The trough shaped reflectors are moved in {HEAD ~ synchronism} with {TAIL ~ the scanning movement} of the beams so that the images of the lamp filaments remain in one dimensional focus throughout scanning of the flat document plane 
with
The trough shaped reflectors are moved in { HEAD ~ synchronism } with { TAIL ~ the scanning movement } of the beams so that the images of the lamp filaments remain in one dimensional focus throughout scanning of the flat document plane
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH