My name is Alexander FufaeV and here I write about:
What is the Optical Power of a Lens?
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 \( f \):
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Definition of optical power
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Thin lens - object width, image width and focal length are shown.
The unit of optical power is usually given in diopters (\( \mathrm{dpt} ~=~ \frac{1}{\mathrm{m}} \)).
An average eye has approximately \( 22 \, \mathrm{dpt} \). So, when you hear something like: I have \( +2 \, \mathrm{dpt} \) at my left eye, you know that the focal length of their left eye is approximately \( f ~=~ \frac{1}{22 \, \mathrm{dpt} ~+~ 2 \, \mathrm{dpt}} ~\approx~ 41 \, \mathrm{mm} \). This person is farsighted!