Angular aperture
The angular aperture of a lens is the angular size of the lens aperture as seen from the focal point:
![](../I/m/Angular_aperture.svg.png)
The angular aperture of a thin lens with focal point at F and an aperture of diameter .
where
- is the focal length
- is the diameter of the aperture.
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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gollark: People running around with bits of paper.
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References
- Albert Abraham Michelson (1995). Studies in Optics. Courier Dover. p. 32. ISBN 0-486-68700-7.
See also
- f-number
- Numerical aperture
- Acceptance angle, half the angular aperture
- Field of view
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