Difference between revisions of "Aperture Ratio"
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Aperture Ratio
The ratio of the useful diameter of a lens to its focal length.
It is the reciprocal of the f-number.
In application to
an optical instrument, rather than to a lens, numerical aperture
is more commonly used. The aperture ratio is then twice the tangent
of the angle whose sine is the numerical aperture.
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use