The angular aperture of a lens is the angular size of the lens aperture as seen from the focal point:
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/Angular_aperture.svg/250px-Angular_aperture.svg.png)
where
- is the focal length
- is the diameter of the aperture.
Relation to numerical aperture
editIn 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- ^ Albert Abraham Michelson (1995). Studies in Optics. Courier Dover. p. 32. ISBN 0-486-68700-7.
See also
edit- f-number
- Numerical aperture
- Acceptance angle, half the angular aperture
- Field of view