Electronic strobe flash apparatus for indirect and direct flash

Abstract

Electronic strobe flash apparatus includes a first energizable flashtube arranged to project light for reflection from a surface to illuminate a scene indirectly, and a second energizable flashtube arranged to illuminate the scene directly. A sequencing circuit controls the energization of both flashtubes so that the ratio of the indirect flash to the direct flash reflected from the scene is constant in instances where the reflected flash is above a minimum level. For this purpose, a light-sensitive circuit, arranged to sense light reflected from the scene, is coupled to the sequencing circuit. The sequencing circuit causes the indirect flash to be produced first. The light-sensitive circuit causes the sequencing circuit to (1) quench the first flashtube to extinguish the indirect flash, and (2) fire the second flashtube to produce the direct flash, when the light-sensitive circuit senses that a predetermined fraction of a desired total amount of light has been reflected from the scene. Then, the sequencing circuit quenches the second flashtube to extinguish the direct flash when the light-sensitive circuit has sensed the desired total amount of reflected scene light. If the light-sensitive circuit senses very little light following the energization of the first flashtube, indicating that insufficient indirect flash will be produced, the sequencing circuit quickly quenches that flashtube, thereby saving electrical energy that otherwise would be wasted. To regulate the indirect and the direct flash independently of the ambient light, a bandpass filter can be employed to remove from the light-sensitive circuit's output any contribution due to ambient light.