Winston Cone -- from Eric Weisstein's World of Physics

A Winston cone is an off-axis parabola of revolution designed to maximize collection of incoming rays within some field of view (Winston 1970, Hildebrand and Winston 1982, Hildebrand 1985, Welford and Winston 1989). The above figure shows a schematic of a Winston cone. Winston cones are nonimaging light concentrators intended to funnel all wavelengths passing through the entrance aperture out through the exit aperture. They maximize the collection of incoming rays by allowing off-axis rays to make multiple bounces before passing out the exit aperture. Even so, there are certain families of off-axis rays which are rejected back out the entrance aperture. In addition, since diffraction effects become important for radiation wavelengths similar to the cone's physical dimensions, Winston cones exhibit a waveguide-like cutoff at low frequencies. In the above figure, the entrance and exit apertures are of radius a and , respectively. F is the focus of the upper parabola segments, and f is its focal length. The length of the cone is L. The diagram on the right shows the origins and orientations of the focus-centered and symmetry axis-centered coordinate systems.

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