The diopter is part of the viewfinding system of a camera that can be adjusted to compensate for your own particular eyesight, allowing you to see the groundglass clearly.
Glossary of Film Terms - http://homepage.newschool.edu/~schlemoj/film_courses/glossary_of_film_terms/ reprinted with permission
Unit of measurement, used to quantify the curvature of a lens. The strength of a lens measured in diopters is calculated:
strength = 1 / focal length where focal length is given in metres -- diopters have units of m-1.
where focal length is given in metres -- diopters have units of m-1.
Di*op"ter (?), Di*op"tra (?), n. [L. dioptra, fr. Gr. . See 2d Dioptric.]
An optical instrument, invented by Hipparchus, for taking altitudes, leveling, etc.
© Webster 1913.
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