The coverage of a lens is the size of the

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...

it can produce, measured as the diameter of the image circle produced by the optics. In a camera system the coverage must be large enough to cover the sensor or film used. In a view camera system, because the

film A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...

plane can be moved independently of the lens plane, the lens must have enough coverage to cover the film while it is offset from the center of the coverage area. Inadequate coverage can lead to vignetting. Sensors in modern digital cameras come in several sizes. Some popular sizes include " full-frame" or 35mm,

APS-C Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System film negative in its C ("Classic") format, of 25.1×16.7 mm, an aspect ratio of 3:2 and Ø 31.15 mm field d ...

, and 1-inch. Lenses are often intended to work with one of these sensor formats, but in some cases a lens can be used with multiple formats. A “full-frame” type lens produces an image circle that is large enough to cover a 35mm sensor. Because APS-C sensors are smaller than 35mm sensors a full frame lens should be compatible with an APS-C sensor. An APS-C type lens often does not have the coverage to cast light on the entirety of a 35mm sensor, causing dark corners in the images. Photo_lenses_with_a_focal_length_and_angle

Photo_lenses_with_a_focal_length_and_angle

One common misconception about lenses is that

focal length The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foca ...

determines the angle of view for a lens, when in reality it is a combination of focal length, lens coverage, and sensor size. A lens of a certain focal length on a large sensor will yield a wider angle of view than the same lens used with a smaller sensor.

References

Science of photography {{Photo-stub