Aperture
WordNet
noun
(1) An man-made opening; usually small
(2) A device that controls amount of light admitted
(3) A natural opening in something
WiktionaryText
Etymology
Latin < , pp. of , opposed to . See aperient.
Noun
- An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole; as, an aperture in a wall.
- An aperture between the mountains. --Gilpin.
- The back aperture of the nostrils. --Owen.
- Something which restricts the diameter of the light path through one plane in an optical system.
- The diameter of the aperture (in the sense above) which restricts the width of the light path through the whole system. For a telescope, this is the diameter of the objective lens. e.g. a telescope may have a 100 cm aperture.
Usage notes
The aperture of microscopes is often expressed in degrees, called also the angular aperture, which signifies the angular breadth of the pencil of light which the instrument transmits from the object or point viewed; as, a microscope of 100° aperture.