Telephoto lens

A telephoto lens, also known as telelens, is a specific type of a long-focus lens used in photography and cinematography, in which the physical length of the lens is shorter than the focal length.^[1]^: 93 This is achieved by incorporating a special lens group known as a telephoto group that extends the light path to create a long-focus lens in a much shorter overall design. The angle of view and other effects of long-focus lenses are the same for telephoto lenses of the same specified focal length. Long-focal-length lenses are often informally referred to as telephoto lenses, although this is technically incorrect: a telephoto lens specifically incorporates the telephoto group.^[2]^: 207

^ Jacobson, Ralph; Ray, Sidney; Attridge, Geoffrey G.; Axford, Norman (2000-08-17). Manual of Photography. Taylor & Francis. ISBN 978-1-136-09118-6.
^ Smith, Gregory Hallock (2006). Camera Lenses: From Box Camera to Digital. Society of Photo Optical. ISBN 978-0-8194-6093-6.

[JacobsonThe-1] Jacobson, Ralph; Ray, Sidney; Attridge, Geoffrey G.; Axford, Norman (2000-08-17). Manual of Photography. Taylor & Francis. ISBN 978-1-136-09118-6.

[smith-2] Smith, Gregory Hallock (2006). Camera Lenses: From Box Camera to Digital. Society of Photo Optical. ISBN 978-0-8194-6093-6.

[1]

[2]