APS-C

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Advanced Photo System type-C (APS-C) is a type of sensor used in many digital single-lens reflex cameras, in addition to a few large-sensored Live-Preview Digital cameras (e.g. the Sony DSC-R1 and the Sigma DP1) and a few digital rangefinders (e.g. the Epson R-D1). This sensor exists in many different standards or variants depending on the manufacturer and camera model[1]. All APS-C variants are smaller than the 35mm standard size of 36 x 24 mm, ranging from 20.7 x 13.8 mm to 28.7 x 19.1 mm. And each variant result in a different field of view (FOV) from the same lens at the same focal length when the lens is interchanged on camera bodies of different sensor sizes. A focal length multiplier (FLM) is used to calculate the 35mm equivalent focal length from the actual focal length when the lens is used on a body of a variant APS-C sensor size (for example using a 17 mm lens on a camera body with an APS-C of 22.2 x 15.7 mm will result in an FLM of (36 mm divided by 22.2 mm = 1.6 approximately), hence that lens will be approximately (equivalent to 17 mm x 1.6 = 28 mm on a 35mm camera). This way of calculating a standard 35mm equivalent makes it possible to know what kind of FOV the photographer can expect from a given lens mounted on a body of a given sensor size (so that if the equivalent is 28mm for example, it always means a wide angle producing the same FOV of a 28mm lens on a 35mm camera).

Several manufacturers now make lenses specifically designed for APS-C cameras. These include Canon's EF-S line, Nikon's DX, Pentax's DA line, and Sigma's DC line.

[edit] Multiplier factors

The most common multiplier ratios (in order of announcements):

(* discontinued)

[edit] Lens differences, incompatibilities

Lenses with 1.6x multiplier - also called crop - such as the Canon EF-S line, place the rear of the lens closer to the camera's sensor (referred to as Short Back Focus). This has several benefits, including increasing the focal range. It also has downsides, in that the lenses aren't compatible with camera bodies that use a full-size mirror, as it would damage the mirror, and thus the lenses can't be used on other digital or analog bodies.

Cameras capable of using short-back lenses include the Canon EOS 300D and 350D - also known as Digital Rebel and Digital Rebel XT; and more recently the EOS 400D, also known as the digital Rebel XTi - as well as the 20D and its latest successor, the 30D. These cameras support conventional 35 mm lenses as well.

[edit] External links

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