Question

A farsighted person has a near point of 75 cm rather the normal 25 cm. What strength lens, in diopters, should be prescribed to correct this vision problem?
Object , o = 25cm, image, i= -75cm(negative, in front of lens)

Martin is severe myopia, with a far point of 15cm. he wants to get a glass that he ‘ll wear while using his computer, whose screen is 75cm away. What refractive power will these glasses required? Object, o=75 cm, image, i=-15cm.

Answer 1

1 / f = 1 / 25 + ( 1 / 75 )

1 / f = 0.04 - 0.0133

1 / f = 0.0267

f = 1 / 0.0267

f = 37.45 cm

or

f = 0.3745 m

strength = 1 / f

= 1 / 0.3745

= 2.67 diapters

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1 / f = 1 / 75 - 1 / 15

1 / f = 0.0133 - 0.066

1 / f = - 0.0527

f = - 1 / 0.0527

f = - 18.97 cm

or

f = - 0.1897 m

the refractive power is

= 1 / f

= - 1 / 0.1897

= - 5.27 diapters