Geometrical optics. when relaxed, the lens of the human eye focuses objects at infinity onto the retina. the effective lens-retina distance is approximately 1.7 cm, and thus the focal length of the relaxed eye is also 1.7 cm. the lens-retina distance (image distance) stays fixed as the eye focuses on near-by objects, but the focal length of the lens is changed (a) by how much does the focal length change when looking at an object 25 cm away (the near point, i. e. the closest distance at which your eye can view an object in focus)? (b) a farsighted person has their near-point > 25 cm, and needs glasses to see object: s clearly nearer at hand. suppose your near-point is 50 cm. if you try to read a book held 25 cm away from you, it will be out of focus because the image of the page is not on your retina. where is the image of the page? (c) design a corrective lens that will allow you to read a book held 25 cm away. (hint inverse focal lengths add when lenses are close