Photographic printing apparatus

Claim 1

A PHOTOGRAHPIC PRINTING APPARATUS, COMPRISING A CATHODE RAY TUBE, A MEANS COUPLED TO SAID CATHODE RAY TUBE FOR FOCUSING AN ELECTRON BEAM ON THE FLUORESCENT SURFACE OF SAID CATHODE RAY TUBE TO PRODUCE A LIGHT SPOT ON SAID SURFACE, A SCANNING MEANS WHICH PRODUCES AT LEAST TWO DEFLECTING ELECTRIC SIGNALS EACH HAVING A SYMMETRICAL TRIANGULAR FORM AND HAVING FREQUENCIES WHICH ARE SLIGHTLY DIFFERENT FROM EACH OTHER, SAID SCANNING MEANS BEING COUPLED TO SAID CATHODE RAY TUBE FOR MAKING SAID LIGHT SPOT SCAN AN ORIGINAL NEGATIVE DISPOSED IN FRONT OF THE FLUORESCENT SURFACE SO THAT THE DENSITY VARIATIONS OF THE ORIGINAL NEGATIVE ARE CONVERTED TO TIME DIFFERENTIATED INTENSITY VARIATIONS, A MEANS IN THE PATH OF SAID LIGHT WITH THE TIME DIFFERENTIAL INTENSITY VARIATIONS THEREIN FOR PROJECTING A PART OF SAID LIGHT FROM SAID PATH, A PHOTOSENSITIVE TUBE INTO WHICH SAID PART OF SAID LIGHT IS PROJECTED AND WHICH PRODUCES A CONTINUOUS ELECTRIC SIGNAL, A LOW PASS FILTER HAVING MEANS FOR VARYING THE CHARACTERISTICS THEREOF AND TO WHICH SAID PHOTOSENSITIVE TUBE IS CONNECTED TO SUPPLY THE OUTPUT SIGNAL OF SAID TUBE TO SAID FILTER, AN AMPLIFYING MEANS CONNECTED TO SAID FILTER FOR AMPLIFYING THE OUTPUT OF SAID LOW PASS FILTER, AN INTENSITY MODULATING MEANS COUPLED TO SAID CATHODE RAY TUBE FOR IMPARTING AN INTENSITY MODULATION TO SAID CATHODE RAY TUBE AND TO WHICH INTENSITY MODULATION MEANS SAID AMPLIFIER IS CONNECTED TO FEED THERETO THE NEGATIVE POLARITY OF THE AMPLIFIED OUTPUT OF SAID AMPLIFYING MEANS, WHEREBY A CLOSED NEGATIVE FEEDBACK CIRCUIT IS FORMED, AND FOCUSING MEANS IN THE PATH OF SAID LIGHT FOR FOCUSING THE REMAINDER OF SAID LIGHT PASSED THROUGH THE ORIGINAL NEGATIVE ONTO A PIECE OF PHOTOGRAPHIC PAPER.