| 摘要 |
PURPOSE:To correct the photometric photocurrent due to shutter curtain and film reflectance in a simple constitution, by varying the ratio of constant current which logarithmically compresses or elongates the photometric photocurrent, and varying the photocurrent amplification factor depending on the position of shutter curtain. CONSTITUTION:A photocurrent corresponding to photometry by TTL system of a photo detector SPD in a logarithmic compressing circuit 11 is logarithmically compressed depending on a constant current IREF from a constant current source 14, and is then logarithmically elongated depending on a constant current IREF' in a logarithmic elongating circuit 12, and is amplified according to the ratio of the constant current IREF to the constant current IREF'. Therefore, by accessing an ROM19 using the logarithmic value of an oscillation output from an oscillator 21 of an amplification factor controlling circuit 15 by a counter 20 as the address, when the current source 14 is controlled through a D/A converter 18, the constant current applied to the circuit 11 is varied with the position of the shutter curtain. Thus, by varying the photocurrent amplification factor, the measurement is corrected depending on the changes in the reflectance of the shutter curtain and film curtain in a simple constitution without requiring forming of random number pattern or the like on the shutter curtain, so that a high precision measurement may be achieved. |
