Angular aperture

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The angular aperture of a thin lens with focal point at F and an aperture of diameter .

The angular aperture of a lens is the angular size of the lens aperture as seen from the focal point:

where

is the focal length
is the diameter of the aperture.

Relation to numerical aperture[edit]

In a medium with an index of refraction close to 1, such as air, the angular aperture is approximately equal to twice the numerical aperture of the lens.[1]

Formally, the numerical aperture in air is:

In the paraxial approximation, with a small aperture, :

References[edit]

  1. ^ Albert Abraham Michelson (1995). Studies in Optics. Courier Dover. p. 32. ISBN 0-486-68700-7. 

See also[edit]