The defective near point of an eye is 150 cm. Calculate the power of the correcting convex lens that would correct this defect of vision.

IN THIS QUESTION WHY SHOULD WE TAKE THE IMAGE DISTANCE AS= -150CM IF THE HYPERMETROPIC NEAR POINT IS JUST 150 CM....

The near point of an eye is also an object distance for the eye lens. All distances calculated opposite to the direction of incident rays are taken negative. While measuring this near point from the eye lens we measure it from the optical center of the eye to the near point (the direction of this measurement is opposite to the direction of incident light, since incident light is from the near point to the eye lens). So, the distance of the near point is taken as negative.

Hence, image distance, v = – 150 cm

We have the correction formula,

∴ Power of the correcting convex lens,

P =

Hence, a convex lens of power 3.3 D is required to correct the given defect of vision.