f number

f-number

, f number

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

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

f number

[′ef ‚nəm·bər]

(optics)

A lens rating obtained by dividing the lens's focal length by its effective maximum diameter; the larger the f number, the less exposure is given. Also known as focal ratio. Also known as stop number.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.