How the optical power of the lens depends on the focal length

According to Bender’s law, the optical power of a lens is found through the expression 1 / F.

In this expression, F, in turn, is the focal length. It is measured in meters.

But the reality is not so simple.

And if we sum up all the observations, then we can come to the conclusion that this very formula is applicable only in certain cases. And in them, it is applicable only to a thin lens in air, as well as to the paraxial region of any lens in air.

The paraxial region is simply the central part of absolutely any lens.