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

QuantityVariable["N", "Unitless"] == QuantityVariable["f", "Length"]/QuantityVariable["D", "Diameter"]

symbol	description	physical quantity
N	fnumber	"Unitless"
D	diameter of aperture	"Diameter"
f	focal length	"Length"

Forms

Examples

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External Links

http://en.wikipedia.org/wiki/F-number

Source Metadata

Contributor:
Date: 1867