Film Term:

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.


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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