f-num·​ber ˈef-ˌnəm-bər How to pronounce f-number (audio)
: the ratio of the focal length to the aperture in an optical system
: a number following the symbol f/ that expresses the effectiveness of the aperture of a camera lens in relation to brightness of image so that the smaller the number the brighter the image and therefore the shorter the exposure required

Word History


focal length

First Known Use

1898, in the meaning defined at sense 1

Time Traveler
The first known use of f-number was in 1898

Dictionary Entries Near f-number

Cite this Entry

“F-number.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/f-number. Accessed 19 Jul. 2024.

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