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Perspective
Angular aperture
From Wikipedia, the free encyclopedia
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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.
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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, :
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References
See also
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