pixel pitch. The use of active cooling systems such as internal fans and Peltier effect electric cooling systems also contributes to image quality.
Before purchasing a digital back, it is worth considering that an alternative way to create a high-resolution digital image is to take a photograph on film with a large-format camera, and scan the result. This can be used to create a much larger very high resolution computer file than is feasible with a single-shot digital back., though it has been argued that the true resolution difference is not as great as might be presumed.
Another alternative is to take multiple pictures with a smaller digital camera, such as a DSLR, and then stitch them together via image stitching. In this way very high resolution images can be produced from a low-resolution sensor, though the process can be lengthy and is unsuited for moving subjects.
Early digital camera backs created huge amounts of data relative to the available storage media and had to be connected (tethered) to a computer during capture.
Many earlier multi-shot backs could natively capture only grayscale images; color images were created by scanning three times through colored filters which rotated into place.
Later, one-shot digital backs were released, which can work at all shutter speeds even on motorized medium-format cameras. Images are stored on fast high-capacity memory cards, making the backs usable wherever film can be used.
Historically the Digital Camera Back market was dominated by linear-scan models (as opposed to single-shot models). These use moving linear array sensors which take seconds or even minutes for a complete high-resolution scan. The linear array sensor acts similarly to a flatbed image scanner by moving to digitize the image. Consequently these backs are only suitable for photographing static subjects.
Since it is much easier to manufacture a high-quality linear (one-dimensional) CCD array that has only a few thousand pixels than a two-dimensional CCD matrix that has millions, very high resolution linear CCD camera backs were available much earlier than their CCD matrix counterparts. For example, camera backs with a 7,000-pixel linear resolution—capable of producing pictures of about 40 megapixels—were available in the mid-1990s.
The digital camera is one of the most remarkable instances of this shift because it is so truly different from its predecessor. Conventional cameras depend entirely on chemical and mechanical processes -- you don't even need electricity to operate them. On the other hand, all digital cameras have a built-in computer, and all of them record images electronically.
As of 2008 CCD matrix camera backs of 39 megapixel using the Kodak CCD and 33 megapixel Dalsa CCD in the Sinar 75 and in the Leaf Aptus 75 (6726 x 5040 pixels, with 7.2 micrometre wide pixels). In development by several camera manufactures are larger camera backs based on the Kodak 50 megapixel CCD. Scanning backs are currently a narrower niche, used only for the highest quality images or with large-format cameras. Sinar continues their development of the step and repeat system of extending the CCD capabilities (macroscanning) with the arTec camera which creates a panoramic image with stitching technology.
Image sensors have gotten physically larger; Kodak has produced a 50-million-pixel CCD which is 49.1 mm × 36.85 mm (1.93" x 1.45"). This CCD array approaches the size of a frame of 120 film (60 mm × 45 mm) and is twice the size of a 35 mm frame (36 mm x 24 mm), and over seventy times the size of the typical 1/1.8" (7.2 mm x 5.3 mm) sensor size used in point-and-shoot pocket cameras. This type of very large surface CCD is currently in use by the leading brands in high resolution photography. Other recent innovations are built in LCD viewing screens and the inclusion of all processing within the camera back with output in open DRG file format, such as the Sinar 65.
The first commercial digital camera back was introduced by Leaf (now part of Kodak) in 1991. The Leaf DCBI (Digital Camera Back I), nicknamed 'The Brick', offered resolution of 4 million pixels (MP) in a 2048×2048 pixel format the same CCD was used by Sinar in its equivalent sinarback. In 1994 Leaf introduced an improved model, the DCBII, which included a live-video view, and in 1998 they introduced the 6MP Volare.
A complete camera system was constructed using the Sinar view camera system with a Sinarcam 1 shutter system which provided control of the live image, and an adapter plate was made to use the backs with Hasselblad cameras. Driver software generally required the use of an Apple Macintosh to operate the cameras.
These systems were complex and expensive. They used custom controller cards (known as the "SCSI taxi"), and were 3-shot backs; a colored filter wheel inside the back rotated to take red, green, and blue exposures.
Competition soon came to the new industry.
MegaVision in 1992 introduced their T2 back, which was a similar product; it also was a 3-shot unit with a 4MP square sensor. MegaVision had been making digital photography equipment based on video technology since 1984, and the T2 had live video preview.
Phase One was founded in 1993, and by 1994 was selling their StudioKit scanning backs. In 1998 Phase One launched the Lightphase. which was the first one-shot back that could compete with film in terms of quality. Resolution was 6 megapixels and the physical size of the CCD was full-frame 35mm, however the back was designed to be used on Hasselblad 500-series cameras.
Other early industry entrants included Jenoptik who produced products in cooperation with Sinar, Dicomed (a scanning back maker which closed in 1999), Better Light (the most prominent scanning back maker), and Kigamo.
By 2003, Leaf had an 11MP model, the Valeo, and Jenoptik/Sinar had the 11MP Sinarback 43. several vendors had 16MP models; Kodak produced the $15,000 16MP Pro Back Plus using their own CCD, Imacon made the ixpress 96, Phase One had their H20 and Sinar continued its cameraback development from the 22, 23h, 43h and issued the 44H which when mounted on a macroscan unit delivered an image of over 1 Gb in size with live image focussing using the Sinarcam shutter system.
By 2009 Phase One is the market leader with their own camera manufacturing and the P65+, which is at the time the only full-frame 645 camera back.
In the middle 2000s, the digital back market began to change and consolidate quickly with two trends taking place. Medium-format film cameras are being displaced by digital single-lens reflex cameras based on smaller, 35 mm film cameras, which can offer high quality results with no more expense than medium-format film gear and the ease of digital workflow. This is leading to the development of all-digital medium-format cameras which do not need separate digital backs.
Bronica and Contax, formerly two of the largest medium-format camera makers, have gone out of business. Fuji has ceased production of their 680 medium-format film cameras. Mamiya crossed the product line divide in 2004, announcing a medium-format digital camera, the Mamiya ZD. The imaging technology used in this camera is also available as a separate digital back, the ZD Back, which can be used with Mamiya's film cameras. Shortly after the product was announced, the company was sold. Pentax, whose cameras cannot use digital backs, announced a medium-format digital camera in 2005, but have yet to place it on sale.
The second trend is the release of new camera systems designed to tightly integrate with digital backs; this provides users with the ability to use film but also makes the camera easier to use than a film camera which has no communication with the separate digital back.
Under pressure from digital camera back manufacturers, Hasselblad was eventually merged with back maker Imacon under the Hasselblad name. The new post-merger Hasselblad worked with Fuji to develop a new line of cameras (Hasselblad's first in over 50 years) designed to closely integrate with digital backs, particularly the former Imacon models. This meant that Shriro (owner of Hasselblad/Imacon) and Fuji could squeeze out other back makers, sending those manufacturers (and the remaining medium-format manufacturers) seeking their own partnerships.
Mamiya has announced a partnership with Phase One, This has later developed in to Phase One buying a major stake in Mamiya Jenoptik commissioned Rollei to work with Sinar to develop their own tightly integrated platform, the Hy6. The Hy6 is also marketed by Leaf under their name and using their backs. The Sinar HY6 keeps the unique facilities of the rotating cameraback and live image functionality
During this process, several product lines of digital backs have been discontinued. Kodak stopped making their own backs in 2004, shortly before purchasing Leaf. Fuji had their own line of backs, but certainly only one product line will be produced by Fuji and Hasselblad together leaving the Jenoptik / Sinar group as the only European digital medium-format and view camera manufacturer.