f-number

or f number

[ ef-nuhm-ber ]
/ ˈɛfˌnʌm bər /

noun Optics, Photography.

a number corresponding to the ratio of the focal length to the diameter of a lens system, especially a camera lens. In f/1.4, 1.4 is the f-number and signifies that the focal length of the lens is 1.4 times as great as the diameter. Abbreviation: f/, f/, f, f:
Also called f value, focal ratio, speed, stop number.
Compare relative aperture.

Origin of f-number

First recorded in 1890–95

Words nearby f-number

f, f, f-, f-bomb, f-factor, f-hole, f-number, f-stop, f-system, f-word, f., f. & t.

British Dictionary definitions for f-number

f-number

f number

noun

photog the numerical value of the relative aperture. If the relative aperture is f8, 8 is the f-number and indicates that the focal length of the lens is 8 times the size of the lens aperture See also T-number