ABSTRACT
The relationship between the concentration ratio and the angular field of view is a fundamental one that merits more than one demonstration. A primitive form of non-imaging concentrator, the light cone, has been used for many years. The flat absorber case occupies a special place because of its simplicity. Historically it was the first to be discovered. For these reasons its description and properties merit a separate discussion. It is a way of finding rays on the boundary between sets of rays that are turned back and rays that are transmitted. Cones are much easier to manufacture than Cones and Paraboloids as Concentrators. Paraboloids of revolution seem a more natural choice to conventional optical physicists than concentrators. The people shall therefore provide some quantitative comparisons. The section of a paraboloid of revolution in front of the focus is used for x-ray imaging, since most materials are good reflectors for x-rays at grazing incidence.
