| 摘要 |
PURPOSE:To make possible continuous focusing by providing differentiating and integrating circuits, etc. and discriminating whether the position of a lens is before or behind the position where it focuses. CONSTITUTION:The detecting signal of a photo detecting means 4 is supplied to an integrating circuit 22 by way of a shift register 10 or the like. As the output of the integrating circuit, the differential crest value output integrated along the characteristic curve 40 of crest type according to the distance D on the optical path between a lens 2 and photo detecting means 4 is obtained. Here, if the focus is matched, the output level of the integrating circuit 22 becomes maximum because the image on the photo detecting means 4 is high in contrast. The distance D on the optical path of this time is let to be d. Next, the output of the integrating circuit 22 is supplied to an integrating circuit 24 and when D=d, no output voltage is generated at all. When D<d, the output voltage in the positive direction is obtainable and when D>d, the output voltage in the negative direction. According to this output, the lens 2 is moved by a motor 26, whereby the continuous focusing may be performed. |
