Digital camera back

Most digital cameras are built to operate as a self-contained unit. This is especially so at the lower-end, for these cameras usually include zoom lens and flashes that cannot be changed. However, at the highest-end, some digital cameras are nothing but a sophisticated light-sensing unit. Experienced photographers attach these digital "camera backs" to their professional medium format SLR cameras, such as a Hasselblad.

• Area array
  • CCD
  • CMOS
• Linear array
  • CCD (monochrome)
  • 3-strip CCD with color filters

Linear array cameras are also called scan backs.

• Single-shot
• Multi-shot (three-shot, usually)

These camera backs are originally used only in a studio to take pictures of still objects. Most earlier digital camera backs were using linear array sensors which could take seconds or even minutes for a complete high-resolution scan. The linear array sensor acts like its counterpart used in a flatbed image scanner by moving vertically to digitize the image.

Many of these cameras could only capture grayscale images. To take a color picture, it requires three separate scans done with a rotating colored filter. These are called multi-shot backs. Some other camera backs are using CCD arrays similar to typical cameras. These are called single-shot backs.

Since it is much easier to manufacture a high-quality linear CCD array that has only thousands pixels than a CCD matrix that has millions of them, very high resolution linear CCD camera backs were available much earlier than their CCD matrix counterparts. For example, you could buy an expensive camera back with an over 7,000-pixel horizontal resolution in the mid-1990s. However, as of 2004, you can still hardly buy a comparable CCD matrix camera of the same resolution.

Many modern digital camera backs are using very large CCD matrices. This eliminated the need of scanning. For example, Fujifilm produces a 20-million-pixel digital camera back with a 52 mm x 37 mm (2.04" x 1.45") CCD in 2003. This CCD array is a little smaller than a frame of 120 film and much larger than a 35 mm frame (36 mm x 24 mm). In comparison, a consumer digital camera usually uses an itsy-bitsy so-called 1/2.5" or 7.176 mm x 5.329 mm (so-called 1/1.8") CCD sensor. Beware, the 1/2.5" or 1/1.8" diagonal measurement is the size of the entire CCD chip. The actual photo-sensitive area is much smaller.

A digital camera back is a good idea to smooth the transition from film to digital. A photographer can reuse his beloved SLR camera and lens without much trouble. To some medium format camera users, the convienence of a bellows has no substitute. However, there's a catch.

Only a few very expensive high-end digital cameras or camera backs could use film-sized CCDs. Since a camera back's CCD is seldom as large as the film it replaces, either one has to use a smaller CCD, or to use multiple smaller CCDs that form a larger piece. For example, various cameras of the late 1990s based on the "building block" CCDs of Philips use of four to six 12 x 12 mm 1-megapixel CCDs to form larger light sensors.

If a smaller sensor is used, the focal length of the lens shall be adjusted to the actual size of the CCD. For example, when you're using a 35 mm SLR camera with a standard 50 mm lens and a 4/3" digital camera back with a 18.0 mm x 13.5 mm CCD (about half as wide as a 35 mm frame), your 50 mm normal lens becomes a 100 mm telephoto lens. If you want a 50 mm lens, you have to buy a 25 mm wide-angle lens.