to determine what focal length is normal for a given format, simply calculate the diagonal of the format frame.
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the nikon d90's sensor is 23.6x15.8 mm. use the pythagorean theorem. sqrt((23.6^2)+(15.8^2)) = 28.4007. the diagonal of that rectangle is 28.4007 mm. therefore, a lens with a focal length of 28.4 mm is normal on the nikon d90.
consider the medium format (120- or 220-film) 6x6 cm frame. sqrt(2*(60^2)) = 84.8528. therefore, a lens with a focal length of 84.85 mm is normal on a 6x6 cm frame.
135-film is typically 24x36 mm per frame. sqrt((24^2)+(36^2)) = 43.2666. therefore, a lens with a focal length of 43.27 mm is normal on a 24x36 mm frame.
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fun fact: the advertised focal length of a given lens is often a few millimeters off. see this page for some examples (others can readily be found via google). he finds that his 500 mm lens is 500.1 mm, his 300 mm is 295.76 mm, and his 135 mm is 132.39 mm. i would guess that it varies from lens to lens.
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another exciting photography-related thread for asemi!
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the nikon d90's sensor is 23.6x15.8 mm. use the pythagorean theorem. sqrt((23.6^2)+(15.8^2)) = 28.4007. the diagonal of that rectangle is 28.4007 mm. therefore, a lens with a focal length of 28.4 mm is normal on the nikon d90.
consider the medium format (120- or 220-film) 6x6 cm frame. sqrt(2*(60^2)) = 84.8528. therefore, a lens with a focal length of 84.85 mm is normal on a 6x6 cm frame.
135-film is typically 24x36 mm per frame. sqrt((24^2)+(36^2)) = 43.2666. therefore, a lens with a focal length of 43.27 mm is normal on a 24x36 mm frame.
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fun fact: the advertised focal length of a given lens is often a few millimeters off. see this page for some examples (others can readily be found via google). he finds that his 500 mm lens is 500.1 mm, his 300 mm is 295.76 mm, and his 135 mm is 132.39 mm. i would guess that it varies from lens to lens.
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another exciting photography-related thread for asemi!
appreciated this thread two years later.
nice! :)