# f-number

### or f number

[ef-nuhm-ber]

- 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. Abbreviation: f/, f/, f, f:

Compare relative aperture.

## Origin of f-number^{}

First recorded in 1890–95

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# 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 apertureSee also T-number

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