| 摘要 |
PURPOSE:To reduce the exposure error in a wide range from a low temperature to a high temperature, by inserting a series or serial-parallel resistance circuit including a thermistor in a DC ammeter as an exposure controller for a camera or the like. CONSTITUTION:When a power switch S1 is turned on, the voltage of a power source battery E is supplied to an exposure circuit through a constant voltage circuit RF, and a current is flowed to an ammeter ME through a photodetector RX. The aperture value of a lens is determined on a basis of the deflection angle of the needle of the ammeter due to this current value. In respect to correction of a temperature compensating circuit, values of resistances R1 and Rs are selected so as to make equation true, thus minimizing the exposure error agaist the variation of temperature in a wide range from a low temperature to a high temperature. In equation, Me, R1, Rs, and Rso are the winding resistance value of the ammeter, the resistance value of a correcting resistance, the resistance value of a thermistor, and the resistance value of the thermistor at a normal temperature respectively. |
