This is done by controlling {HEAD ~ an adjustable optical filter} having {TAIL ~ an adjustable optical element} for each of the sampling positions 
having
This is done by controlling { HEAD ~ an adjustable optical filter } having { TAIL ~ an adjustable optical element } for each of the sampling positions
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH