Purpose:Show spherical aberration in eye and its correction.
Description:Hand out to the students a piece of black construction paper with a pin. View a small lighted cross at a large distance from your eye with your glasses removed in a dark room. Because the room is dark, the iris of the eye will open wide, causing a large amount of spherical aberration. Then view the same lighted cross through the pinhole. Because the pinhole limits the useable aperture of the eye, spherical aberration is significantly reduced, and the cross appears clearer. This effect can be used to see distant objects more clearly if you suffer from nearsightedness