| 摘要 |
An automatic focusing device has a rangefinder CCD sensor unit that measures a defocus amount with respect to the image of an object which is focused by an optical system. A focusing lens group of the optical system is driven into a focusing position based on the measured defocus amount. An object image moving speed, at which the image of the object moves, is calculated based on at least two defocus amounts which are measured. If the difference between a present defocus amount and a preceding defocus amount is smaller than a predetermined value, the focusing lens group is driven to move the focusing position at a tracking speed corresponding to the object image moving speed. If the difference is equal to or greater than the predetermined value, the focusing lens group is driven at a previously calculated object image moving speed. Even if an object moves out of a rangefinding zone while the object-in-motion is being tracked for focusing, the automatic focusing device keeps tracking the object, causing the focusing lens group to focus on the object.
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