Illumination control system for television pickup tubes and the like

Claim 1

IN A TELEVISION SYSTEM UTILIZING A SIGNAL PICKUP TUBE OF THE RETURN SCANNING BEAM TYPE HAVING A PHOTOCATHODE ONTO WHICH THE OPTICAL IMAGE OF THE SCENE BEING TELEVISED IS PROJECTED AND A SCANNING TARGET ON WHICH AN ELECTRICAL CHARGE IMAGE IS FORMED IN PROPORTIN TO THE INTENSITY OF PHOTOCATHODE ILLUMINATION BY PHOTOELECTRONS EMITTED FROM SAID PHOTOCATHODE, SAID TUBE ALSO HAVING VIDEO SIGNAL OUTPUT MEANS ENERGIZED BY THE ELECTRONS IN SAID RETURN BEAM; ELECTRICALLY-OPERATED MEANS FOR CONTROLLING THE INTENSITY OF LIGHT ADMITTED TO SAID PHOTOCATHODE INCLUDING A NULL TYPE REVERSIBLE ALTERNATING CURRENT SERVO MOTOR HAVING A CONTROL WINDING, MEANS FOR SENSING AN ELECTRICAL CURRENT INDEPENDENTLY OF THE VIDEO OUTPUT SIGNAL WHICH VARIES WITH VARIATIONS IN PHOTOCATHODE ILLUMINATION, A MODULATING DEVICE AND AMPLIFYING MEANS AND MEANS PRODUCING AN ALTERNATING CURRENT CARRIER SIGNAL CONNECTED TO SAID MODULATING DEVICE, MEANS FOR APPLYING THE SENSE CURRENT TO CONTROL SAID MODULATING AND AMPLIFYING MEANS TO PRODUCE AN AMPLIFIED MODULATOR SIGNAL, DEMODULATING MEANS CONNECTED TO RECEIVE SAID AMPLIFIED MODULATED SIGNAL INCLUDING MEANS PRODUCING A DIRECT CURRENT REFERENCE POTENTIAL WHICH IS COMPARED WITH THE DEMODULATED SIGNAL TO PRODUCE AN OUTPUT WHICH VARIES IN MAGNITUDE FROM SAID REFERENCE POTENTIAL WITH VARIATIONS IN PHOTOCATHODE ILLUMINATION, MEANS FOR CONVERTING THE DEMODULATED DIRECT CURRENT OUTPUT INTO AN ALTERNATING CURRENT, SAID CONVERTING MEANS OPERATING TO COMPARE THE DEMODULATED OUTPUT WITH A REFERENCE POTENTIAL AND PRODUCE AN ERROR SIGNAL PROPORTIONAL TO THE DIFFRENTIAL THEREBETWEEN, AND MEANS FOR AMPLIFYING THE ERROR SIGNAL AND APPLYING IT TO SAID CONTROL WINDING OF THE SERVO MOTOR TO DRIVE THE LATTER IN A NULL DIRECTION.

Claim 2

THE METHOD OF ATTENUATING THE EFFECT OF HIGH SCENIC ILLUMINATION IN A TELEVISION SYSTEM UTILIZING A TELEVISION PICKUP TUBE HAVING A PHOTOCATHODE AND A TARGET ON WHICH AN ELECTRICAL CHARGE IMAGE IS FORMED IN PROPORTION TO PHOTOCATHODE ILLUMINATION, WHICH COMPRISES GENERATING A PULSE WHICH VARIES IN WIDTH AS A FUNCTION OF PHOTOCATHODE ILLUMINATION, AND IMPRESSING SAID PULSE ON THE NORMAL PHOTOCATHODE SUPPLY POTENTIAL IN A MANNER SUCH AS TO INTERMITTENTLY VARY THE SAID SUPPLY POTENTIAL IN A DIRECTION TO REDUCE THE CHARGE ON THE TARGET.