diopter








noun

  1. Optics. a unit of measure of the refractive power of a lens, having the dimension of the reciprocal of length and a unit equal to the reciprocal of one meter. Abbreviation: D
  2. an instrument, invented by Hipparchus, to measure the apparent diameter of the sun or moon or to estimate the size or elevation of distant objects.

n.

  1. A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.
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