f-number

or f number

[ ef-nuhm-ber ]

/ ˈɛfˌnʌm bər /

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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

fMRI, FMS, FMV, fn, FNMA, f-number, Fo, foal, foam, foam at the mouth, foam cell

How to use f-number in a sentence

The program has not made a final selection on which upgrades will actually be included in future versions of the F-35.
Pentagon Misfires in Stealth Jet Scandal|Dave Majumdar|January 8, 2015|DAILY BEAST
That article noted that the F-35 does not currently have the ability to down-link live video to ground troops,.
Pentagon Misfires in Stealth Jet Scandal|Dave Majumdar|January 8, 2015|DAILY BEAST
In fact, according to F-35 program sources, the next software upgrades are not yet fully defined nor are they fully funded.
Pentagon Misfires in Stealth Jet Scandal|Dave Majumdar|January 8, 2015|DAILY BEAST
Therefore, it is not possible for any F-35 schedule to include a video data link or infrared pointer at this point.
Pentagon Misfires in Stealth Jet Scandal|Dave Majumdar|January 8, 2015|DAILY BEAST

“Our members continue to face a number of challenges,” she said.
The Republican War on Kale|Patricia Murphy|January 7, 2015|DAILY BEAST
The country is well inhabited, for it contains fifty-one cities, near a hundred walled towns, and a great number of villages.
Gulliver's Travels|Jonathan Swift
We had six field-pieces, but we only took four, harnessed wit twice the usual number of horses.
Blackwood's Edinburgh Magazine, No. CCCXXXIX. January, 1844. Vol. LV.|Various
There are a number of bacilli, called acid-fast bacilli, which stain in the same way as the tubercle bacillus.
A Manual of Clinical Diagnosis|James Campbell Todd
Five of the number had studied with Liszt before, and the young men are artists already before the public.
Music-Study in Germany|Amy Fay
E was an Esquire, with pride on his brow; F was a Farmer, and followed the plough.
Boys and Girls Bookshelf; a Practical Plan of Character Building, Volume I (of 17)|Various

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