Power (P): Converging or diverging capacity of a lens. The SI unit of power is dioptre (D), 1 dioptre is the power of a lens whose focal lens is 1 meter.
Formula for "power":
P= 1/fTechnic terms:
Look at these two convex mirrors below, which one has more power?
If you draw a imaginary line for each lens, you can see the first lens bent light ray more than the second one. So the first one has a higher power.
We can concluded: Greater the power, shorter the focal length.
The power of a diverging lens, in other word, a concave lens, is negative, because its focus lies on the negative side.