Telephoto lens

In photography and cinematography, a telephoto lens is a lens whose focal length is significantly longer than the focal length of a normal lens. For a 35 mm camera with a 36 mm by 24 mm format, the normal lens is 50 mm and a lens of focal length 70 mm or more is considered telephoto. On the 6x6 cm format (120 film) the normal lens is 80 mm, and focal lengths above 100 mm are considered telephoto.

Related Topics:
Photography - Cinematography - Lens - Focal length - Normal lens - 35 mm - Camera - Mm - 120 film

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Telephoto lenses are best known for making distant objects appear larger. This effect is similar to moving closer to the object, but is not the same, since a telephoto will produce a different perspective. Telephoto lenses also have less depth of field at a given aperture than shorter lenses.

Related Topics:
Perspective - Depth of field

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Regarding optical design a telephoto lens must contain a telephoto group, which allows the lens to be physically shorter than its focal length. A lens with a conventional design and a focal length longer than a normal lens should properly be referred to as long focus. Still, common nomenclature simply refers to all long-focus lenses as telephoto.

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Compare with the opposite effect used in retrofocus lenses (sometimes designed as inverted telephotos), which have greater clearance from the rear element to the film plane than their focal length would permit with a conventional optical design.

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