A lens is a piece of glass or other see-through material that is curved on one or both sides. When light passes through a lens it refracts or bends, making objects look bigger or smaller. When parallel laser beams are run through a convex lens they converge, and when they are run through a concave lens, they diverge (spread apart). An experiment for you to try: place a clear glass full of water beside a sunny window, wet the window with a warm water-soaked cloth and move a piece of white paper near the glass until you see a rainbow image. Or try a flashlight as your source of light.