Classical optics was traditionally the mapping of point sources by lenses, mirrors and occasionally holograms , i.e.
making an image. The subject has had many famous scientists associated with it; Fermat, Huygens, Descartes,
Hamilton just to name a few. By the mid 20th Century it was a well-developed field as exemplified by such luminaries
as Walter T. Welford, Emil Wolf and many others. The theory of aberrations which addresses the imperfections of the
mapping codified the state of the art.
Then arose the need to collect energy, not just images. To the author’s knowledge it can be traced back to WWII
Germany with collection of infra-red radiation (the work by D. E. Williamson, was not published until 1952). The
radiation collector, a simple right-circular cone, was a harbinger of things to come.