Tele conversion lens

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Digital compact camera with mounted tele attachment. Next to it a wide-angle converter .

A telephoto conversion lens (engl .: tele conversion lens ) is an accessory for photographic or video cameras, with the aid of the focal length of the incorporated lens can be extended.

Tele conversion lenses have a fixed extension factor, they are available with factors between 1.5 to four times the focal length extension. A converter with a factor of two converts a 50 mm lens into a 100 mm telephoto lens , for example .

Tele conversion lenses are primarily used in cine cameras, video cameras and compact digital cameras with permanently installed lenses. If they are used with zoom lenses , they usually only work satisfactorily with the longest set focal length of the basic lens; with other focal lengths there are strong distortions and shadows at the edge of the image, which can develop into a circular image.

Contrary to the name, a telescopic lens is by no means a simple lens, but a multiple lens system that works like a telescope. The beam path is influenced in such a way that the main plane of the basic lens is shifted in the direction of the subject, which corresponds to an extension of the focal length.