Sensor size and angle of view

Cameras with digital image sensors that are smaller than the typical 35mm film size have a smaller field or angle of view when used with a lens of the same focal length. This is because angle of view is a function of both focal length and the sensor or film size used. If a sensor smaller than the full-frame 35mm film format is used, as in most digicams, then the field of view is cropped by the sensor to smaller than the 35mm full-frame format's field of view. This narrowing of the field of view is often described in terms of a focal length multiplier or crop factor, a factor by which a longer focal length lens would be needed to get the same field of view on a full-frame camera. The result is geometrically similar to taking the image from the film camera and cutting it down (cropping) to the size of the sensor, ignoring various questions such as resolution. For moderately large DSLRs the crop factor may be in the range of 1.3-2 while smaller cameras use smaller sensors with a larger crop factor. If the digital sensor has a higher or lower density of pixels per unit area than the film equivalent, then the amount of information captured differs correspondingly. While resolution can be estimated in pixels per unit area, the comparison is complex since most types of digital sensor record only a single colour at each pixel location, and different types of film have different effective resolutions. There are various trade-offs involved, since larger sensors are more expensive to manufacture and require larger lenses, while sensors with higher numbers of pixels per unit area are likely to suffer higher noise levels. For these reasons, it is possible to obtain cheap digital cameras with sensor sizes much smaller than 35mm film, but with high pixel counts, that can still produce high-resolution images. Such cameras are usually supplied with lenses that would be classed as extremely wide angle on a 35mm camera, and that can also be smaller size and less expensive, since there is a smaller sensor to illuminate. For example, a camera with

1/1.8" sensor has a 5.0x field of view crop, and so a hypothetical 5-50mm zoom lens produces images that look similar (again the differences mentioned above are important) to those produced by a 35mm film camera with a 25Ц250mm lens, while being much more compact than such a lens for a 35mm camera since the imaging circle is much smaller. This can be useful if extra telephoto reach is desired, as a certain lens on an APS sensor produces an image equivalent to a significantly longer lens on a 35mm film camera shot at the same distance from the subject, the equivalent length of which depends on the camera's field of view crop. This is sometimes referred to as the focal length multiplier, but the focal length is a physical attribute of the lens and not the camera system itself. The disadvantage of this is that wide angle photography is made somewhat more difficult, as the smaller sensor effectively and undesirably reduces the captured field of view. Some methods of compensating for this or otherwise producing much wider digital photographs involve using a fisheye lens and "defishing" the image in post processing to simulate a rectilinear wide angle lens. Full-frame digital SLRs, that is, those with sensor size matching a frame of 35mm film, include Canon 1D X, 1Ds and 5D series, and 6D; Kodak Pro DCS-14n; Nikon D3, D4, D600, D700 and D800 lines; and Contax N Digital. There are very few digital cameras with sensors that can approach the resolution of larger-format film cameras, with the possible exception of the Mamiya ZD (22MP), the Hasselblad H3D series of DSLRs (22 to 39 MP), and the Nikon D800 (36 MP). Common values for field of view crop in DSLRs include 1.3x for some Canon (APS-H) sensors, 1.5x for Sony APS-C sensors used by Nikon, Pentax and Konica Minolta and for Fujifilm sensors, 1.6 (APS-C) for most Canon sensors, ~1.7x for Sigma's Foveon sensors and 2x for Kodak and Panasonic 4/3" sensors currently used by Olympus and Panasonic. Crop factors for non-SLR consumer compact and bridge cameras are larger, frequently 4x or more.