Image sensor format

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Comparison of different image sensor sizes

In digital photography, the image sensor format is the shape and size of the image sensor.

The image sensor format of a digital camera determines the angle of view of a particular lens when used with a particular camera. In particular, image sensors in digital SLR cameras tend to be smaller than the 24 mm x 36 mm image area of full-frame 35 mm cameras, and therefore lead to a more narrow angle of view. For a given number of pixels in a sensor, a larger image sensor typically produces higher-quality images because the individual pixels have a larger size (see below).

Lenses produced for 35 mm film cameras may mount well on the digital bodies, but the larger image circle of the 35 mm system lens allows unwanted light into the camera body, and the smaller size of the image sensor compared to 35 mm format results in cropping of the image compared to the results produced on the film camera. This latter effect is known as field-of-view crop; the format size ratio is known as the crop factor or focal-length multiplier.

[edit] Sensor size

All other things being equal, 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.^[1]

As of December 2007^[update], 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. Thus, a typical DSLR will have a signal-to-noise ratio that is nearly 4 times higher than a typical compact digital camera ().

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 pixels on the sensor means that each pixel is half the size, and hence noisier.

[edit] Common image sensor formats

Sizes of the sensors used in most current digital cameras relative to a standard 35mm frame.

[edit] Digital SLR formats

As of June 2009^[update], 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. 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. Some professional DSLRs use full-frame sensors, equal to the size of a frame of 35 mm film. Many different terms are used in marketing and describing these sensor formats, including the following:

• Full-frame digital SLR format, with sensor dimensions nearly equal to those of 35 mm film (36 × 24 mm)
• Leica's M8 and M8.2 sensor (crop factor 1.33).
• Canon's APS-H format for high-speed pro-level DSLRs (crop factor 1.3)
• APS-C refers to a range of similarly-sized formats, including
  • Nikon DX format, Pentax, Konica Minolta/Sony α, Fuji (crop factor 1.5)
  • Canon entry-level DSLR formats (crop factor 1.6)
• Foveon X3 format used in Sigma SD-series DSLRs (crop factor 1.7)
• Four Thirds System format (crop factor 2.0)

Production costs for a full frame sensor can exceed twenty times the costs of an APS-C sensor. Only 20 full frame sensors can be produced on a 8 inches (20 cm) silicon wafer that would fit 200 APS-C sensors and there is a significant reduction in yield due to the large area for contaminants per component. Additionally, the full frame sensor requires three separate exposures during the photolithography stage, which requires separate masks and quality control steps. The APS-H size was selected since it is the largest that can be imaged with a single mask to help control production costs and manage yields.^[2]

Due to the ever-changing constraints of semiconductor fabrication and processing, and because camera manufacturers often source sensors from third-party foundries, it is common for sensor dimensions to vary slightly within the same nominal format. For example, the Nikon D3 and D700 cameras' nominally full-frame sensors actually measure 36 × 23.9 mm, slightly smaller than a frame of 35 mm film. As another example, the Pentax K200D's sensor (made by Sony) measures 23.5 × 15.7 mm, while the contemporaneous K20D's sensor (made by Samsung) measures 23.4 × 15.6 mm.

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 compact digital cameras (see below).

[edit] 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.

Leica offers an "S-System" DSLR with a 45 mm x 30 mm sensor containing 37 million pixels.^[3]

[edit] Compact digital camera formats

The sensor sizes of many compact digital cameras are expressed in terms of the non-standardized "inch" system, as approximately 1.5 times the length of the diagonal of the sensor. This goes back to the way image sizes of early video cameras were expressed in terms of the outside diameter of the glass envelope of the video camera tube.^[4] Instead of "formats", these sensor sizes are often called types, as in "1/2-inch-type CCD." Most compact image sensors 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 December 2007^[update], most compact digital cameras 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 digital camcorders.

[edit] Table of sensor sizes

Since inch-based sensor formats are not standardized, exact dimensions may vary, but those listed are typical.^[4]

[edit] See also

• 35 mm equivalent focal length
• Digital photography#Sensor size and angle of view
• Film format

[edit] Notes and references

[edit] External links

• Pixel Size as a Determinant of Digital Camera Image Quality
• Compact Camera High ISO modes: Separating the facts from the hype (May 2007)
• The «Mass» of Pixels or the «Mess» of Pixels? at 6mpixel.org