1911 Encyclopædia Britannica/Aperture
|←Apenrade||1911 Encyclopædia Britannica, Volume 2
|See also Aperture on Wikipedia, and our 1911 Encyclopædia Britannica disclaimer.|
APERTURE (from Lat. aperire, to open), an opening. In optics, it is that portion of the diameter of an object-glass or mirror through which light can pass free from obstruction. It is equal to the actual diameter of the cylinder of rays admitted by a telescope.