Control system for inhibiting a calculating system in an automatic focusing device

• US 5,896,174 A
• Filed: 04/18/1997
• Issued: 04/20/1999
• Est. Priority Date: 09/11/1992
• Status: Expired due to Term

• Current Assignee: PENTAX RICOH IMAGING COMPANY, LTD.
• Original Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Inventors: Nakata, Masahiro
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): Vu, Ngoc-Yen, VU, NGOC YEN T
• Application Number:
  US08/839,937
• Time in Patent Office: 732 Days
• Field of Search: 348/345, 348/348, 348/349, 348/351, 348/352, 348/353, 348/354, 348/355, 348/356, 396/79, 396/80, 396/81, 396/82, 396/95, 396/93, 396/94, 396/138, 396/139, 396/78, 396/130, 396/147, 396/435, 396/96
• US Class Current: 348/348
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method
• CPC Class Codes: H04N 23/695 Control of camera direction for changing a field of view, e.g. pan, tilt or based on tracking of objects

Abstract

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.

Claims

1. An automatic focusing device used in a camera capable of executing successive exposures, said successive exposures being taken when said automatic focusing device is in a focus prediction mode, said automatic focusing device comprising:

an optical system including a focusing lens group;

a defocus measuring system that obtains defocus amount data of an image of an object to be tracked with respect to a film plane;

a memory which stores a defocus amount data;

a control system which determines whether a currently obtained defocus amount data is a defocus amount data of said image of the object to be tracked or of an image of another object, based upon a change in the currently obtained defocus amount data in relation to a previously obtained defocus amount data which is stored in said memory;

a calculating system that calculates a relative speed of movement of said image of the object to be tracked along an optical axis of said focusing lens group with respect to said film plane based on the previous defocus amount data stored in said memory and the defocus amount currently obtained by said defocus measuring system; and

a lens driving system that drives said focusing lens group along the optical axis of said optical system,

wherein said lens driving system drives said focusing lens in accordance with a previously calculated relative speed when said control system determines that said currently obtained defocus amount data is a defocus amount data of said image of said another object, and drives said focusing lens in accordance with a currently calculated relative speed when said control system determines that said currently obtained defocus amount data is the defocus amount data of said image of said object to be tracked.

2. An automatic focusing device according to claim 1, said lens driving system driving said focusing lens group according to a last calculated relative speed stored in said memory when said control system determines that said current defocus amount is defocus amount data of another object.

3. An automatic focusing device according to claim 1, said lens driving system driving said focusing lens group at a constant speed when said control system determines that said current defocus amount is defocus amount data of another object.

4. An automatic focusing device according to claim 1, further comprising an enabling system that enables said calculating system to calculate said relative speed when said currently obtained defocus amount is within a predetermined amount of said preceding obtained defocus amount data.

5. An automatic focusing device according to claim 1, said control system further including a system that establishes an object tracking mode when said currently obtained defocus amount data has changed in excess of a predetermined amount in relation to a preceding obtained defocus amount data.

6. An automatic focusing device according to claim 1, further comprising a shutter release system that actuates a shutter, exposes a photographic film, and winds the photographic film.

7. An automatic focusing device according to claim 6, further comprising a system that suspends said calculation of relative speed when said shutter release system is actuated and a system that resumes said calculation of said relative speed when said winding is complete.

8. An automatic focusing device according to claim 7, said lens driving system driving said focusing lens group according to a relative speed of movement calculated prior to actuation of said shutter release system when said shutter release system is actuated.

9. An automatic focusing device according to claim 8, said lens driving system driving said focusing lens group at three times said relative speed calculated prior to actuation of said shutter release system when said currently obtained defocus amount data, measured after said winding is complete, has changed in excess of a predetermined amount of a preceding obtained defocus amount data.