What is the focal length of the lenses in your eyes when you read a book that is 35cm

thanlong01 · #1 Oct 26, 2009, 05:59 PM

What is the focal length of the lenses in your eyes when you read a book that is 35cm from them? The Distance from each lens to the retina is 0.19mm

harum · Oct 31, 2009, 10:54 AM

Do you mean the book is 35 cm away from your eyes? If yes, then use that "thin lens" formula and remember that eye has a biconvex lens: 1/f + 1/d = 1/F. Here, d - distance to the book from the lens, f - distance to the retina from the lens. and F - eye's lens focal length. Solve for F the above equation. You assume here that eyes adjust the focal distance, so that you see the book image sharply at retina.



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