f-number

or f number

[ ef-nuhm-ber ]

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

Origin of f-number

1
First recorded in 1890–95
  • Also called f value, focal ratio, speed, stop number .

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

British Dictionary definitions for f-number

f-number

noun
  1. 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

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