The coverage of a

lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...

is the size of the

image An image or picture is a visual representation. An image can be Two-dimensional space, two-dimensional, such as a drawing, painting, or photograph, or Three-dimensional space, three-dimensional, such as a carving or sculpture. Images may be di ...

it can produce, measured as the diameter of the

image circle The image circle is the cross section of the cone of light transmitted by a lens or series of lenses onto the image plane. When this light strikes a perpendicular target such as photographic film or a digital camera sensor, it forms a circle o ...

produced by the optics. In a

camera A camera is an instrument used to capture and store images and videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photograp ...

system the coverage must be large enough to cover the sensor or film used. In a

view camera A view camera is a large format, large-format camera in which the large format lens, lens forms an erect image, inverted image on a ground glass, ground-glass screen directly at the film plane. The image is viewed, composed, and focused, then the ...

system, because the

film A film, also known as a movie or motion picture, is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are generally, sinc ...

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 In photography and optics, vignetting ( ) is a reduction of an image's brightness or saturation toward the periphery compared to the image center. The word '' vignette'', from the same root as ''vine'', originally referred to a decorative b ...

. Sensors in modern digital cameras come in several sizes. Some popular sizes include " full-frame" or

35mm 35 mm may refer to: Film * 135 film, a type of still photography format commonly referred to as 35 mm film * 35 mm movie film, a type of motion picture film stock * 35MM, a "musical exhibition" by Ryan Scott Oliver that features music ...

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 30.15 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 Optics, optical system is a measure of how strongly the system converges or diverges light; it is the Multiplicative inverse, inverse of the system's optical power. A positive focal length indicates that a system Converge ...

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