Electronic flash apparatus

Claim 2

Electronic flash apparatus comprising a flash tube for emitting photographic light during discharge of the tube, means for interrupting discharge of said tube to stop emission of light therefrom, and integrating means for integrating light reflected from a subject to be photographed and for providing a signal impulse to said interrupting means when the integrated reflected light reaches a desired value, said integrating means including a photosensitive control member 9, 17 having a control grid and a cathode, said integrating means also including circuit means so arranged that the cathode potential of said photosensitive control member is reduced in accordance with the time change in the voltage prevailing in the control grid, and so that said circuit means emits said signal impulse as soon as said cathode potential falls below said control grid potential, which has been reduced to the extent of the ignition voltage, said circuit means including a voltage divider having two resistors 15, 16 one of which (16) is variable in accordance with the time change of the voltage prevailing in the control grid of the photosensitive control member, and wherein the cathode potential of the photosensitive control member is determined by said voltage divider.

Claim 3

Apparatus as defined in claim 1, wherein said circuit means includes a transistor 14 having a collector-emitter circuit in parallel with said variable resistor 16, the base-emitter voltage of said transistor 14 corresponding to the time change of the voltage prevailing in the control grid of the photosensitive control member.

Claim 4

Apparatus as defined in claim 2, wherein said circuit means includes an integrating capacitor 10 connected to said photosensitive control member, and said circuit means also includes a series circuit parallel to said capacitor 10, said series circuit including the base-emitter section of said transistor 14 and an RC member composed of a resistor 11 and a capacitor 12.

Claim 5

Apparatus as defined in claim 3, wherein said photosensitive control member comprises a photo-transistor 9 and a thyristor 17, the control grid of the thyristor 17 being connected to the emitter of the photo-transistor 9 and to said integrating capacitor 10.

Claim 6

Electronic flash apparatus comprising a flash tube for emitting photographic light during discharge of the tube, means for interrupting discharge of said tube to stop emission of light therefrom, and control means for controlling operation of said interrupting means, said control means including a photosensitive member responsive to light reflected from a subject being photographed, an integration capacitor charged through said photosensitive member, a thyristor having an anode, a cathode, and a control grid, said thyristor being effective when it becomes conductive in its anode-cathode path to initiate operation of said interrupting means, means connected to said photosensitive member and to the grid of said thyristor for supplying said grid with an increasing potential depending on the integrated quantity of light received by said photosensitive member, means including a voltage divider for determining the potential of the cathode of said thyristor, and means operating in conjunction with said voltage divider for lowering the potential of the cathode of said thyristor in response to a relatively high rate of charging said integration capacitor caused by nearness of said photosensitive member to a subject from which light is reflected, so that an increasing potential supplied to said grid wilL exceed the potential of said cathode at an earlier time, thus making said thyristor conductive and initiating operation of said interrupting means at an earlier time than if said cathode potential had not been reduced.

Claim 7

Electronic flash apparatus comprising a flash tube for emitting photographic light during discharge of the tube, means for interrupting discharge of said tube to stop emission of light therefrom, and control means for controlling operation of said interrupting means, said control means including a photosensitive member responsive to light reflected from a subject being photographed, an integration capacitor charged through said photosensitive member, a thyristor having an anode, a cathode, and a control grid, said thyristor being effective when it becomes conductive in its anode-cathode path to initiate operation of said interrupting means, means connected to said photosensitive member and to the grid of said thyristor for supplying said grid with an increasing potential depending on the integrated quantity of light received by said photosensitive member, means including a voltage divider for determining the potential of the cathode of said thyristor, and means operating in conjunction with said voltage divider for lowering the potential of the cathode of said thyristor in response to a relatively high rate of charging said integration capacitor caused by nearness of said photosensitive member to a subject from which light is reflected, so that an increasing potential supplied to said grid wilL exceed the potential of said cathode at an earlier time, thus making said thyristor conductive and initiating operation of said interrupting means at an earlier time than if said cathode potential had not been reduced.