Word.ws English Dictionary

dioptra

dioptra is the alternative form of diopter.

Meaning of diopter

Noun

diopter (plural diopters)

  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. The dioptre adjustment mechanism of a pair of binoculars or of a camera viewfinder.
  3. (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".
  4. (obsolete) Any lens system, such as a telescope.
  5. (obsolete) A theodolite or similar surveyor’s angle measuring device.
  6. (obsolete) An alidade.

See all 8 meanings of diopter

Questions about dioptra

What is dioptra the alternative form of?
Dioptra is the alternative form of diopter.

Words near dioptra in the dictionary

  1. dioptids
  2. dioptine
  3. dioptines
  4. dioptometer
  5. dioptometers
  6. dioptra
  7. dioptral
  8. dioptrate
  9. dioptre
  10. dioptres
  11. dioptric

Source and license

Adapted from Wiktionary: dioptra (page history and authors); diopter (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.

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Cite this entry: “dioptra.” Word.ws, https://word.ws/dioptra. Based on Wiktionary, CC BY-SA 4.0.