Electronic photoflash cct. - has switch controlled by photoelectric meter to switch off thyristor and flash

摘要

Photographic electronic flash lamp has the flash duration controllable in dependence on the amount of light reflected from the exposure object. A thyristor is in series with the flash tube and a capacitor, and is shut off by a photoelectric meter when a settable value for the reflected amount of light is attained. A series arrangement of an electronic switch that can be controlled by the meter and a capacitor is in parallel with the thyristor flash tube and first capacitor, and an inductance is inserted between the flash tube and the first capacitor. Pref. the second capacitor has a negative bias. The thyristor can be reliably switched off at nay given time instant during the flash duration, without overexposure of the object.