| 摘要 |
<p>A photographic camera includes an electronic shutter control circuit for controlling a camera shutter mechanism while permitting either time limited or extended time exposures under low scene light conditions. The shutter control circuit includes a timing device for closing the shutter comprising a first timer responsive to prevailing scene light conditions and a second timer having a fixed predetermined time constant, the second timer being adapted to close the shutter after a fixed time interval to eliminate extended time exposures. A network for indicating the adequacy of scene light for obtaining a proper exposure within the fixed time interval is coupled to the light responsive timer through a reversed biased diode to effectively render that timer incapable of controlling the shutter mechanism under low scene light conditions. A selectively actuatable switch member operably connected to the shutter control circuit functions to override the second timer, and to enable the light responsive timer to be operated in low scene light conditions if an extended time exposure is preferred by the camera operator.</p> |
