Angular aperture
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The angular aperture of a lens is the apparent angle of the lens aperture as seen from the focal point:
where
- f is the focal length
- d is the diameter of the aperture.
[edit] Relation to numerical aperture
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, D < f:
[edit] References
- ^ Albert Abraham Michelson (1995). Studies in Optics. Courier Dover, 32. ISBN 0486687007.
