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