Long-focus lens

In photography, a long-focus lens is a camera lens which has a focal length that is longer than the diagonal measure of the film or sensor that receives its image.^[1]^[2] It is used to make distant objects appear magnified with magnification increasing as longer focal length lenses are used. A long-focus lens is one of three basic photographic lens types classified by relative focal length, the other two being a normal lens and a wide-angle lens.^[3] As with other types of camera lenses, the focal length is usually expressed in a millimeter value written on the lens, for example: a 500 mm lens. The most common type of long-focus lens is the telephoto lens, which incorporate a special lens group known as a telephoto group to make the physical length of the lens shorter than the focal length.^[4]

^ Sidney F. Ray (2002). Applied photographic optics: lenses and optical systems for photography (3rd ed.). Focal Press. p. 294. ISBN 978-0-240-51540-3.
^ R. E. Jacobson (2000). The manual of photography: photographic and digital imaging (9th ed.). Focal Press. p. 93. ISBN 978-0-240-51574-8.
^ Bruce Warren (2001). Photography (2nd ed.). Delmar Thomson (Cengage) Learning. p. 71. ISBN 978-0-7668-1777-7.
^ Bernard Edward Jones (1911). Cassell's cyclopaedia of photography (2nd ed.). Ayer Publishing. p. 537. ISBN 978-0-405-04922-4.

[1] Sidney F. Ray (2002). Applied photographic optics: lenses and optical systems for photography (3rd ed.). Focal Press. p. 294. ISBN 978-0-240-51540-3.

[2] R. E. Jacobson (2000). The manual of photography: photographic and digital imaging (9th ed.). Focal Press. p. 93. ISBN 978-0-240-51574-8.

[3] Bruce Warren (2001). Photography (2nd ed.). Delmar Thomson (Cengage) Learning. p. 71. ISBN 978-0-7668-1777-7.

[4] Bernard Edward Jones (1911). Cassell's cyclopaedia of photography (2nd ed.). Ayer Publishing. p. 537. ISBN 978-0-405-04922-4.

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