# Problem: A farsighted person has a near point of 72 cm rather than the normal 25 cm. What strength lens, in diopters, should be prescribed to correct this vision problem?

###### FREE Expert Solution

Lens equation:

$\overline{)\frac{\mathbf{1}}{{\mathbit{s}}_{\mathbit{o}}}{\mathbf{+}}\frac{\mathbf{1}}{{\mathbit{s}}_{\mathbit{i}}}{\mathbf{=}}\frac{\mathbf{1}}{\mathbit{f}}}$

Power of a lens:

$\overline{){\mathbf{D}}{\mathbf{=}}\frac{\mathbf{1}}{\mathbf{f}}}$

1 diopter = 1 m-1

The lens has to create an image that appears to be at the near point of the person's uncorrected vision:

si = -72 cm

###### Problem Details

A farsighted person has a near point of 72 cm rather than the normal 25 cm. What strength lens, in diopters, should be prescribed to correct this vision problem?