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# What is the Optical Power of a Lens?

## Important Formula

## What do the formula symbols mean?

## Refractive power

`$$ D $$`Unit

`$$ \frac{1}{\mathrm m} $$`

The refractive power of a lens is the reciprocal of the focal length and is usually specified in

**dioptres**(\( \mathrm{dpt} ~=~ \frac{1}{\mathrm{m}} \)).## Focal length

`$$ f $$`Unit

`$$ \mathrm{m} $$`

Focal length is the distance between the lens and the focal point of the lens. The focal point is the point at which the lens focuses all light rays.

The **optical power** (formula symbol: \( D \)) indicates how strongly the light rays are refracted towards the focal point of a lens. The optical power is defined as the reciprocal of the focal length \( f \):

$$ \begin{align} D ~=~ \frac{1}{f} \end{align} $$

The unit of optical power is usually given in **diopters** (\( \mathrm{dpt} ~=~ \frac{1}{\mathrm{m}} \)).