GB922016A - Improvements in or relating to photographic cameras - Google Patents

Abstract

922,016. Photo-electric exposure control. MINISTER OF AVIATION. Nov. 16, 1961 [Aug. 18, 1960], No. 28645/60. Class 40 (3). [Also in Groups XX and XL (c)] Automatic aperture control means comprise a plurality of devices responsive to light from respective parts of a field of view and arranged to increase and/or decrease the aperture when any of them receives too little or too much light respectively. Four photo resistors E1- E4, Fig. 1, are arranged around the " format " F in the focal plane of the camera lens, and are in series with actuating windings of respective relays R1-R4. When photo resistors E1- E4 receive illumination satisfactory for exposure, the relays are as shown with no contacts made. The upper contacts of relays R1-R4 are in parallel so that if any one of photo resistors E1-E4 receives less than a predetermined level of illumination the corresponding upper contact closes to energize a winding O of a motor M to open the aperture. Since the lower contacts are in series, every one of photo resistors E1-E4 must receive more than a predetermined illumination before winding C is energized to close the aperture. The predetermined levels are adjusted by switch S which controls the current in bias windings of relays R1-R4. In modifications, slave relays may be employed, and connections may be such that one photo resistor may initiate closure of the aperture but all are necessary to open it. In a second embodiment, Fig. 3 (not shown), the photo resistors are connected in series with ohmic resistors, the junctions being connected through diodes to the base of a transistor which, acting as an emitter follower, controls the motor.