The invention utilizes an autofocus system (806) that is capable of very fast changes in focus over a relatively small portion of the focus range of the focusing system. When operating continuously in a repeating series of images or frames such as are found in preview mode or in video capture, autofocus images are captured before and after each video frame wherein the autofocus images have different focus settings than the images in the series. The autofocus images are then evaluated for focus quality to determine whether focus adjustments are needed.