Electronic flash unit with preliminary flash for automatic timing

Claim 2

Electronic flash unit for use in creating an image on photosensitive material, comprising in combination, light-flashgenerating means for generating a preliminary flash, and a main flash immediately following said preliminary flash; a photoelectric element mounted to receive light corresponding to the light falling on said photosensitive material, said photoelectric element furnishing a first signal corresponding to the light falling thereon when energized; means for energizing said photoelectric element only during said preliminary flash; terminating means connected with said light-flash-generating means, for terminating said main flash in response to a terminating signal; and terminating signal furnishing means interconnected with said terminating means and said photoelectric element, for furnishing said terminating signal after a delay time period following said preliminary flash and thus the initiation of said main flash, said delay time period varying as a function of said first signal.

Claim 3

An electronic flash unit as set forth in claim 1, wherein said light-flash-generating means comprise a gaseous discharge tube having an ignition electrode.

Claim 4

An electronic flash unit as set forth in claim 2, wherein said light-flash-generating means further comprise ignition circuit means for furnishing a signal to said ignition electrode for starting said test flash; and additional circuit means for furnishing energy for said main flash while said flash tube is still ionized from said test flash.

Claim 5

An electronic flash unit as set forth in claim 3, wherein said gaseous discharge tube has a first and second main electrode; further comprising a first capacitor having a first terminal connected to said second main electrode, for furnishing the energy for said test flash; and wherein said additional circuit means comprise a second capacitor having a first terminal connected to said first main electrode and a second terminal, unidirectional conducting means for interconnecting said second main electrode and the second terminal of said second capacitor, said unidirectional conducting means interconnecting said terminals in such a manner that said second capacitor cannot discharge through said gaseous discharge tube, said additional circuit means further comprising a first switching element connected in parallel with said unidirectional conducting means and adapted to short circuit said unidirectional conducting means when the voltage difference between the second terminal of said second capacitor and the first terminal of said second capacitor reaches a predetermined voltage difference.

Claim 6

An electronic flash unit as set forth in claim 4, wherein said first switching element is a gas tube.

Claim 7

An electronic flash unit as set forth in claim 1, wherein said means for energizing said photoelectric element only during saId test flash comprise means for furnishing an operating voltage to said photoelectric element only during said test flash.

Claim 8

An electronic flash unit as set forth in claim 6, further comprising an integrating circuit connected between said photoelectric element and said terminating signal furnishing means for integrating said first signal; wherein said delay time period varies in dependence upon the integrated first signal; and wherein said means for furnishing an operating voltage to said photoelectric element comprise means for furnishing an operating voltage to said photoelectric element and to said integrating circuit, only during said test flash.

Claim 9

An electronic flash unit as set forth in claim 7, further comprising a DC voltage supply having a battery; wherein said DC voltage supply is connected in such a manner that it furnishes the energy for said light flash generating means and for said terminating means; and wherein said battery furnishes the operating voltage for said delay means, both during said test flash and said main flash.

Claim 10

An electronic flash unit as set forth in claim 4, wherein said means for energizing said photoelectric element only during said test flash comprise resistance means connected to furnish a voltage drop as a function of the discharge current of said first capacitor; and means for applying said voltage drop to said photoelectric element as an operating voltage therefor.

Claim 11

An electronic flash unit as set forth in claim 9, further comprising an integrating circuit connected to said photoelectric element for integrating said first signal; and wherein said means for applying said voltage drop to said photoelectric element comprises means for applying said voltage drop to said photoelectric element and to said integrating circuit.

Claim 12

An electronic flash unit as set forth in claim 10, wherein said photoelectric element is a photoresistor.

Claim 13

An electronic flash unit as set forth in claim 4, wherein the capacitance of said first capacitor is approximately one-tenth of the capacitance of said second capacitor.

Claim 14

An electronic flash unit as set forth in claim 4, wherein said resistance means comprise a resistor connected between the first main electrode of said gaseous discharge tube and the second electrode of said first capacitor.

Claim 15

An electronic flash unit as set forth in claim 10, wherein said integrating circuit comprises an integrating capacitor, connected to charge during said test flash in dependence upon said first signal, thus acquiring an integrator capacitor voltage corresponding to the total light received in said photoelectric element, at the end of said test flash; and blocking means for blocking the discharge of said integrating capacitor through said integrating circuit.

Claim 16

An electronic flash unit as set forth in claim 14, wherein said integrating circuit further comprises a transistor having a control circuit and an emitter-collector circuit; wherein said photoelectric element is connected in said control circuit; wherein a collector resistor is connected in said emitter-collector circuit; wherein said blocking means comprise a diode; and wherein said diode, in series with said integrating capacitor is connected in parallel with said collector resistor.

Claim 17

An electronic flash unit as set forth in claim 14, wherein said terminating means comprise a quench tube, having a first and second main quench tube electrode and a quench-tube ignition electrode, connected in parallel with said gaseous discharge tube; and wherein said terminating signal is a signal applied to said ignition electrode.

Claim 18

An electronic flash unit as set forth in claim 16, wherein said means for furnishing said terminating signal comprise a quench-tube ignition circuit connected to said quench-tube ignition electrode, said quench-tube ignition circuit having a second switching element; and wherein said terminating signal is generated in response to activation of said second switching element.

Claim 19

An electronic flash unit as set forth in claim 17, wherein said means for generating said terminating signal further comprise delay means interconnecting said integrating capacitor and said second switching element.

Claim 20

An electronic flash unit as set forth in claim 18, wherein said delay means comprise a delay capacitor; means for applying a DC voltage to said delay capacitor; circuit means for controlling the discharge of said delay capacitor in dependence on said integrator capacitor voltage; and wherein activation of said second switching element takes place when the voltage on said delay capacitor is less than a predetermined voltage value.

Claim 21

An electronic flash unit as set forth in claim 19, wherein said second switching element is a thyristor, having a thyristor control electrode and an anode-cathode circuit; wherein said anode-cathode circuit of said thyristor is connected in said quench-tube ignition circuit; wherein said delay means comprise voltage-divider means having a voltage-divider tap for furnishing voltage to said ignition electrode of said thyristor; and means for raising the voltage at said voltage-divider tap when the voltage on said delay capacitor is less than said predetermined voltage value.

Claim 22

An electronic flash as set forth in claim 20, wherein said means for raising the voltage at said voltage-divider tap comprise a second transistor having an emitter-collector circuit connected in such a manner that the voltage at said voltage-divider tap is below the activation point for said thyristor when said transistor is conductive; and means for blocking said second transistor when said voltage on said delay capacitor is less than said predetermined voltage value.