Talking about the Image Sensor Format

Image Sensor Format

An image sensor can come in a variety of sizes and formats with the smallest ones used in point and shoot cameras and the largest in professional SLRs. Consumer SLRs often use sensors having the same size as a frame of APS film. Professional SLR cameras occasionally use sensors the same size as a frame of 35mm filmócalled full-frame sensors. (A large format camera uses even larger sensors). Larger image sensors generally have larger photosites that capture more light with less noise. The result is pictures that are clearer, brighter, and sharper. Because the size of photosites is so important, a large 6 Megapixel sensor will often take better pictures than a smaller 8 Megapixel sensor. Not only is noise a problem but smaller sensors also require better, more expensive lenses, especially for wide-angle coverage.

Lenses originally created for 35mm film SLR cameras may appear to mount perfect on DSLR cameras, except the bigger image circle of a 35mm SLR system lens lets superfluous light into the body of the camera, additionally the reduced size of an APS-C image sensor in comparison to the 35mm SLR format results in the image being cropped in comparison to the images created on the SLR film camera. The consequential effect is called field-of-view crop; while the ratio of the format size is called a crop factor or sometimes focal-length multiplier. Updated Review

Sensor size

Larger sensors capture images with less noise and greater dynamic range than smaller sensors. The desirable properties of signal-to-noise ratio and sensor unity gain both scale with the square root of sensor area.

As of April, 2009, many DSLRs have sensor areas around 370 mm2, while many compact camera sensors have one-fifteenth the surface area: a standard 1/2.5" sensor has a surface area of 24.7 mm2. As a result, a typical DSLR will have a signal-to-noise ratio that is nearly 4 times higher than a Digital Camera Review by Gene Wright ().

Because of their larger sensors, DSLRs can generally take high-quality pictures at ISO 1600, 3200, or even higher speeds, while compact cameras tend to produce grainy images even at ISO 400. This problem is exacerbated by pixel count; doubling the number of megapixels on the sensor means that each pixel is half the size, and hence noisier.

Common image sensor formats

Image Sensor Sizes
Relative sizes of the sensors used in most current digital cameras.

Digital SLR formats

As of April 2009, most consumer-level SLRs use sensors around the size of a frame of APS-C film, with a crop factor of 1.5-1.6 or slightly smaller. A notable exception is the Four Thirds System of cameras, mostly made by Olympus, which use smaller sensors with a crop factor of 2.0.

Most DSLR image sensor formats approximate the 3:2 aspect ratio of 35 mm film. Again, the Four Thirds System is a notable exception, with an aspect ratio of 4:3 as seen in most Digital Camera Review by Gene Wrights (see below).

Image Sensor Sizes
Comparison of image sensor sizes, include Nikon DX
Some professional DSLRs use full-frame sensors, equal to the size of a frame of 35 mm film.

Leica offers an "S-System" DSLR with a 45 mm x 30 mm sensor containing 37 million pixels.

Medium-format DSLR

The most common sensor size for medium-format digital cameras is approximately 36 ◊ 48 mm, due to the widespread use of Kodak's 22-megapixel KAF-22000 and 39-megapixel KAF-39000 CCDs in that format.

Compact digital camera formats

Many compact digital cameras use sensors with formats specified in the "inch" system, derived from the outside diameter of the glass envelope of the video camera tube that supported that image size. These formats are often called types, as in "1/2-inch-type CCD, CMOS or Foveon."

Most compact image sensor formats have an aspect ratio of 4:3. This matches the aspect ratio of the popular VGA, SVGA, and XGA display resolutions, allowing images to be displayed on most computer monitors without cropping.

As of April 2009, most Digital Camera use 1/2.5" size sensors. Recent digicams with this sensor size include the Panasonic Lumix DMC-FZ18, Canon PowerShot A570 IS, Canon SD870 IS Digital ELPH (IXUS 860 IS), Sony Cyber-shot DSC-W80, Canon Powershot S5is, Sony Cyber-shot DSC-H7, Canon PowerShot TX1, Sony Cyber-shot DSC-H9, and Casio Exilim EX-V7.

Compact cameras using sensors of nearly twice the area include Fujifilm Finepix s6000fd/ s6500fd (1/1.7"), Fuji Finepix F50fd (1/1.6") and Finepix F31fd (1/1.7"), Canon PowerShot G9 (1/1.7") and SD950 IS (1/1.7"), Ricoh Caplio GX100 (1/1.75"), Nikon Coolpix P5000 (1/1.8"), and some Panasonic Lumix cameras like the DMC-LX3 (1/1.63").

Conversely, the sensors of camera phones are smaller than those of typical compact cameras, allowing greater miniaturization of the electrical and optical components. Sensor sizes of around 1/6" are common in camera phones, as well as in webcams and video digital camcorders.

Table of sensor sizes

Since inch-based sensor formats are not standardized, exact dimensions may vary, but those listed are typical.

Type 1/2.5" 1/1.8" 1/1.7" 1/1.6" 4/3" Canon
APS-C
Nikon
DX
Canon
APS-H
35mm Leica
S2
Kodak
KAF 3900
Diagonal (mm) 7.18 8.93 9.50 10.07 21.6 26.7 28.4 34.5 43.3 54 64
Width (mm) 5.76 7.18 7.60 8.08 17.3 22.2 23.6-.7 28.7 36 45 50.7
Height (mm) 4.29 5.32 5.70 6.01 13.0 14.8 15.5-.8 19.1 24 30 39
Area (mm2) 24.7 38.2 43.3 48.56 225 329 366-374 548 864 1350 1977
Crop factor 6.02 4.84 4.55 4.3 2.00 1.62 1.52 1.26 1.0 0.8 0.68

See also

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