noun ·Rare ·Advanced level

Definitions

Noun

1. 1
   A unit of measure of the power of a lens or mirror, equal to the reciprocal of its focal length in meters. Myopia is diagnosed and measured in diopters.
2. 2
   a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists wordnet
3. 3
   The dioptre adjustment mechanism of a pair of binoculars or of a camera viewfinder.
4. 4
   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". dated
5. 5
   Any lens system, such as a telescope. obsolete

Show 4 more definitions

6. 6
   A theodolite or similar surveyor’s angle measuring device. obsolete
7. 7
   An alidade. obsolete
8. 8
   A surgical speculum. obsolete
9. 9
   An instrument for drawing the skull by projections. obsolete

Synonyms

All synonyms

alidadedioptre

Etymology

From Latin dioptra, from Ancient Greek διόπτρα (dióptra).

Related phrases

focal length

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.