A measure of the light-collecting power of a lens, telescope, etc., which is usually expressed in terms of its f-number (a lower f-number corresponding to a larger aperture), and is used in determining the exposure needed.
Origin
Late 19th century.
Definition of relative aperture in US English:
relative aperture
noun
Optics Photography
A measure of the light-collecting power of a lens, telescope, etc., which is usually expressed in terms of its f-number (a lower f-number corresponding to a larger aperture), and is used in determining the exposure needed.