The invention relates to electronic exposure control arrangements for photographic cameras of the type including a timing circuit incorporating a photosensitve element exposed to scene light. A shutter-control magnet, for example, keeps the camera shutter open until the timing circuit determines that a predetermined total amount of light has been received by the photosensitive element, whereupon the timing circuit causes the shutter-control magnet, for example, to become deenergized, thereby closing the shutter. The type of exposure control arrangement in question additionally includes means for automatically causing the shutter to close after the elapse of a predetermined time interval, so that the shutter cannot remain open longer than the predetermined time interval.
It is already known, for example, to limit the duration of the exposure time interval during which the shutter stays open by exposing the photosensitive element of the scene-light-dependent timing circuit to light from a light source in the camera. The intensity of light from this light source is so selected that, if the actual scene light is of a predetermined low brightness level, the automatic timing circuit will cause the exposure to terminate after the elapse of an exposure time interval equal to the longest exposure time interval for which a proper exposure can be performed. This known expedient has the disadvantage that the use of the separate light source during the entire exposure operation involves a considerable additional current drain, for example upon the camera battery.
USPTO Backgrounds
USPTO Backgrounds