Automatic focusing circuit for automatically matching focus in response to video signal

Abstract From the Canadian patent

In an automatic focusing circuit of a video camera, an automatic focusing operation is performed in response to a first focus evaluating value which is steeply changed and a second focus evaluating value which is gently changed, in response to the position of a lens in which the first and second focus evaluation values are generated in response to a video signal obtained in an image sensing circuit. When a comparator determines that the first focus evaluating value does not reach a predetermined reference value, an in-focus state detecting circuit and a focusing motor control circuit perform an intermittent automatic focusing operating every other field in response to the second focus …