Patent GB-1511342-A (GB)
Title: Camera exposure control systems
IPC: G03B9/08
Filed: 1975-04-14
Abstract: 1511342 Cameras WEST ELECTRIC CO Ltd 14 April 1975 [16 April 1974] 15169/75 Heading G2A  A camera has an exposure control device which comprises shutter blades 4, 5 which are movable between an adjustable open position and a closed position by a rotatable stepping motor 3 under the control of circuitry which also controls a film transport motor 42 for moving the film by one picture frame when a switch 12 is actuated by the movement of the blades to their closed position after an exposure. The aperture defined by the shutter blades is determined by detecting the brightness of a subject by a photo-cell 13 the resultant voltage being compared with that produced by feeding pulses from a pulse generator 16 to a ring counter which produces a corresponding voltage, the voltages being compared by a differential amplifier forming part of the opening pulse generator 15, see also Figs. 2A and 2B (not shown), and the output of which feeds the correct number of pulses to the motor 3 to provide the optimum aperture. The exposure time is then determined by an integrating circuit comprising a photo-cell 19 and a capacitor 20, an integrated signal generator 21, an integration level control circuit 22, a closing pulse signal generator 23 and the pulse generator 16. The voltage across the capacitor 20 is applied to the generator 21 which is also supplied with pulses from the generator 16 and the opening pulse signals from the generator 15 via the circuit 22 so that the correct closing pulse signals are transmitted through the circuit 23 to the motor 3 a predetermined time after the opening pulse signals have been transmitted to the motor 3. In operation when a shutter release button is depressed a switch 24 is closed to activate a setting signal generator and then a power supply connection circuit 35 to connect a battery 27 to the various circuits. When the blades are closed the switch 12 is closed to actuate a reset signal generator 30 which sends a signal via a line 37 to reset the circuits. The generator 30 also sends a signal to a rectifier 40 which causes a transistor 41 to conduct and so start the film transport motor 42. When the film has been moved a switch 43 is closed to short-circuit motor 42 and stop it. A transistor 50 short-circuits the gate electrode of a control rectifier 26 to prevent erratic operation of the stepping motor 3 during film transport. A switch 52 is used for film advance e.g. to a start position of the film. The camera may be operated by a signal pulse at a terminal 52' and which is transmitted to the rectifier 26 via a diode 53 to cause the stepping motor 3 to operate for one exposure and the motor 42 to transport the film for one frame. Two time-spaced pulses may be sequentially applied at the terminal 52', the first pulse causing operation of the motor 3 for one exposure and the second pulse preventing operation of the motor 42 thereby to allow multiexposure of the film. A delay circuit 57 feeds one input terminal of a NOR gate 58 only after the  second pulse is received, to produce an output which is fed to a rectifier 60 whereby transistors 61 and 62 became conductive to short-circuit the rectifier 40 and so prevent operation of the motor 42. Switch 64 is for manual operation for obtaining multi-exposure of the film. A transistor 63 ensures turning off of the rectifier 60 in response to a signal from the stepping motor 3. The circuitry may be controlled remotely by means of pulses transmitted by a wireless system. This may be by opening and closing a switch or by amplitude or frequency modulations. Alternatively, remote control may be by light or sound remote control systems.