Electronic exposure time measuring circuit with time indicator and shutter control means

Claim 1

An electronic exposure time measuring circuit with time indicator and camera shutter control means for opening a camera shutter, indicating the exposure time to be expected and closing the camera shutter at the end thereof, said device comprising a. a photoelectric detector (1) in line with b. a capacitor (2); c. amplifying means (7) for amplifying the voltage level of the capacitor, said amplifying means being switchable between a high ratio of amplification and a ratio of 1:1; d. a comparison stage (13) to which the amplified voltage is supplied for comparison with a pre-established comparison voltage, said comparison stage generating a pulse when the level of said amplified voltage reaches the level of said comparison voltage; e. electronic control means (16, 19) connected to said comparison stage and being operable in dependence on the pulse generated by said comparison stage, said control means switching the amplification ratio from the high ratio to the ratio of 1:1 upon receiving a first pulse and switching it back upon receiving a second pulse; f. a time indicator (17) connected to said control means for indicating the exposure time to be expected at a speed which corresponds to the high amplifying ratio of said amplifying means, said indicating device being started when said measuring circuit is put into operation, and being stopped by said control means when receiving said first pulse; g. a means (21) for controlling the mechanical elements of the camera shutter, said means being put into operation when said circuit is started to measure the exposure time and said means being put out of operation by said control means when receiving said second pulse.