| 摘要 |
PURPOSE:To perform smooth focusing control and to increase a dynamic range by varying the quantity of light emitted from a light emission part which projects infrared light as spot light stepwise with the integration time of an integration circuit which integrates the detection output of a photodetecting element. CONSTITUTION:Two output currents of a semiconductor position detector(PSD) are converted by current-voltage converters 1 and 1' into voltages, and signal voltages VA and VB generated by integration circuits 3 and 3' are converted into digital values by and A/D converter 4. Then, a logic circuit or microcomputer 5 performs arithmetic VA+VB corresponding to the quantity of photodetection of the PSD and controls an integration time and the quantity of light emission of a light emitting LED 7 with th arithmetic value. Pulse modulation is imposed upon the light emitted by the LED 7 and the integration time is controlled by controlling the number of pulses to be integrated by the microcomputer 5, etc. Thus, the smooth focusing control is performed and the dynamic range can be increased. |
