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PH 122 (46)

The eye, presbyopia, myopia, hyperopia

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Colorado State University
PH 122
Brian Jones

2 May Warming Up A camera is focused on an object at a distance of 1.0 m. Now, the object is moved closer, to a distance of 0.50 m. How must the position of the lens be changed to keep the image in focus? Move lens back, farther from object The Eye Most of the refraction occurs at the cornea’s surface, where Δn is the largest. Figuring the Near Point People in their early 20s have about 10 diopters of accommodation. For this range of accommodation, what is the near point? If s = ∞ 1 Far point: f = 60 1 70 = 60 + s s = 10 cm Presbyopia Farsightedness A woman who has never needed vision correction finds that, as she ages, her near point grows to 1.0 m – too distant for comfortable reading. Her distant vision is still quite good. If she would like to read at the more reasonable distance of 25 cm, what power lens does she need in a pair of reading glasses? What she has f.p. 60 1 1 n.p. = 60 + f s s = 1 m 61 What she wants 1 1 f = 60 + .25 = 64 What she needs Converging lens, +3 D What she gets – with this lens in place, what is her
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