| 摘要 |
PURPOSE:To widen the dynamic range of a photometric area by selecting the case that photometric operation is performed only by the junction capacitance of a silicon photodiode and the case that it is performed by adding a capacitor. CONSTITUTION:An external light brightness detection circuit 5 detects the condition of the brightness of an object and transmits it to a CPU 8. In the case the brightness of the object is lower than specified brightness, the CPU 8 turns off a transistor 7, so that the charge of the junction capacitance Cj of the silicon photodiode 6 is discharged to increase the inverted input terminal voltage Vn of an operational amplifier 1, and the amplifier 1 transmits inverted output to close a shutter. In the case the brightness of the object is higher than the specified brightness, the CPU 8 turns on the transistor 7, so that the capacitor 4 is connected, charge is performed by the photoelectric current of the silicon photodiode 6 to increase the terminal voltage Vn of the amplifier 1, and the amplifier 1 transmits the inverted output to close the shutter. |
