Normal lens
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In photography and cinematography a normal lens is a lens that generates images that are generally held to have a "natural" perspective compared with lenses with longer or shorter focal lengths.
Lenses of shorter focal length are called wide-angle lenses, while longer focal length lenses are called telephoto lenses.
In still photography, a normal lens is a lens whose focal length is roughly equivalent to the diagonal of the image projected within the camera. This roughly approximates the perceived field of view of the human eye.
Standard normal lenses for various film formats for photography are:
| Film format | Image dimensions | Image diagonal | Normal lens focal length |
|---|---|---|---|
| APS C | 1.67 cm x 2.51 cm | 30.15 mm | 28 mm, 35 mm |
| 135 | 2.4 cm x 3.6 cm | 43.27 mm | 50 mm, 45 mm |
| 120/220, 6 x 4.5 (645) | 5.6 cm x 4.2 cm | 70.00 mm | 75 mm |
| 120/220, 6 x 6 | 5.6 cm x 5.6 cm | 79.20 mm | 80 mm |
| 120/220, 6 x 7 | 5.6 cm x 6.8 cm | 88.09 mm | 90 mm |
| 120/220, 6 x 9 | 5.6 cm x 8.2 cm | 99.30 mm | 105 mm |
| large format 4 x 5 sheet film | 10.16 cm x 12.7 cm (4" x 5") | 162.64 mm | 150 mm |
For a 35 mm camera with a diagonal of 43 mm, the most commonly used normal lens is 50 mm, but focal lengths between about 40 and 58 mm are also considered normal.
The 50 mm focal length was chosen by Oscar Barnack, the creator of the Leica camera, as a compromise between the theoretical value and good sharpness, as lens technology at the time was such that slightly longer focal lengths were able to achieve optimum sharpness.
In cinematography a focal length roughly equivalent to twice the diagonal of the image projected within the camera is considered normal.
See also: angle of view, photographic lens.pl:Obiektyw standardowy