f-number

or f number

[ ef-nuhm-ber ]

noun

, Optics, Photography.

1. 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. : f /, f/, f, f:

f-number

noun

1. See T-number
   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

Word History and Origins

Origin of f-number¹

First recorded in 1890–95