| 摘要 |
PURPOSE:To compensate for changes in measuring condition owing to a difference between the shutter screen and a film using a simple time constant circuit. CONSTITUTION:A capacitor 38 starts charging timed for initial running of a shutter screen. Being center-oriented measurement, a photo diode 10 measures a reflected light from the shutter screen untill the screen reaches the center of the picture. Consequently, the terminal voltage of the capacitor 38 rises at a fixed rate. As the shutter screen runs to the center of the picture, the reflected light from a film enters the photo diode 10 causing a sharp increase in the light current. But, at the same time, a capacitor 26 starts charging to compensate for the sharp increase in the light current. This can maintain the voltage between the base and the emitter of a transistor 32 thereby preventing changes in the measuring condition. |
