# Optical power of a lens

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Optical power of a lens is a quantity that is inversely proportional to the focal length; therefore, it can be calculated in diopters.

It is denoted by the letter D, and the unit of optical power is the diopter. 1 diopter is the optical power with a focal length of 1 meter.

In the SI system, the unit of measurement for optical power is the inverse meter.

[dpt] = [1/m] = [m⁻¹]

Lenses that converge and diverge differ in their primary functions. This means that their optical powers will differ. For converging lenses, a positive sign is used before the optical power, while for diverging lenses, a negative sign is used.

If you need to calculate the optical power of a system consisting of two lenses, you can use the formula:

D = D1 + D2 – dD1D2,

Where:

D – the final optical power,

D1 – the optical power of the first lens,

D2 – the optical power of the second lens,

d – the distance between the lenses.

For a system of thin lenses, the power is calculated as the algebraic sum of the optical powers of each lens:

D = D1 + D2 + D3 + … + Dn.