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`Optical power
`
`From Wikipedia, the free encyclopedia
`
`For the power of light, see Radiant flux and Luminous flux.
`For magnifying power, see Magnification.
`Optical power (also referred to as dioptric power, refractive power, focusing power, or
`convergence power) is the degree to which a lens, mirror, or other optical system converges or
`diverges light. It is equal to the reciprocal of the focal length of the device: P = 1/f.[1] High optical
`power corresponds to short focal length. The SI unit for optical power is the inverse metre (m−1),
`which is commonly called the dioptre.
`Converging lenses have positive optical power, while diverging lenses have negative power. When a
`lens is immersed in a refractive medium, its optical power and focal length change.
`For two or more thin lenses close together, the optical power of the combined lenses is
`approximately equal to the sum of the optical powers of each lens: P = P1 + P2. Similarly, the optical
`power of a single lens is roughly equal to the sum of the powers of each surface. These
`approximations are commonly used in optometry.
`An eye that has too much or too little refractive power to focus light onto the retina has a refractive
`error. A myopic eye has too much power so light is focused in front of the retina. Conversely, a
`hyperopic eye has too little power so when the eye is relaxed, light is focused behind the retina. An
`eye with a refractive power in one meridian that is different from the refractive power of the other
`meridians has astigmatism. Anisometropia is the condition in which one eye has a different refractive
`power than the other eye.
`
`[edit]
`
`See also
`Vergence
`Lens clock
`Vertometer
`Lensmeter
`Plate scale
`References
`1. ^ Greivenkamp, John E. (2004). Field Guide to Geometrical Optics. SPIE Field Guides vol. FG01.
`SPIE. p. 7. ISBN 0-8194-5294-7.
`
`[edit]
`
`This optics-related article is a stub. You can help Wikipedia by expanding it.
`
`Categories: Optics Optics stubs
`
`This page was last modified on 26 February 2013 at 15:03.
`
`Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this
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