The main optical housing 56 includes a viewing aperture 68 serving as {HEAD ~ an entrance pupil region} to enable {TAIL ~ light} from the object being viewed to pass into the reflecting assemblies of the optical system 
to enable
The main optical housing 56 includes a viewing aperture 68 serving as { HEAD ~ an entrance pupil region } to enable { TAIL ~ light } from the object being viewed to pass into the reflecting assemblies of the optical system
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH