Patent GB-1517723-A (GB)
Title: Camera exposure control systems
IPC: G03B7/091
Filed: 1975-07-04
Abstract: 1517723 Automatic camera exposure control ASAHI KOGAKU KOGYO KK 4 July 1975 [17 July 1974 2 Aug 1974 3 Oct 1974 5 Nov 1974] 28331/75 Headings G2A and G3N A camera has an exposure control circuit which generates and stores a number of pulses dependant upon incident light intensity and, if the number lies outside a predetermined range, adjusts an exposure parameter in accordance with the extent to which the stored number deviates from the range. Preferably, diaphragm aperture is manually set, and shutter speed is controlled according to the stored count, the diaphragm value being automatically re-adjusted if the count reaches the limits of the range. In Fig. 3, the number of pulses generated at 1 is inversely proportional to light intensity and also depends on film speed and the manually set aperture value. The pulses are counted at 2. If the light intensity is so low that the count reaches the right hand end of counter 2, a switch 5 opens a gate 6 and closes a gate 3 so that the remaining pulses are directed to a diaphragm opening circuit 7. If light intensity is so high that the count has not reached the second stage of counter 2 by the time a timer 14 times out, then pulses from a second oscillator are passed through a gate 17 to a diaphragm closing circuit 18 until the second stage is reached. Upon shutter opening a second counter 31 counts pulses from a third oscillator 30 and when the counts at 31 and 2 are the same a coincidence detector 32 closes the shutter. In Fig. 4 (not shown), the shutter is controlled using a reversible counter (36), in Fig. 5 (not shown) by reversing all the stages of the first counter (38) then feeding in comparison pulses until all stages are in a 1 state and in Fig. 6 (not shown) by switching in a timing resistance whose value depends on the count. Figs. 12 to 23 (only Fig. 21 shown) use two shift registers. In Fig. 21, register 72 receives the photodependant pulses and register 87 stores two reference signals at 87c, d. A second oscillator 63 is then turned on. If light intensity is too low, the signal in 72 is to the right of 87c and gate 88, switch 89 and SCR 90 open a gate 91 to direct pulses from 63 to the left hand end of the registers. The signal in 72 reaches the right hand detector 65 and operates a diaphragm opening circuit 71 until the signal in stage 87c reaches detector 65. If light intensity is too high, a gate 94 is opened, pulses are directed to the right hand end of the registers and a diaphragm closing circuit 79 is operated. In Fig. 15 (not shown) aperture opening beyond a pre-set value is prevented to avoid undue reduction in depth of field. Figs. 25, 26, 27 (not shown) use a single shift register. If the count is outside the range a resistor is selected according to the state of the register and the diaphragm is adjusted by a voltage operative for a time dependant on the resistor. Figs. 29, 30 (not shown) use a counter. If the count is outside the range, a resistor is selected according to the state of the counter and the diaphragm is adjusted by a voltage whose magnitude depends on the resistor.