Looking Sharp The rod and cone cells in the central part of the retina--the fove

Question

Looking Sharp

The rod and cone cells in the central part of the retina--the fovea--are packed more closely, giving a more detailed view. This area of increased rod and cone density has a diameter of about 1.5mm. When you read a book, you want the image of the text you are reading to fall on the fovea. If you hold a book 30cm from your eyes, how wide is the spot on the page whose image just fills the fovea? That is, how wide an area do you see most clearly? Assume that the image on the retina forms 17mm from the lens in the eye (which gives 1/s' = 60). Explain.

Explanation / Answer

u = -30 cm
v = 17 mm
m = -v/u = 1.7/30 = 0.056
1.5/A = m
A = 26.470 cm in diameter

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