The opening of a lens that admits light. Except in very simple cameras, the
Aperture can be varied in size by an adjustable diaphragm, which regulates the amount of light passing through the lens. The relative
Aperture is measured as the focal length of the lens divided by the diameter of the
Aperture; this is expressed as an f-number: f/3, f/5, and so on.
Aperature has a dramatic effect on the
Depth-of-field of the photograph.