Optical power
Measure of a lens's ability to converge or diverge light.
Optical power, also known as dioptric power, refractive power, focal power, focusing power, or convergence power, is a measure of the degree to which a lens, mirror, or other optical system converges or diverges light. It is defined as the reciprocal of the focal length, with high optical power corresponding to a short focal length. The SI unit for optical power is the inverse metre (m⁻¹), commonly called the dioptre (symbol: dpt or D).
- field
- Optics
- SI unit
- inverse metre (m⁻¹), also called dioptre (dpt or D)
- formula
- P = 1/f
- converging lenses
- positive optical power
- diverging lenses
- negative optical power
- combined thin lenses
- P ≈ P₁ + P₂
Lore & Background
Optical power is a fundamental concept in optics, describing how strongly a lens or mirror bends light. 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 placed close together, the combined optical power is approximately the sum of the individual powers, a principle commonly used in optometry.
Reader's Guide
Optical power is central to understanding vision correction. An eye with too much refractive power is myopic, focusing light in front of the retina and noted as a minus power. An eye with too little power is hyperopic, focusing light behind the retina when relaxed. Astigmatism occurs when refractive power differs between meridians, also called cylindrical power. Anisometropia is the condition where one eye has a different refractive power than the other. These concepts rely directly on the definition of optical power as the reciprocal of focal length.
Did You Know?
- Optical power is equal to the reciprocal of the focal length of the device.
- Converging lenses have positive optical power, while diverging lenses have negative power.
- For two or more thin lenses close together, the combined optical power is approximately the sum of the individual powers.
- A myopic eye has too much power, focusing light in front of the retina, noted as a minus power.
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