The optical power of the lens is 0.4 diopters. Determine the focal length of the lens?

Given:

D = 0.4 diopters.

To find:

F -?.

Let’s recall the definition of the optical power of a lens.

Optical power is a value that characterizes the refractive power of axisymmetric lenses and centered optical systems made of such lenses.

The unit of measurement for this value is the diopter (symbol: diopters): 1 diopters = 1 m – 1.

The optical power of a lens is the reciprocal of its focal length. Let’s write this in the form of a formula:

D = 1 / F;

Let us express from the formula F:

F = 1 / D.

Substitute the values and calculate:

F = 1 / 0.4 = 2.5 m.