## dioptreAlso known as a reciprocal meter, a unit used to express
the focal power of optical lenses. One dioptre
is the power of a lens that brings parallel light rays to a focus at a point
one meter from the lens, after passing through it. A stronger lens brings
light rays to a focus at a point closer to it than a weaker lens and has
a higher dioptric power. The power of a converging lens in dioptres is a positive number equal to the reciprocal of its focal length in meters. Diverging lenses have negative powers. For example, a diverging lens of focal length 1/3 meter has a power of 3 dioptres. The power of a combination of lenses is the sum of their individual powers. ## Related category• UNITS | |||||

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