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

<math>a = 2 \arctan \frac {A} {2 f}</math>

where

<math>f</math> is the focal length

<math>A</math> is the diameter of the aperture.

The angular aperture is approximately equal to twice the numerical aperture of the lens.

[edit] See also

• f-number
• Numerical aperturees:Apertura angular