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