The ripple tank is one of the physics education devices most appreciated by teachers and students. It allows one to visualize various phenomena related to wave physics in an effective and enthralling way. Usually this apparatus consists of a tank with a transparent bottom that is filled with a thin layer of water. A source of light illuminates the water surface from the top and the water is mechanically perturbed in order to produce regular waves. With the water crests and troughs acting as converging and diverging lenses, the surface configuration is reproduced on a screen using a play of light and shadows. We propose a simple and cheap change to this tool. Such a modification could be constructed by pupils themselves in their school laboratory. The lighting in our apparatus differs from the usual arrangement: the light is somewhat oblique with respect to the water surface, and a system of screens with holes and slits is placed at the bottom of the glass tank. This allows us to select and illuminate small portions of water. In this way our modified ripple tank gives us the possibility to perform new experiments and to explain by further examples the properties of waves.