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
Something which restricts the diameter of the light path through one plane in an optical system
An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole; as, an aperture in a wall
The diameter of the exposed part of the object glass of a telescope or other optical instrument; as, a telescope of four-inch aperture
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 100cm aperture