 Rather than CCDs these three instruments used photon-counting digicons as their detectors.  The FOC was constructed by ESA, while the University of California, San Diego and the Martin Marietta corporation built the FOS. 
 Rather than CCDs these three instruments used photon-counting digicons as their detectors.  The FOC was constructed by ESA, while the University of California, San Diego and the Martin Marietta corporation built the FOS. 