{HEAD ~ The central ray} of {TAIL ~ each composite illumination beam} is directed to be incident upon a separate preselected location on the subreflector 
{ HEAD ~ The central ray } of { TAIL ~ each composite illumination beam } is directed to be incident upon a separate preselected location on the subreflector
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH