ABSTRACT

In this chapter, the authors examine image-forming concentrators of conventional form—paraboloidal mirrors, lenses of short focal length, and so forth—and estimate their performance. They also examine the performance of mirror systems as concentrators. However, little seems to have been published in the way of angle transmission curves for such systems. It must be quite clear by now that, whatever the theoretical possibilities, practical concentrators based on classical image-forming designs fall a long way short of the ideal. As to theoretical possibilities, it is certainly possible to have an ideal concentrator of theoretical maximum concentration ratio if the people use a spherically symmetric geometry, a continuously varying refractive index, and quite unrealistic material properties. Nevertheless, imaging and non-imaging are not opposite concepts. Vignetting is caused by rims of components at either end of a long system shearing against each other as the system is turned off-axis.