A digital camera back is a device that attaches to the back of a camera in place of a film holder and contains an electronic image sensors. This lets cameras that were designed to use film take digital photographs. These backs are generally expensive by consumer standards (US$5000 and up) and are primarily built to be used on the medium- and large-format cameras favored by many professional photographers.
Types
Two sensor back types are commonly used: single shot back (non-scanning) and scan back.
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 or 3-shot backs. As technology advanced single-shot backs became more practical; by 2008 most backs were manufactured were single-shot.
Early backs had to be used tethered by a cable to a controlling computer that would store the images they took. Newer models added the ability to store the photos inside the back itself, and added displays so that the picture could be viewed on the back without requiring a separate computer. Virtually all backs can still be operated in tethered fashion, which allows 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.
Modern high resolution backs that push the limits of data storage and transfer technology still are able to make use of a tethered configuration to offload gigabytes of data to cheaper external storage mediums such as hard drives, instead of the more expensive integrated flash memory.
Single shot back
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 unless specified to be a scan back.
Scan back
Scanning backs operate more like an scanner for paper: they have a linear array of sensors that is moved across the image area to scan the image one row of pixels at a time. Scanning backs are primarily used in large format view cameras.
Advantages and disadvantages
While dedicated digital cameras suitable for advanced use are available, there are advantages in being able to use a film camera to take digital photographs. A single camera can be used for both film and digital photography. Cameras with 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 most medium and all 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 image noise when captured with a 35 mm digital SLR, but exposures of up to about an hour at room temperature and as long as 17 hours in extremely cold situations can remain noise-free on a digital camera back.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 2011, up to 80.1 megapixels) is higher than any digital SLR (in 2011, up to 60.5 megapixels) and captures more detail per pixel due to the omission of ananti-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.
Alternatives
There are alternative ways to create a high-resolution digital image without a digital back.
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