Demo 22-02 Spherical Aberration in a Mirror

Using a large optical board, this demonstration illustrates the difference between a spherical and a parabolic mirror in focusing incoming parallel rays of light. Parallel rays focused in two dimensions by a circular surface exhibit spherical aberration; the outer rays are focused too close to the mirror, as seen in Figure 1. Substituting a parabolic mirror removes this aberration; a parabolic reflector is exactly the right shape to focus parallel rays to a point. In the video sets of rays at different distances from the central ray are made different colors to enhance visibility of the effect