User talk:Fred Rasio

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Regarding this edit to Photographic lens, note that despite the conventional wisdom among photographers, the f-number is not always equal to the ratio of the focal length to the diameter of the physical aperture inside the lens. The two are always proportional for any given lens, but the constant of proportionality depends on the lens design. What is true, though, is that the f-number is equal to the ratio of the focal length to the diameter of the lens' entrance pupil, which is sort of the "effective aperture" of the lens. --Srleffler 07:43, 25 April 2006 (UTC)