Parabolic mirror reflecting 3 parallel light beams to the focal point of the mirror. The 3 primary colours, red, green and blue when combined additively produce a spot of white light. Isaac Newton used a parabolic mirror for his reflecting telescope, a landmark in the history of telescopes and the prototype for a design that later came to be called a newtonian telescope. A mirror that is flatter thean the one shown here will bring the beams to a focus further away from the mirror. The reflections from the mirror are called caustic reflections. In optics, a caustic or caustic network is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface.