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The ratio of the focal length of a lens or lens system to the effective diameter of its aperture. Also called f-stop.

American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.



f number

(Photography) 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 and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˈɛfˌnʌm bər)

a number corresponding to the ratio of the focal length to the diameter of a lens system, esp. a camera lens. Symbol: f/
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.


n (Phot) → Blende f, → Blendenzahl f
Collins German Dictionary – Complete and Unabridged 7th Edition 2005. © William Collins Sons & Co. Ltd. 1980 © HarperCollins Publishers 1991, 1997, 1999, 2004, 2005, 2007
References in periodicals archive ?
The most fundamental combinatorial invariant of a simplicial poset P of rank d is its f-vector, which is denoted f (P) = ([f.sub.-1] (P), [f.sub.0] (P), [f.sub.1] (P), ..., [f.sub.d-1] (P)), and the f-numbers [f.sub.i](P) count the number of i-dimensional faces in P.
The h-numbers of P are defined as a certain integer transformation of its f-numbers, and knowing the f-numbers of P is equivalent to knowing its h-numbers.
"Ride-on trowels aid the contractor by helping them obtain much flatter floors with improved F-numbers (the measure of floor flatness)," he said.