Generating, at each vignetted light sensor, {HEAD ~ a measurable electrical quantity} responsive to {TAIL ~ the associated vignetted light field}, 
responsive to
Generating , at each vignetted light sensor , { HEAD ~ a measurable electrical quantity } responsive to { TAIL ~ the associated vignetted light field } ,
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH