| 摘要 |
PURPOSE:To enable the treatment of an input varying drastically witin a certain dynamic range of the subsequent processing circuit by controlling the output of a means of detecting an output reflected on an object to be measured according to an output of a means of detecting the position to be measured. CONSTITUTION:Upon the start of measuring distance, a projection element 2 and a projection lens 1 performs a scanning in linkage with a distance ring of a photography lens 17 and the resistance value of a variable resistance 9 increases. Reflected lights from the object to be measured enter a light receiving element 8 and the output of an operation amplifier 10 increases with the scanning to rise the voltage of a capacitor 12 until the peak value is latched. As the light of the projection element 2 is off the object and the reflected lights become weak, the ouput of a comparator 13 inverts and no current flows through a magnet 14, so that the scanning through the photography lens 17 is stopped at the focusing position. When the object being measured exists at a long distance, the resistance value of the feeding back variable resistance 9 is so large to ensure a large amplification factor of the operation amplifier 10 and thus, the operation can be performed in the same manner as in the case where the object exists at a short distance causing a strong reflected light. |
