Control system for terminating the discharge of a flash lamp

Abstract

An arrangement for controlling the flash duration in photographic cameras. A light-sensitive element within the apparatus responds to light originating from the source for flash bulbs and reflected by the object or scene to be photographed. The flash bulb is ignited by an ignition circuit which also generates the operating voltage for the light-sensitive device. Through the application of a discharge tube which has a considerably lower internal resistance, when ignited, than the flash bulb, the latter becomes extinguished when the .Iadd.quantity of .Iaddend.light reflected by the object or scene and impinging upon the light-sensitive device, is .[.of.]. a predetermined .[.magnitude.]. .Iadd.quantity..Iaddend.

I claim: .[.1. An electronic flash arrangement for photographic cameras comprising, in combination, flash bulb means; ignition means connected to said flash bulb means for igniting said flash bulb means; light measuring means for responding to light from said flash bulb means and reflected by the object to be photographed; said ignition means connected to the light measuring means in a way as to deliver a D.C. operating voltage for the light measuring means, so that said D.C. operating voltage prevails only after the ignition of the flash bulb means, said flash bulb means becoming extinguished after ignition when the light reflected by said object and impinging upon said light measuring means is of a predetermined 
     
        magnitude..]. 2. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim .[.1.]. .Iadd.12 .Iaddend.wherein said ignition means comprises an ignition transformer connected to said flash .[.bulb.]. means; .[.and.]. .Iadd.an .Iaddend.ignition capacitor connected to said ignition transformer means; and a charging capacitor connected in series with said ignition capacitor and said ignition transformer means when said flash bulb means is ignited, the voltage across the charging capacitor resulting from .[.charging.]. .Iadd.discharge of .Iaddend.said ignition capacitor and being said .Iadd.D.C. .Iaddend.operating voltage 
     
     
        for operating said light measuring means. 3. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim .[.2.]. .Iadd.14 .Iaddend.wherein the capacitance of said charging capacitor is 
     
     
        large compared to the capacitance of said ignition capacitor. 4. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim 3 wherein the capacitance of said charging capacitor is ten times as 
     
     
        large as the capacitance of said ignition capacitor. 5. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim .[.1.]. .Iadd.12 .Iaddend.wherein said light measuring means includes the series connection of a light sensitive element, an adjustable resistor, 
     
     
        and an integrating capacitor. 6. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim 5 wherein said light sensitive 
     
     
        element is a photoresistor. 7. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim 5 including controlled silicon rectifying means with cathode-control electrode path connected to said integrating capacitor means, discharge tube means .Iadd.connected in .Iaddend.parallel with said flash bulb means and ignited by said controlled rectifier means, the internal resistance of said discharge tube means being substantially smaller when ignited than the resistance of said 
     
     
        flash bulb means. 8. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim 7 including protective resistor means between said integrating capacitor means and said .[.controlled.]..Iadd.control .Iaddend.electrode-cathode path of said 
     
     
        controlled rectifier means. 9. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim 7 including an ignition transformer connected to said discharge tube means for igniting the same; ignition capacitor means connected between said ignition transformer means and said controlled rectifier means; and voltage divider means connected 
     
     
        to said ignition capacitor means and said controlled rectifier means. 10. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim 9 including resistor means connected between said voltage divider means and the junction of said ignition capacitor means and said 
     
     
        controlled rectifier means. 11. The electronic flash arrangement .[.for photographic cameras.]. as defined in claim 10 wherein said resistor means has a resistance value .[.substantially of.]. .Iadd.in .Iaddend.the order of megohms. .Iadd. 12. An electronic flash arrangement for a photographic process, comprising in combination, flash generating means for generating a flash; ignition means connected to said flash generating means for igniting said flash generating means upon external activation, thereby initiating said flash, said external activation creating a current flow in said ignition means, said ignition means further comprising means for furnishing a D.C. voltage only after the start of said current flow; light measuring means operative only after application of an operating voltage thereto, for responding to light during an exposure and furnishing a terminating signal when said light has reached a predetermined light quantity; means connecting said ignition means to said light measuring means in such a manner that said D.C. voltage constitutes said operating voltage; and means connected to said light measuring means for terminating said flash upon receipt of said terminating signal. .Iaddend. .Iadd. 13. An electronic flash arrangement for a photographic process, comprising in combination, flash generating means for generating a flash; ignition means connected to said flash generating means for igniting said flash generating means upon external activation, thereby initiating said flash, said external activation creating a current flow in said ignition means, said ignition means further comprising means for creating a D.C. voltage only after the start of said current flow; light measuring means operative only after application of an operating voltage thereto, for responding to light during an exposure and furnishing a terminating signal when said light has reached a predetermined light quantity; means connecting said ignition means to said light measuring means in such a manner that said D.C. voltage constitutes said operating voltage; and means connected to said light measuring means for terminating said flash upon receipt of said terminating signal. .Iaddend. .Iadd. 14. An electronic flash arrangement for photographic process, comprising, in combination, flash generating means for generating a flash; ignition means connected to said flash generating means for igniting said flash generating means upon external activation, thereby initiating said flash, said ignition means comprising an ignition transformer connected to said flash generating means, an ignition capacitor connected to said ignition transformer and a charging capacitor connected to said ignition capacitor in response to said external activation in such a manner that a D.C. voltage is created across said charging capacitor resulting from discharge of said ignition capacitor; light measuring means operative only after application of an operating voltage thereto, for responding to light during an exposure and furnishing a terminating signal when said light has reached a predetermined light quantity; means for connecting said ignition means to said light measuring means in such a manner that said D.C. voltage across said charging capacitor constitutes said operating voltage; and means connected to said light measuring means and said flash generating means for terminating said flash upon receipt of said terminating signal..Iaddend.