f-number

noun
f-num·​ber | \ ˈef-ˌnəm-bər How to pronounce f-number (audio) \

Definition of f-number

1 : the ratio of the focal length to the aperture in an optical system
2 : 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

First Known Use of f-number

1898, in the meaning defined at sense 1

History and Etymology for f-number

focal length

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Time Traveler for f-number

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The first known use of f-number was in 1898

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Dictionary Entries near f-number

fndg

fndn

fndr

f-number

fo

FO

Fo

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Statistics for f-number

Cite this Entry

“F-number.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/f-number. Accessed 26 Oct. 2020.

More from Merriam-Webster on f-number

Britannica.com: Encyclopedia article about f-number

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