Autofocus control device having moving body tracking control

An autofocus control device for photographic device which forms an image of a subject on an image forming plane with a photographic lens, comprising:

• a drive to drive the photographic lens in an optical axis direction;
• a photoelectric conversion element to receive the image of the subject and to convert the image into electrical signals;
• a defocus amount computation device to compute a defocus amount, representing an amount of deviation of an image position formed by the photographic lens from the image forming plane, based on the output of the photoelectric conversion element;
• a drive position computation device to compute a position to which the photographic lens is to be driven for focusing based on the output of the defocus amount computation device;
• a drive position history storage device to store a history of drive position data for a predetermined number of computations of positions to which the photographic lens is to be driven;
• a field travel speed computation device to compute the subject field travel speed and direction from the difference between the most recent computation of the drive position and a computation of the drive position performed a predetermined number of computations prior to the most recent computation;
• a moving body determination device to determine whether the subject is a moving body;
• and
• a lens drive control to drive the photographic lens according to the result of the moving body determination device,
• wherein the moving body determination device determines that the subject is a moving body when the subject field travel speed obtained by the field travel speed computation device is not less than a predetermined value, and a change in direction of drive position between each respective drive position stored in the drive position history storage device and a drive position generated one time previous all match the direction of the subject field travel speed.

An autofocus control device to control focusing of an image of a subject on an image forming plane by a photographic lens, comprising:

• a defocus amount computation device to determine a defocus amount representing a deviation of a position of an image formed by the photographic lens from the image forming plane;
• a drive position computation device to compute a series of drive positions to which the photographic lens is to be driven based on the output of the defocus amount computation device and to store a history of the computed drive positions;
• a moving body determination device m determine whether the subject is a moving body based on the history of required drive positions by determining whether a change in direction of drive position between each successive computed drive position is the same;
• and
• a lens control to drive the photographic lens according to the drive speed computed by the drive speed computation device when the moving body determination device determines that the subject is a moving body.

An autofocus system for a camera having a photographic lens to focus on a subject, comprising:

• a defocus amount computation device to destining a defocus amount of a subject image representing a deviation of a position of an image formed by the photographic lens from an image forming plane;
• a drive position computation device to compute a series of drive target positions of the photographic lens based on the defocus mount determined by the defocus amount computation device and to store a history of the computed drive target positions;
• and
• a moving body tracking control system to determine a field travel direction for the subject and change in direction between successive drive target positions of the series of drive target positions based on the stored history of computed drive target positions and to determine that the subject is a moving body when the field travel direction is the same as the directions of change of the series of drive target positions.