(c) Suppose the eye is farsighted; the person cannot clearly see objects that are closer than 1.0 m. Find the contact lens power you would prescribe so that objects as close as 20.0 cm can be seen clearly.
Answer 1
Using the thin lens equation 1/obj. dist. + 1/img. dist. = 1/fl
Uncorrected: 1/d(unc) + 1/0.017 = 1/f(lentils)
Fixed: 1/d(corr) + 1/0.017 = 1/f(goals) + 1/f(goal correct)
So 1/f(lens corr) = 1/d(corr) – 1/d(unc)
1/f(corr. lens) = 1/0.2 – 1/1 = +4 diopters.
Note that the lens-retina distance comes out of the calculations.