Explanation:

we use the formula 1/f = 1/v - 1/u for calculating both far point and near point

power is the reciprocal of focal length (1/f). focal length should be in metres.

Ex: A man cannot see objects closer than 1m from the eye. What is the power of the lens.

here v= -100cm, u= -25cm

1/f= -1/100 + 1/25 = 3/100cm

f=1/3m, power= +3diopters