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Additional
dioptre
English Wikipedia - The Free Encyclopedia
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Dioptre
A
dioptre
, or
diopter
, is a
unit of measurement
of the
optical power
of a
lens
or curved
mirror
, which is equal to the
reciprocal
of the
focal length
measured in
metres
(that is, 1/metres). It is thus a unit of
reciprocal length
. For example, a 3-dioptre lens brings parallel
rays
of light to focus at metre. The same unit is also sometimes used for other reciprocals of distance, particularly
radii of curvature
and the
vergence
of optical beams. The usage was proposed by French
ophthalmologist
Ferdinand Monoyer
in 1872, based on earlier use of the term
dioptrice
by
Johannes Kepler
.
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