対訳 F 値
出典:Wiktionary
出典:Wikipedia
出典:『Wikipedia』 (2011/07/12 00:39 UTC 版)
In optics, the f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture) of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter. It is a dimensionless number that is a quantitative measure of lens speed, an important concept in photography.