A unit of measure of the power of a lens or mirror, equal to thereciprocal of itsfocal length in meters.Myopia is diagnosed and measured in diopters.
The dioptre adjustment mechanism of a pair of binoculars or of a camera viewfinder.
(photography,dated) A lens element attached to the front of a photographic lens to shorten the lens's minimum focus distance; also called a "close-up filter".
