Dictionary.com

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. Abbreviations:f/, f/, f, f:

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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

FMN, fMRI, FMS, fn, FNMA, f-number, Fo, foal, foam, foam at the mouth, foam cell
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

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 apertureSee also T-number
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012