CdS photoresistor as electronic photometric element circuit diagram

In mid-range cameras, CdS photoresistor is used as an electronic photometric element. Light shines from the orifice plate onto the CdS photoresistor, moving the density plate to balance the circuit. The two LED light-emitting diodes emit uniform light, indicating appropriate exposure. If only one of them lights up but the other does not, it means underexposure or overexposure. At this time, moving the density plate can achieve the purpose of correct exposure. The thermistor RM (1kΩ) in the circuit plays a temperature compensation role to compensate for the error caused by the temperature change of the photoresistor.