Compensating system for photocells of exposure control apparatus for making color prints

Claim 1

A COMPENSATING SYSTEM OPERABLE TO COMPENSATE FOR THE UNDESIRABLE CHARACTERISTICS OF PHOTOELECTRIC CELLS IN A COLOR BALANCING BRIDGE CIRCUIT FOR DETERMINING THE RATIO OF LIGHT OF THE PRIMARY COLORS IN THE LIGHT BEAM EMERGING FROM A PHOTOGRAPHIC PRINTER AND ENLARGER COMPRISING: (A) A SOURCE OF ELECTRICAL ENERGY OF HIGH AND LOW VOLTAGE MAGNITUDE, (B) A PLURALITY OF PHOTOELECTRIC CELLS RESPECTIVELY RESPONSIVE TO THE DISTRIBUTION OF THE PRIMARY COLORS OF GREEN, RED AND BLUE PRESENT IN THE LIGHT BEAM IMPINGING THEREON WITH THE IMPEDANCE OF EACH SAID PHOTOELECTRIC CELL BEING VARIABLE IN ACCORDANCE WITH THE INTENSITY OF THE PARTICULAR PRIMARY COLOR TO WHICH IT IS RESPONSIVE, (C) VOLTAGE REGULATING MEANS COMPRISING A TRANSISTOR CONNECTED TO SAID SOURCE OF HIGH-VOLTAGE MAGNITUDE THROUGH A LOAD RESISTOR AND HAVING AN EMITTER-COLLECTOR CIRCUIT INCLUDING EACH OF SAID PHOTOELECTRIC CELLS AND AN INDIVIDUAL SERIES CONNECTED LOAD RESISTOR THEREFOR TO PRODUCE A REFERENCE VOLTAGE ACROSS EACH PHOTOELECTRIC CELL CORRESPONDING TO APPROXIMATELY ONE-HALF THAT OF SAID SOURCE OF LOW-VOLTAGE MAGNITUDE,