How to convert focal length to diopters?


A lens of focal length f has the so called power \phi = \frac{1}{f}
As the focal length is given in mm, the power has the unit \frac{1}{mm}.

If the power is converted in units of \frac{1}{m} , one gets dopters.

A lens of 100mm focal length has a power of \phi = \frac{1}{f} =\frac{1}{100mm} = \frac{10}{1m} = 10 diopters