The black cylinders shown here on the left contain photomultiplier tubes (PMT's) and their electromagnetic shielding. The adjacent boxes contain current to voltage converters and preamplifiers. The gain ,or light sensitivity, of the system is controlled by adjusting the voltage applied to the PMT's  in the range of 500 to 2000 Vdc. Also shown are filter wheels and associated stepper motors viewed edgewise. The rack mountable boxes on the right contain the custom circuitry for signal filtering  & amplification, PMT voltage adjustment and filter wheel indexing. The bottom box is a power supply and computer interface for commercial galvo laser scanners typically used in confocal and 2-photon microscopes.