Question

The far point of a myopic person is 150 cm in front of the eye. What should be the nature and power of the corrective lens used to restore proper vision?

Answer 1

Distance of far point x = 150 cm = 1.5 m

To view distant objects concave lens of focal length of -1.5 m should be used.

i.e. -f = -x = -1.5 m

Power of lens = 1/f = 1/(-1.5) = -0.67 D

Answer 2

1/f= 1/v - 1/u

1/f = (1/-150) - (1/infinity)

P = 1/f = -100/150

= -0.67 D