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In optics, 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 (symbol: dpt).

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: $P = P 1 + P 2$ . 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. This is noted as a minus power. 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. This is also known as a cylindrical power. Anisometropia is the condition in which one eye has a different refractive power than the other eye.

References

^ Greivenkamp, John E. (2004). Field Guide to Geometrical Optics. SPIE Field Guides vol. FG01. SPIE. p. 7. ISBN 0-8194-5294-7.

[1] Greivenkamp, John E. (2004). Field Guide to Geometrical Optics. SPIE Field Guides vol. FG01. SPIE. p. 7. ISBN 0-8194-5294-7.

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+{{short description|Degree to which an optical system converges or diverges light}}
-{{For|the power of light|Radiant flux|Luminous flux}}
-{{For|magnifying power|Magnification}}
+{{About||magnifying power|Magnification|the power of light|Radiant flux|and|Luminous flux}}
+[[File:optical_power_of_a_lens.svg|thumb|Illustration of the relationship between optical power in diopters and focal length in meters.]]
-'''Optical power''' (also referred to as '''dioptric power''', '''refractive power''', '''focusing power''', or '''convergence power''') is the degree to which a [[lens (optics)|lens]], [[mirror]], or other optical system converges or diverges light. It is equal to the [[Multiplicative inverse|reciprocal]] of the [[focal length]] of the device.<ref>{{cite book | first=John E. | last=Greivenkamp | year=2004 | title=Field Guide to Geometrical Optics | publisher=SPIE | others=SPIE Field Guides vol. '''FG01''' | isbn=0-8194-5294-7 |page=7 }}</ref> The [[dioptre]] is the most common unit of measurement of optical power. The SI unit for optical power is the [[inverse metre]] (m<sup>−1</sup>).
+In [[optics]], '''optical power''' (also referred to as '''dioptric power''', '''refractive power''', '''focusing power''', or '''convergence power''') is the degree to which a [[lens (optics)|lens]], [[mirror]], or other optical system converges or diverges light. It is equal to the [[Multiplicative inverse|reciprocal]] of the [[focal length]] of the device: {{math|{{nowrap|1=''P'' = 1/''f''}}}}.<ref>{{cite book | first=John E. | last=Greivenkamp | year=2004 | title=Field Guide to Geometrical Optics | publisher=SPIE | others=SPIE Field Guides vol. '''FG01''' | isbn=0-8194-5294-7 |page=7 }}</ref> High optical power corresponds to short focal length. The SI unit for optical power is the [[inverse metre]] (m<sup>−1</sup>), which is commonly called the ''[[dioptre]]'' (symbol: dpt).
-For two or more [[thin lens]]es close together, the optical power of the combined lenses is approximately equal to the sum of the optical powers of each lens. Similarly, the optical power of a single lens is roughly equal :P to the sum of the powers of each surface. These approximations are commonly used in [[optometry]].
-When a lens is immersed in a [[medium (optics)|refractive medium]], its optical power and focal length change.<!--A description of how they change, with reference to a reliable source, would be useful here.-->
+[[Converging lens]]es have positive optical power, while [[diverging lens]]es have negative power. When a lens is immersed in a [[medium (optics)|refractive medium]], its optical power and focal length change.<!--A description of how they change, with reference to a reliable source, would be useful here.-->
+For two or more [[thin lens]]es close together, the optical power of the combined lenses is approximately equal to the sum of the optical powers of each lens: {{math|{{nowrap|1=''P''&nbsp;=&nbsp;''P''<sub>1</sub>&nbsp;+&nbsp;''P''<sub>2</sub>}}}}. 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 [[human eye|eye]] that has too much or too little refractive power to [[focus (optics)|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 (perimetry, visual field)|meridian]] that is different from the refractive power of the other meridians has [[Astigmatism (eye)|astigmatism]]. [[Anisometropia]] is the condition in which one eye has a different refractive power than the other eye.
+An [[eye]] that has too much or too little refractive power to [[focus (optics)|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. This is noted as a minus power.  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 (perimetry, visual field)|meridian]] that is different from the refractive power of the other meridians has [[Astigmatism (eye)|astigmatism]]. This is also known as a cylindrical power.  [[Anisometropia]] is the condition in which one eye has a different refractive power than the other eye.
 ==See also==
+*[[Accommodation of the eye]]
-*[[Vergence (optics)|Vergence]]
 *[[Lens clock]]
-*[[Vertometer]]
 *[[Lensmeter]]
 *[[Plate scale]]
+*[[Vergence (optics)|Vergence]]
+*[[Vertometer]]
 ==References==
+{{Reflist}}
-<references/>
-[[Category:Optics|Power]]
+{{Authority control}}
-{{optics-stub}}
+[[Category:Optical quantities|Power]]
-[[ca:Potència òptica]]
-[[cs:Optická mohutnost]]
-[[es:Potencia (Óptica)]]
-[[fr:Puissance optique]]
-[[id:Daya optis]]
-[[kk:Линзаның оптикалық күші]]
-[[mk:Оптичка моќ]]
-[[ja:屈折力]]
-[[pl:Zdolność skupiająca]]
-[[ru:Оптическая сила]]
-[[sk:Optická mohutnosť]]
-[[uk:Оптична сила]]
-[[zh:光學倍率]]