Question

a person needs a lens of power minus 5.5 D for correcting his distance vision for correcting his near vision he needs power lens of + 1.5 D what is the focal length of lens required for correcting distant vision and their vision which type of lens is being used in correct and distant vision and near vision

Answer 1

In distant vision, power=-5.5D

So focal length= 1/-5.5

f = -0.18m= -18 cm

It means for myopic eye we use concave lens. Negative indicates concave.

In near vision, power=1.5D

So focal length= 1/1.5

f= 0.67m = +67 cm

It means for hypermetropic eye we use convex lens. Positive indicates convex.