Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System "classic" size negatives. These negatives were 25.1 × 16.7 mm and had an aspect ratio 3:2.
Sensors meeting these approximate dimensions are used in many digital single-lens reflex cameras, in addition to a few large-sensor live-preview digital cameras (such as the Sony DSC-R1, Sigma DP1 and Leica X1) and a few digital rangefinders (e.g., the Epson R-D1). Such sensors exist in many different variants depending on the manufacturer and camera model. All APS-C variants are considerably smaller than 35 mm standard film which measures 36×24 mm. Sensor sizes range from 20.7×13.8 mm to 28.7×19.1 mm. Each variant results in a slightly different angle of view from lenses at the same focal length and overall a much narrower angle of view compared to 35 mm film. This is why each manufacturer offers a range of lenses designed for its format.
Advantages and disadvantages
Comparing smaller and larger sensors, keeping all other factors the same, image quality increases with a larger sensor due to its higher resolution. Besides yielding a lower resolution (or lower sensitivity), smaller sensors also have other effects. They increase the apparent focal length of the lens, which means that the lens appears to be "longer" (e.g. 450 mm instead of 300 mm). If the lens is not perfect, geometric distortions (near the picture edges in particular) may decrease with a smaller sensor. And of course, camera size, weight and price decrease as sensor size decreases.
Most DSLR and third party lens manufacturers now make lenses specifically designed for APS-C cameras. The designations by brand include:
- Canon: EF-S
- Konica Minolta: DT
- Nikon: DX
- Pentax: DA
- Samsung: NX
- Sigma: DC
- Sony: DT, E
- Tamron: Di II
- Tokina: DX
A crop factor (sometimes referred to as a "focal length multiplier", even though the actual focal length is the same) can be used to calculate the 35 mm equivalent focal length from the actual focal length. The most common multiplier ratios:
- 1.7× — Sigma DP1, Sigma DP2, Sigma SD15, Sigma SD14, Sigma SD10, Sigma SD9, Canon EOS DCS 3†
- 1.62× — Canon EOS 7D, 50D, 60D, 70D, 650D (T4i/X6i), Canon EOS 600D (T3i), 700D (T5i/X7i), 1100D; Canon EOS M
- 1.57x — Nikon D3100, Nikon D3200
- 1.54× — Pentax K-5 II, Pentax K-5†, Pentax K-30, Pentax K-01, Samsung NX
- 1.53× — Pentax K-3, Pentax K10D†, Pentax K200D†
- 1.52× — All Nikon DX format DSLR cameras except Nikon D3100, Nikon D3200, all Fuji, Sony (except for the full-frame α 850,† α 900,† α 99), Sigma SD1, Sigma SD1 Merrill, Sigma DP1 Merrill, Sigma DP2 Merrill
- 1.3×‡ — Canon EOS-1D Mark IV†, 1D Mark III†, 1D Mark II† (and Mark II N), EOS-1D†, Kodak DCS 460†, DCS 560†, DCS 660†, DCS 760†, Leica M8, M8.2
- ‡ A 1.3× Focal Length Multiplier is also known as APS-H. Actual multiplier factor is 1.255x for the 1D Digital, 1.28× for the Canon EOS-1D Mark III and 1.29× for the Canon EOS-1D Mark IV. Leica M8 is 1.33x
APS-C lens formats
Canon, Nikon, Pentax and Sony have developed and designed lenses specifically for their cameras with a lens factor (more fully, lens focal length conversion factor) or "crop factor". APS-C cameras use a smaller area to form the image than traditional 35 mm cameras, and so lenses used on APS-C format cameras have a correspondingly narrower field of view. For example, a 28 mm lens is a wide angle lens on a traditional 35mm camera. But the same lens on an APS-C camera, with a lens factor of 1.6x (relative to a standard full-frame 35mm format camera), has the same angle of view as a 45 mm (28 mm x 1.6 lens factor) lens on a 35 mm camera—i.e. a normal lens. Several third-party lens manufacturers, such as Tamron, Tokina, and Sigma, also manufacture a range of lenses optimised for APS-C sensors.
Canon introduced the Canon EF-S line of lenses in 2003 alongside the 300D. These lenses place the rear of the lens closer to the camera's sensor (referred to as short back focus). This has several benefits, including lighter lenses and a narrower field of view (which implies “longer” zoom). EF-S lenses are compatible with Canon's APS-C digital SLRs, with the exception of the early Canon EOS D30, Canon EOS D60, and Canon EOS 10D, which predated the introduction of the mounting system. EF-S lenses will not physically mount on Canon's full-frame digital or 35mm film SLRs.
Nikon has their DX format for their line of APS-C digital cameras. These can be mounted to all full-frame Nikon digital bodies at the cost of fewer megapixels. These lenses generally exhibit vignetting when mounted on Nikon film bodies, but may be usable at longer focal lengths.
Pentax produces the DA line for their APS-C cameras (the company has yet to introduce a full-frame DSLR). These lenses are available in focal lengths that offer similar field-of-view as lenses previously available for 135 film. The trademark compact design of the DA limited series takes advantage of the smaller APS-C format with the lenses under 40mm and is fully usable on 135 Film with the DA Limited Lenses over 35mm focal length. All DA lenses can be mounted on Pentax film bodies, albeit with increased vignetting. All fixed focal lengths in the rugged DA* series cover 35 film format fully.
Sony has a DT line specifically designed for their APS-C cameras. These lenses can be mounted on any Sony A-mount camera, but are specifically designed for the DSLR-A100 up to DSLR-A700 series of APS-C-format DSLRs, the earlier Konica Minolta 5D and 7D, and the current Alpha SLTs. DT lenses can be mounted on full-frame models like the DSLR-A850, DSLR-A900, or SLT-A99 in "crop" mode, where the frame is cropped and the resolution is roughly halved.
- 35 mm equivalent focal length
- Advanced Photo System
- Crop factor
- Digital versus film photography
- Film format
- Full-frame digital SLR
- Image sensor format
- Image sensor
- Lenses for SLR and DSLR cameras
- List of large sensor interchangeable-lens video cameras
- Bob Atkins: The Future of Digital - Full Frame or APS-C? written in 2004
- Vincent Bockaert: Focal Length Multiplier Digital Photography Review, written in 1998
- Fred Kamphues: The digital crop factor explained, written in 2005
- Zack Smith: SSensor Pixel Size as a Determinant of Digital Camera Image Quality, written in 2007