We have been experimenting with programs for ray tracing as a way of visualizing how the energy is distributed in solar cookers. Ther first program was for a parabolic cooker. The program was written in MathCad and the animation that was generated by the program is available below. You can play the video or by moving the slider you can experiment with different sun angles. Notice how the focal point becomes a focal area that gets larger as the sun moves away from the axis of the parabola.