| 摘要 |
1397482 Exposure meters ASAHI KOGAKU KOGYO KK 24 Sept 1973 [12 Oct 1972] 44714/73 Heading G2X An exposure meter comprises two emitter follower transistors Q 1 , Q 2 each having its emitter connected to a linearly variable exposure factor setting resistor VR 1 , VR 2 which in turn is connected to a constant current source (as shown FETs Q 3 , Q 4 with source resistors r 3 , r 4 ), means for applying to the base of transistor Q 1 a logarithmically compressed voltage corresponding to received light amount (as shown a CdS element R 1 and a diode D 1 ), means for applying to the base of transistor Q 2 a bias voltage having the same response to source voltage and ambient temperature variation as the log compressed voltage (as shown a resistor R 2 and a diode D 2 ) and a meter M connected to receive outputs from the resistors VR 1 , VR 2 to indicate whether the exposure factors set are correct with respect to the received light. If a photo-voltaic element is used instead of the CdS element R 1 , the bias voltage is obtained from an FET or Zener diode. The circuit is independent of voltage and temperature fluctuation and does not require non-linear resistors. |
