Image sensor format

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 narrower angle of view.

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 field of view crop factor, crop factor for short, or focal-length multiplier.

Sensor size

All other things being equal, a larger sensor captures images with greater dynamic range than a smaller sensor. The larger area provides a larger "well" in which photon-freed electrons can accumulate before overflow (highlight clipping) occurs.

As of December 2007, 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: ${\sqrt {370/24.7}}\approx {\sqrt {15}}\approx 3.9$

Notice that noise is reduced as resolution is reduced — all other things equal. In other words, a 1/2.5" sensor that is 12 megapixels will have a lower signal to noise ratio when compared with an 8 megapixel camera with the same sensor.

Common image sensor formats

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

DSLR/MILC formats

Most consumer-level DSLRs and all MILCS / EVILS except one (as of 20 Sep. 2011) use relatively large sensors, either around the size of a frame of APS-C film, with a crop factor of 1.5-1.6; or 30% smaller than that, with a crop factor of 2.0 (this is the Four Thirds System, adopted by Olympus and Panasonic). Some professional DSLRs use full-frame sensors, equal to the size of a frame of 35 mm film. As of September 2011, there only is one MILC camera (Pentax Q) which utilizes a small sensor (1/2.3", a size typical of compact digital cameras: see Compact digital camera formats section below.)

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)
• Canon's APS-H format for high-speed pro-level DSLRs (crop factor 1.3)
• Leica's M8 and M8.2 sensor (crop factor 1.33).
• 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 about thirty full-frame sensors can be produced on an 8 inches (20 cm) silicon wafer that would fit 112 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.

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).

Medium-format DSLR

The most common sensor size for medium-format digital cameras is approximately 48 mm × 36 mm (1.9 in × 1.4 in), due to the widespread use of Kodak's 22-megapixel KAF-22000 and 39-megapixel KAF-39000 CCDs in that format. Phase one offers the P65+ digital back with Dalsa's 53.9 mm × 40.4 mm (2.12 in × 1.59 in) 16-bit sensor containing 60.5 megapixels and Leica offers an "S-System" DSLR with a 45 mm × 30 mm (1.8 in × 1.2 in) sensor containing 37-megapixels. In 2010, Pentax released the 40MP 645D medium format DSLR with a 44 mm × 33 mm (1.7 in × 1.3 in) sensor.

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. David Pogue of the New York Times states that "the actual sensor size is much smaller than what the camera companies publish — about one-third smaller." For example, a camera advertising a 1/2.7" sensor does not have a sensor with a diagonal of 0.37"; instead, the diagonal is closer to 0.26". 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 2010, most compact digital cameras use 1/2.5" or 1/2.3" size sensors. Digicams with the 1/2.5" sensor size include the Panasonic Lumix DMC-FZ18, Canon PowerShot A570 IS, Canon SD870 IS Digital ELPH (IXUS 860 IS), Canon Powershot SX210-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. 1/2.3"-sensor digicams include the Kodak Easyshare M530, the Canon Powershot SX130 IS, the Fuji Finepix Z70, and the Nikon Coolpix S8100.

Many megazoom digicams use 1/2.33" sensors, including the Pentax Optio X90, the Olympus SP600uz, and the Kodak Z981. Additionally, some Sony digicams use a 1/2.4" sensor size, including the Sony Cyber-shot HX5V.

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 G12 (1/1.7") and Powershot SD950 IS and S90/S95(1/1.7"), Ricoh Caplio GX100 (1/1.75"), Nikon Coolpix P5000 (1/1.8") and Coolpix P7000 (1/1.7"), some Panasonic Lumix cameras like the DMC-LX3 and LX5 and the Olympus camera XZ-1(1/1.63"). The largest sensor currently equipping a compact camera should be the one (2/3") on board of Fuji's X-10 (announced on Sep. 1st 2011).

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. The recent Nokia N8 has a sensor size of 1/1.83", however, having the largest sensor in a phone currently.

Table of sensor sizes

Inch-based sensor formats are not standardized. Originally, they were the outer diameters of image tubes used in the 1950s. Exact dimensions may vary, but those listed are typical.

Type	1/8"	1/6"	1/4"	1/3.6"	1/3.2"	1/3"	1/2.7"	1/2.5"	1/2.3"	1/2"	1/1.8"	1/1.7"	1/1.6"	2/3"	Super 16mm	1"	m4/3 · 4/3" (Four Thirds)	Sigma Foveon X3	Canon APS-C	Sony · Pentax · Sigma · Samsung APS-C / Nikon DX	Canon APS-H	35mm Full-frame / Nikon FX	Leica S2	Pentax 645D	Kodak KAF 39000 CCD	Leaf AFi 10	Phase One P 65+
Diagonal (mm)	2.00	3.00	4.00	5.00	5.68	6.00	6.72	7.18	7.7	8.00	8.93	9.50	10.07	11.0	14.54	16.0	21.6	24.9	26.7	28.2-28.4	33.5	43.2-43.3	54	55	61.3	66.57	67.4
Width (mm)	1.60	2.40	3.20	4.00	4.54	4.80	5.37	5.76	6.16	6.40	7.18	7.60	8.08	8.80	12.52	12.8	17.3	20.7	22.2	23.6-23.7	27.9	36	45	44	49	56	53.9
Height (mm)	1.20	1.80	2.40	3.00	3.42	3.60	4.04	4.29	4.62	4.80	5.32	5.70	6.01	6.60	7.41	9.6	13.0	13.8	14.8	15.6	18.6	23.9-24	30	33	36.8	36	40.4
Area (mm2)	1.92	4.32	7.68	12.0	15.5	17.3	21.7	24.7	28.5	30.7	38.2	43.3	48.56	58.1	92.8	123	225	286	329	368-370	519	860-864	1350	1452	1803	2016	2178
Crop factor	21.65	14.14	10.83	8.65	7.61	7.21	6.44	6.02	5.62	5.41	4.84	4.55	4.3	3.93	2.97	2.70	2.00	1.74	1.62	1.52-1.54	1.29	1.0	0.8	0.78	0.71	0.65	0.64

Bridge cameras and ... bridging the gap in sensor sizes

This semi-logarithmic graph shows the large gap between compact digital and DSLR camera sensor sizes. The x axis is a discrete set of sensor format sizes used in digital cameras, not a linear measurement axis.

There still is a large gap in sensor size between digital compact cameras and either DSLR or bridge cameras. In fact current compact cameras sensors are smaller than 1/1.6" (48.5 mm²), while the smallest sensor size found in DSLRs and bridge cameras is 4/3" (225 mm²). The main reason for such a gap is portability: large sensors imply the need of large lenses (to provide large images without too many oblique rays hitting the sensor). That's why current bridge cameras tend to show a marked disproportion between their tiny bodies and their huge lens systems (their zoom objectives especially). Lately the above mentioned gap started to be closed, though, by new camera models. For instance, a very large (for a compact) 2/3" (58.1 mm²) sensor is equipping the high-end compact announced by Fuji on Sep. 1st 2011 (Fuji X10).

Since 2005, there has been an increasing interest in bridge cameras, medium-sized cameras with large sensors but without the mirror systems and - consequently - the bulk typical of DSLR camera bodies. Manufacturers have gradually responded to this interest. Epson, an early entrant, introduced the R-D1, a digital rangefinder using the Leica M mount. Other companies followed suit, by introducing similar cameras that focus electronically rather than manually (such as Olympus, with its PEN series; Panasonic, with its G and GF series; Sony, with its Nex series; Samsung, with its NX series; Fujy, with its X100). Such cameras might overall look like compact digital ones, with at least two notable differences: a sensor (either Four Thirds or APS-C) of the size found in digital SLRs, and interchangeable lenses. The latter feature, though, is now to be found in at least one small-sensor compact camera as well (Pentax Q, announced on June 2011).

See also

• Full-frame digital SLR
• Sensor size and angle of view
• 35 mm equivalent focal length
• Film format

External links

• 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