| 摘要 |
The automatic diaphragm controlling device comprises an electric source, a servomotor having a single driving coil for driving a diaphragm of an objective lens, a scene light indicating voltage generating circuit and a reference voltage generating circuit energized by the electric source, respectively, the servomotor being controlled by the difference between the output voltages of both circuits so that a proper exposure is obtained. The servoamplifier comprises a first operational amplifier with its inverted input terminal connected to the non-inverted input terminal of a second operational amplifier through a first resistor while the non-inverted input terminal of the first operational amplifier is connected to the inverted input terminal of the second operational amplifier through a second resistor, the junction between the first resistor and the non-inverted input terminal of the second operational amplifier being connected to the reference voltage generating circuit while the junction between the non-inverted input terminal of the first operational amplifier and the second resistor is connected to the scene light indicating voltage generating circuit, a negative feedback resistor being connected between the output terminal and the inverted input terminal of each operational amplifier, the servomotor being connected between the output terminals of both operational amplifiers. The use of two operational amplifiers permits a simple construction of the circuit while one source - one coil system of the controlling device is insured and power is greatly saved.
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