| 摘要 |
PURPOSE:To stabilize the focusing operation of an object being low contrast by reducing offset voltage equivalent to an A/D conversion output at the time of light-shielding from the DC bias of an input signal for an A/D converter at the time of regular photographing before the focusing operation. CONSTITUTION:A microcomputer 50 sets a focusing mechanism 60 in a close state before the start of the focusing operation, sets a focus evaluation value obtained from an evaluation value generation circuit 45 as an offset value, converts it into PWM and outputs it to an offset voltage generation circuit 40. The circuit 40 amplitude-detects 41 a PWM output, converts it into DC voltage, adjusts 43 a prescribed gain and holds 44 it as offset voltage. At the time of regular photographing, offset voltage is inputted to a subtracter 22, offset voltage is subtracted from the DC bias which is set through a resistance 21 in an input signal for the A/D converter 5e and it is inputted to the circuit 45. Thus, the DC offset voltage error of the A/D converter 5e is removed from the obtained focus evaluation value and the stable focusing operation is realized. |
