Automatische Fokussierungsschaltung für automatische Fokusanpassung in Abhängigkeit von Videosignalen.

摘要

In an automatic focusing apparatus of a video camera, a first focus evaluating value which steeply changes and a second focus evaluating value which gently changes relative to the position of a lens, are detected in response to a video signal obtained in an image sensing circuit (4). A switching circuit (19) alternately selects the first and second focus evaluating values every one field, to apply the same to in-focus state detecting circuits (20, 21), respectively. The in-focus state detecting circuits (20, 21), together with a focusing motor control circuit (10), perform an automatic focusing operation by hill-climbing control. In addition, a calculating circuit (22) calculates the relative ratio of the first focus evaluating value to the second focus evaluating value. The focusing motor control circuit (10) sets the rotational speed of a focusing motor (3) to a normal speed when the calculated relative ratio is smaller than a predetermined value while setting the rotational speed of the focusing motor (3) to a low speed when it is larger than the predetermined value. Therefore, a lens (1) is moved at low speed when the focusing lens is in the vicinity of the in-focus position while being moved at high speed when it is in the defocused state.