Patent GB-1485165-A (GB)
Title: Exposure control means
IPC: G03B7/083
Filed: 1974-10-24
Abstract: 1485165 Electronically controlled shutters EASTMAN KODAK CO 24 Oct 1974 [24 Oct 1973 22 May 1974] 46068/74 Heading G2A A camera shutter is electronically controlled such that it may operate in either a light dependent mode or a fixed exposure mode, mode selection being automatic unless the fixed exposure mode is over-ridden by the operator.  Electronic controls (Fig. 2). This comprises a fixed interval timer 104 and a light dependent timer 102. A mode selector 110 and shutter trigger 106 are also included. (A) Timer 104. When the camera is operated switch S 1 supplies power across the potential divider formed by resistor 124 and transistor 132. Terminal 130 is therefore held at an intermediate voltage. As the shutter opens switch S2 closes to earth transistor 132 and switch it "OFF". The potential of terminal 130 therefore commences to rise toward that of terminal 128, the rate of increase being dependant on the values of components 124-126. (B) Timer 102. The operational description is identical to (A) above except that 112 is not a fixed resistor. Its resistance is inversely related to the light intensity whereby the rate of increase of potential of terminal 122 is directly related to the light intensity.  (C) Mode Selector 110. Element 146 is similar to 112, described above, such that the voltage at 147 is directly related to the light intensity. The trigger 150 is such that below a predetermined voltage at 148 the terminal 111 is connected to ground, but above said voltage at 148 the terminal 111 is isolated. Thus under low light conditions the terminal 111 and hence terminal 122 are grounded and the circuit 102, B above, is disabled. At the same time a light emitting diode 154 is in circuit to indicate that the low light condition exists. At higher light levels the terminal 111 is isolated, light 154 goes out, and timer 102 is operative. (D) Trigger 106. The trigger circuit is of the same kind as that in (C) above, and is switched via "OR" gate 136 by a high voltage at either 122 or 130 to stop conduction through solenoid 108. Solenoid 108 prevents closing of the shutter when switched on. (E) Operation. If light is low, e.g. for exposure values of 1/30 second or larger, the timing circuit 102 is disabled, as described in (C) above, and the circuit 104 operates to raise the voltage of terminal 130 until it operates the "OR" gate 136. At higher light intensities the timing circuit 102 operates the terminal 122 of the "OR" gate (the circuit 104 not being disabled but operating too late to effect the exposure. Operation of the ganged over-ride switch S 3 -S 4  isolates circuit 102 from the disabling trigger 150, and grounds circuit 104, thereby leaving circuit 102 in control. Shutter mechanism (Fig. 1). Two linearly moving blinds 22, 24 are held to the right, as shown, in the cocked condition. Shutter release button 68 releases blind 22 by removing detent 36, and also operates switch S1 to energize the electronics. As blind 22 moves to the left switch S2 closes to initiate the timer 102 or 104. After a delay, determined as described above, the  solenoid 56 (108) is de-energized to release latch 44 or allow blind 24 to move to terminate the exposure. The shutter is re cocked by rightwards movement of abutment 60 which contacts projection 62, which in turn abuts projection 66.