Zoom lens

A zoom lens is a mechanical assembly of lenses whose focal length can be changed, as opposed to a prime lens, which has a fixed focal length. They are commonly used with still and video cameras, some binoculars and telescopes, and other optical instruments.

Related Topics:
Lenses - Focal length - Prime lens - Still - Video - Camera - Binoculars - Telescope - Optical instrument

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Zoom lenses are sometimes described by the ratio of their longest and shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a "4x" zoom. The term hyperzoom is used to advertise zoom lenses with unconventionally large focal length factors, typically more than 4x and ranging up to 10x (e.g. 35 mm to 350 mm) and even 12x.

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Photographic zoom lenses should not be confused with telephoto lenses, those with large focal lengths. While many zoom lenses provide telephoto capabilities, others are wide-angle zooms, that is, they have shorter than normal focal lengths, and still others are trans-standard zooms covering a range from wide-angle to telephoto.

Related Topics:
Telephoto lens - Wide-angle

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Trans-standard zooms have replaced the fixed focal standard lens on many contemporary cameras.

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The situation is further confused by the fact that some digital cameras use electronic manipulation of the image to increase or decrease its size. This is commonly known as digital zoom and results in a much lower quality image than optical zooming as no more information or detail is gained in the process.

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