| 摘要 |
PURPOSE:To execute a proper exposure control without being influenced by variations of an optical conductive body such as CdS, by varying a current supplied to each transistor of a shutter circuit. CONSTITUTION:A photometric current mirror circuit is formed by a transistor (TR) Q1 in which the collector connected to the base has been connected to photometric CdS, a TR Q2 in which the collecter connected in series to said TR has been connected to the first current source Z1 and the collector has been connected to the base, a capacitor C1 by which the collector is charged in accordance with photometric voltage, a TR Q3 connected to the base CdS, a TR Q4 in which the collector connected in series to said TR and receiving a current supplied from the second current source Z2, etc. In this state, a shutter second time is controlled through the capacitor, a comparator COM to which a reference value has been set, etc. When a current supplied to the TRs Q2, Q3 from the electric power supplies Z1, Z2 is varied in accordance with a ratio gamma of logarithmic intensity of illumination of this CdS and a logarithmic resistance value corresponding to intensity of illumination, a proper exposure control is executed without being influenced by variations of the characteristics of CdS, etc. |
