초록 ▼

An automatic focusing circuit in a video camera separates a high frequency component from the video signal obtained in an image sensing circuit 4 for every field. After the separated high frequency component is integrated in an integration circuit 10, the result is converted into a digital value by

An automatic focusing circuit in a video camera separates a high frequency component from the video signal obtained in an image sensing circuit 4 for every field. After the separated high frequency component is integrated in an integration circuit 10, the result is converted into a digital value by an A/D converter 11 and is applied to a holding circuit 12 as a focus evaluating value. The holding circuit 12, which comprises first to fifth memories coupled in series, always holds the newest successive five focus evaluating values. The largest focus evaluating value is detected by the maximum value detecting circuit 18 for every field and is applied to a memory 19. The maximum value is compared with the maximum value one field before held in a memory 20 in a comparator circuit 21. If the newest maximum value in the memory 19 is decreased, a focusing motor control circuit 22 inverts the rotational direction of the focusing motor 3. Thus, since the focusing ring is slightly vibrated in the maximal point of the maximum value of the detected focus evaluating value, a focusing lens can be held in the in-focus position.

대표청구항 ▼

An automatic focusing circuit for automatically matching the focus in response to a video signal obtained from an image sensor, comprising: focus evaluating value detecting means for detecting a level of a high frequency component of the video signal obtained from the image sensor every constant per

An automatic focusing circuit for automatically matching the focus in response to a video signal obtained from an image sensor, comprising: focus evaluating value detecting means for detecting a level of a high frequency component of the video signal obtained from the image sensor every constant period, converting the level into a focus evaluating value which takes the maximum value in the in-focus position or a focus evaluating value which takes the minimum value in the in-focus position, and sequentially supplying the same, first holding means connected to said focus evaluating value detecting means for holding a plurality of focus evaluating values successively obtained every said constant period, maximum value/minimum value detecting means for detecting the maximum value or the minimum value of said plurality of successively focus evaluating values held in said first holding means, and focus controlling means responsive to an output of said maximum value/minimum value detecting means for controlling the focus.