The beam splitter 30 may split {TAIL ~ the image beam} C into a first projecting beam C1 and {HEAD ~ a second projecting beam} C2 
The beam splitter 30 may split { TAIL ~ the image beam } C into a first projecting beam C1 and { HEAD ~ a second projecting beam } C2
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH