For a thorough discussion both of the limitations of imaging S}@J4}*u["
optical systems in the collection of radiant energy and of the :gD=F &V
nonimaging collectors which can be used to collect energy }XJA#@
efficiently, see W.T. Welford and R. Winston, High Collection 3}:(.K
Nonimaging Optics, Academic Press (San Diego), 1989.