f-number
f–num·ber
noun \ˈef-ˌnəm-bər\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
Origin of F-NUMBER
focal length
First Known Use: circa 1903
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