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f-number

American  
[ef-nuhm-ber] / ˈɛfˌnʌm bər /
Or f number

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 British  

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

Etymology

Origin of f-number

First recorded in 1890–95

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.