| 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. |