means for directing substantially collimated source supplied {TAIL ~ radiation} toward the second focusing reflector in {HEAD ~ the reflectance mode}; and 
means for directing substantially collimated source supplied { TAIL ~ radiation } toward the second focusing reflector in { HEAD ~ the reflectance mode } ; and
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH