FOCUS ADJUSTING METHOD AND FOCUS ADJUSTING DEVICE

• US 20090028539A1
• Filed: 07/22/2008
• Published: 01/29/2009
• Est. Priority Date: 07/24/2007
• Status: Active Grant

• Current Assignee: PENTAX RICOH IMAGING COMPANY, LTD.
• Original Assignee: Hoya Corporation
• Inventors: NAKAHARA, Naoto
• Granted Patent: US 7,831,138 B2
• Time in Patent Office: Days
• US Class Current: 396/104
• CPC Class Codes: G02B 7/38 measured at different points on the optical axis , e.g. focussing on two or more planes and comparing image data
• CPC Class Codes: G03B 13/36 Autofocus systems

Abstract

A focus adjusting method for adjusting focus by moving a focusing lens group of a photographing optical system, wherein the focus adjusting method includes a first search stage at which a focus search operation is performed based on an image formed in a large focus area while the focusing lens group is moved stepwise over an entire range of movement thereof from the near extremity to the far extremity, and a second search stage at which the focus search operation is performed, based on images formed in small focus areas, at front and rear close vicinities of the in-focus position while the focusing lens group is moved stepwise over a portion of the entire range of movement thereof.

Claims

1. A focus adjusting method for adjusting focus by moving a focusing lens group of a photographing optical system,

wherein said focus adjusting method performs a focus search process in which a focus state is obtained to detect an in-focus position of said focusing lens group based on a contrast of an image formed by said photographing optical system, in one of at least one large focus area and each of a plurality of small focus areas included in said large focus area, while said focusing lens group is moved stepwise from one toward the other of a near extremity and a far extremity, and moves said focusing lens group to said in-focus position,

wherein said focus adjusting method comprises:

a first search stage at which a focus search operation is performed based on an image formed in said large focus area while said focusing lens group is moved stepwise over an entire range of movement thereof from said near extremity to said far extremity, and

a second search stage at which said focus search operation is performed, based on images formed in said plurality of small focus areas, at front and rear close vicinities of said in-focus position while said focusing lens group is moved stepwise over a portion of said entire range of movement thereof.

2. The focus adjusting method according to claim 1, wherein said focusing lens group is moved stepwise by a first pitch of movement at said first search stage, and

wherein said focusing lens group is moved stepwise by a third pitch of movement at said second search stage, said third pitch of movement being narrower than said first pitch of movement.

3. The focus adjusting method according to claim 1, further comprising a focusing drive stage which is performed after said second search stage and at which said focusing lens group is moved to an in-focus position obtained at said second search stage.

4. The focus adjusting method according to claim 1, further comprising a third search stage which replaces said second search stage when said in-focus position is not obtained at said first search stage,

wherein, at said third search stage, said focus search operation is performed based on said image formed in said large focus area while said focusing lens group is moved stepwise over said entire range of movement thereof with a second pitch of movement which is narrower than said first pitch of movement and wider than said third pitch of movement.

5. The focus adjusting method according to claim 4, further comprising a fourth search stage, at which said focus search operation is performed based on said images formed in said plurality of small focus areas while said focusing lens group is moved stepwise over a portion of said entire range of movement thereof at front and rear close vicinities of an in-focus position obtained at said third stage.

6. The focus adjusting method according to claim 5, further comprising a focusing drive stage which is formed after said fourth search stage and at which said focusing lens group is moved to an in-focus position obtained at said fourth search stage.

7. The focus adjusting method according to claim 4, further comprising a fifth search stage at which said focus search operation is performed based on said images formed in said plurality of small focus areas while said focusing lens group is moved stepwise over said entire range of movement thereof by said third pitch when said in-focus position is not obtained at said third search stage.

8. The focus adjusting method according to claim 7, further comprising a focusing drive stage which is performed after said fifth search stage and at which said focusing lens group is moved to an in-focus position obtained at said fifth search stage.

9. The focus adjusting method according to claim 1, wherein said plurality of small focus areas comprise:

first small focus areas formed by dividing said wide focus area; and

a second small focus area which overlap said first small focus areas.

10. The focus adjusting method according to claim 1, wherein, in the case where said large focus area comprises a plurality of large focus areas, said second search stage, said third search stage, said fourth search stage and said fifth search stage are carried out on one of said plurality of large focus areas in which an in-focus position at a shortest distance is obtained at said first search stage and on said plurality of small focus areas included in said one of said plurality of large focus areas.

11. The focus adjusting method according to claim 1, wherein said second search stage, said third search stage, said fourth search stage and said fifth search stage are carried out in the case where said in-focus position obtained at said first search stage is closer to a predetermined distance.

12. The focus adjusting method according to claim 11, further comprising a focusing drive stage at which said focusing lens group is moved to said in-focus position in the case where said in-focus position is not closer to said predetermined distance.

13. The focus adjusting method according to claim 1, further comprising a photographing-mode selecting stage for selecting a photographing mode from among various photographing modes including macro mode and super-macro mode,

wherein said first search stage and subsequent search stages are carried out in the case where one of said macro mode and said super-macro mode is selected at said photographing-mode selecting stage, and

wherein said focus adjusting method further comprises a focusing drive stage at which a focus search operation is performed based on said image formed in said large focus area while said focusing lens group is moved stepwise over said entire range of movement thereof to move said focusing lens group to an in-focus position obtained by said focus search operation at said focusing drive stage.

14. The focus adjusting method according to claim 1, wherein said large focus area is defined by an AF frame formed at a position corresponding to a center of a picture plane.

15. The focus adjusting method according to claim 1, wherein said large focus area comprises a central large focus area and two side focus areas positioned on opposite sides of said central large focus areas, respectively,

wherein said central large focus area is defined by a spot AF frame, and

wherein a combination of said central large focus area and said two side focus areas are defined by a multi-zone AF frame which is greater in width than said spot AF frame.

16. A focus adjusting device comprising:

a lens driving device for moving a focusing lens group of a photographing optical system stepwise in a range of movement from one toward the other of a near extremity and a far extremity;

an image pickup device for capturing an image formed by said photographing optical system; and

a controller which performs a focus search stage in which said image pickup device is activated to capture an object image at each of a plurality of different positions of said focusing lens group while said focusing lens group is moved stepwise from one toward the other of a near extremity and a far extremity to obtain an in-focus state based on a contrast of an image formed by said photographing optical system in one of at least one large focus area and each of a plurality of small focus areas included in said large focus area.