Determine the focal length of a lens having an optical power D = -2dptr. What kind of lens is it?

The focal length is inversely proportional to the optical power of the lens, expressed in diopters: F = 1 / D.

A lens with negative power will be scattering. It will also have a focal length with a minus sign:

F = 1 / (-2 diopters) = 1 / (2 m-1) = -0.5 m.

Answer: Diffusion lens with focal length F = -0.5 m.

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