Digital Camera - Digital Camera Backs

Digital Camera Backs

In the industrial and high-end professional photography market, some camera systems use modular (removable) image sensors. For example, some medium format SLR cameras, such as the Mamiya 645D series, allow installation of either a digital camera back or a traditional photographic film back.

• 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)

Most earlier digital camera backs used linear array sensors. The linear array sensor acts like its counterpart in a flatbed image scanner by moving vertically to digitize the image. Many early such cameras only capture grayscale images. Color photography requires three separate scans, and a mechanical assembly to cycle a primary color filter in front of the sensor. These are called multi-shot backs. The entire scanning process requires relatively long expsoure times, in the range of seconds or even minutes. Due to this relatively long exposure-time, scanning and mutli-shot backs are generally limited to studio applications, where all aspects of the photographic scene are under the photographer's control.

Some other camera backs use 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 with only thousands of pixels than a CCD matrix with millions, very high resolution linear CCD camera backs were available much earlier than their CCD matrix counterparts. For example, you could buy an (albeit expensive) camera back with over 7,000 pixel horizontal resolution in the mid-1990s. However, as of 2004, it is still difficult to buy a comparable CCD matrix camera of the same resolution. Rotating line cameras, with about 10,000 color pixels in its sensor line, are able, as of 2005, to capture about 120,000 lines during one full 360 degree rotation, thereby creating a single digital image of 1,200 Megapixels.

Most modern digital camera backs use CCD or CMOS matrix sensors. The matrix sensor captures the entire image frame at once, instead of incrementing scanning the frame area through the prolonged exposure. For example, Phase One produces a 39 million pixel digital camera back with a 49.1 x 36.8 mm CCD in 2008. This CCD array is a little smaller than a frame of 120 film and much larger than a 35 mm frame (36 x 24 mm). In comparison, consumer digital cameras use arrays ranging from 36 x 24 mm (full frame on high end consumer DSLRs) to 7.2 x 5.3 mm (on point and shoot cameras) CMOS sensor.

Relatively few complete digital SLR cameras have sensors large enough to compete (except by image stitching) with the image detail offered by medium to large format film cameras. Phase One, Mamiya, and Hasselblad in 2011 manufacture medium format digital devices that can capture 30MP up to 80MP. These large and expensive cameras, having high build quality and few moving parts, tend to be long lasting and are prominent on the used market.