The optical power of the lens is equal to – 1.6 diopters. What is the focal length of this lens?

The optical power of the lens is equal to – 1.6 diopters. What is the focal length of this lens? Can you get a valid image with it? What is the focus of a lens (give a precise definition)?

Given:
D = -1.6dptr
Find: F-?
Decision:
D = 1 / F
F = 1 / D = 1 / -1.6 = -0.625m
Answer: the focal length of the lens is -0.625m, it cannot get a real image.
The focus of a lens is the point located on the main optical axis of the lens at which all rays that fall on the lens parallel to the main optical axis intersect. Each lens has two focuses. A trick can be imaginary and real. The actual focus is formed by the rays refracted in the lens, and the imaginary focus is formed by the extensions of the rays that have passed through the lens.