Abstract Electronic flash apparatus for photographic purposes, wherein a flash tube is discharged to produce the desired light, and the discharge is terminated when sufficient light has been produced. The determination of when to terminate the discharge is accomplished by integrating the light reflected from the subject being photographed. In order to avoid the over-exposure which frequently occurs when apparatus of this general type is used for taking photographs at short distances, there is an impedance incorporated in the discharge circuit in front of the flash tube, and a commutating capacitor is connected to an intermediate tap in this impedance, and to an electronic switch, the commutating capacitor and switch being in parallel with the flash tube and a thyristor which is in series with the flash tube. A resistor bypasses the commutating capacitor. A connection from the junction between the commutating capacitor and the electronic switch goes through a break-down diode and another capacitor to the junction between the flash tube and its thyristor.
Electronic flash apparatus comprising a storage capacitor, a flash tube and a thyristor in series with each other and in parallel with said storage capacitor, ignition means for igniting said flash tube so that current from said storage capacitor may flow through said tube to create a flash of photographic light therein, and extinction means for stopping flow of current through said tube to stop emission of light therefrom when sufficient light for the photographic purpose has been produced, said extinction means including an impedance located in the discharge circuit between said storage capacitor and said tube, said impedance having an intermediate tap, a commutating capacitor and an electronic switch connected in series with each other and in parallel with said tube and thyristor through said intermediate tap, a by-pass resistor in parallel with said commutating capacitor and a portion of said impedance, a third capacitor and a potentiometer circuit in series with each other and in parallel with said thyristor, the gate of said thyristor being connected to an intermediate point of said potentiometer circuit, and a circuit connection from a junction between said third capacitor and said potentiometer circuit to a junction between said commutation capacitor and said electronic switch, said circuit connection including diode means and a fourth capacitor in series with each other.
Claim 2
Dependent Claim
217 words
Electronic flash apparatus comprising a storage capacitor, a flash tube and a thyristor in series with each other and in parallel with said storage capacitor, ignition means for igniting said flash tube so that current from said storage capacitor may flow through said tube to create a flash of photographic light therein, and extinction means for stopping flow of current through said tube to stop emission of light therefrom when sufficient light for the photographic purpose has been produced, said extinction means including an impedance located in the discharge circuit between said storage capacitor and said tube, said impedance having an intermediate tap, a commutating capacitor and an electronic switch connected in series with each other and in parallel with said tube and thyristor through said intermediate tap, a by-pass resistor in parallel with said commutating capacitor and a portion of said impedance, a third capacitor and a potentiometer circuit in series with each other and in parallel with said thyristor, the gate of said thyristor being connected to an intermediate point of said potentiometer circuit, and a circuit connection from a junction between said third capacitor and said potentiometer circuit to a junction between said commutation capacitor and said electronic switch, said circuit connection including diode means and a fourth capacitor in series with each other.
Claim 3
Dependent Claim
20 words
Apparatus as defined in claim 1, wherein said circuit connection also includes a resistor in parallel with said diode means.
Claim 4
Dependent Claim
14 words
Apparatus as defined in claim 1, wherein said diode means is a break-down diode.
Claim 5
Dependent Claim
29 words
Apparatus as defined in claim 1, wherein said diode means is a series of forwardly directed diodes faced in a direction from said third capacitor to said fourth capacitor.