an objective lens for focusing the electron beam emitted from said electron source upon {HEAD ~ the object} using {TAIL ~ an output} from the height detector 
an objective lens for focusing the electron beam emitted from said electron source upon { HEAD ~ the object } using { TAIL ~ an output } from the height detector
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH