| 摘要 |
Electronic flash apparatus for photographic purposes, in which the duration of the flash is automatically regulated in accordance with the quantity of light reflected from the subject being photographed. The discharge of the flash tube is controlled by a thyristor in series with the flash tube. The circuit is so arranged that the voltage drop occurring in the discharge section of the flash tube when the tube is ignited, causes the thyristor to become conductive, so that the current from the usual storage capacitor can flow through the flash tube and through the thyristor in series with it, to provide the desired flash. The flash is terminated, when a measuring and integrating device receives sufficient light reflected from the subject being photographed, by a surge of commutating or counter current through the flash tube and its series thyristor, this surge being produced in part by an impedance or choke and an associated capacitor and second thyristor, the control grid or gate of the second thyristor being connected to the measuring and integrating device.
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