f-number

or f number

[ ef-nuhm-ber ]

/ ˈɛfˌnʌm bər /

Save This Word!

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:

QUIZ

CAN YOU ANSWER THESE COMMON GRAMMAR DEBATES?

There are grammar debates that never die; and the ones highlighted in the questions in this quiz are sure to rile everyone up once again. Do you know how to answer the questions that cause some of the greatest grammar debates?

Question 1 of 7

Which sentence is correct?

His boss, whom he admires, is waiting to meet with him about the big project.

His boss, who he admires, is waiting to meet with him about the big project.

TAKE THE QUIZ TO FIND OUT

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, foamed metal

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