f-number
/ˈefnʌmbə(r)/noun
- Photography the ratio of the focal length of a camera lens to the diameter of the aperture being used for a particular shot (e.g. f 8, indicating that the focal length is eight times the diameter)【摄】孔径焦距比, 光圈数, f 值。
词源
early 20th cent.: from f (denoting the focal length) and NUMBER.