| 摘要 |
PURPOSE:To compensate the difference of reflection factors between the shutter screen surface and film surface of a camera at the time of direct photometry by equivalently changing the capacitance of an integrating capacitor at a prescribed time to alter the integral time constant. CONSTITUTION:Before exposure, both a trigger switch SW1 and a changeover switch SW2 are closed and the photocurrent (i) of a light receiving element PD flows through the switch SW1, so that charge is not accumulated in an integrating capacitor C1 (capacitance C). When the switch SW1 is opened at the start of exposure, the output voltage Vout of an operational amplifier OP1 is expressed as shown in the equation 1. When the switch SW2 is opened after a prescribed time T0, said output voltage Vout is expressed like the equation 2. Thus, voltage V1 shown in the equation 2 shows the output voltage just before the opening of the switch SW2 and the integral time constant is changed, compensating the difference of reflection factors between the shutter screen surface and film surface. |
