f-Number
The f-number of an optical system, such as a camera lens, is the ratio of the system's focal length to the diameter of the entrance pupil. It is a quantitative measure of lens speed.
The f-number equals the focal length divided by the diameter of the aperture.
Formula
symbol | description | physical quantity |
---|---|---|
N | fnumber | "Unitless" |
D | diameter of aperture | "Diameter" |
f | focal length | "Length" |
Forms
Examples
Get the resource:
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Get the formula:
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Use some values:
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