Focus detection method and focus detection apparatus

• US 20060078323A1
• Filed: 10/07/2005
• Published: 04/13/2006
• Est. Priority Date: 10/07/2004
• Status: Active Grant

• Current Assignee: PENTAX RICOH IMAGING COMPANY, LTD.
• Original Assignee: Pentax Corporation (Hoya Corporation)
• Inventors: Nakahara, Naoto
• Granted Patent: US 7,526,192 B2
• Time in Patent Office: Days
• US Class Current: 396/127
• CPC Class Codes: G03B 13/36 Autofocus systems
• CPC Class Codes: H04N 2101/00 Still video cameras
• CPC Class Codes: H04N 23/10 for generating image signals from different wavelengths
• CPC Class Codes: H04N 23/12 with one sensor only
• 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 25/134 based on three different wavelength filter elements

Abstract

A focus detection method, for detecting a focus state of an object image in accordance with a contrast of the object image which is formed in a focus detection area, includes capturing the object images while moving a focusing lens group of a photographing lens stepwise within a predetermined range of movement thereof; determining contrast values of the plurality of object images in the focus detection area; and setting a position of the focusing lens group as an in-focus position when a contrast value, attained when the focusing lens group is positioned at one of the closest focus position and the infinite-focus position or at a position within a predetermined range of steps from the one of the closest focus position and the infinite-focus position toward the other of the closest focus position and the infinite-focus position, is at a maximum contrast value.

Claims

1. A focus detection method for detecting a focus state of an object image in accordance with a contrast of said object image which is formed in a focus detection area, said focus detection method comprising:

capturing a plurality of said object images while moving a focusing lens group of a photographing lens stepwise within a predetermined range of movement of said focusing lens group;

determining contrast values of said plurality of object images in said focus detection area; and

setting a position of said focusing lens group as an in-focus position when a contrast value, attained when said focusing lens group is positioned at one of the closest focus position and the infinite-focus position or at a position within a predetermined range of steps from said one of the closest focus position and the infinite-focus position toward the other of the closest focus position and the infinite-focus position, is at a maximum contrast value.

2. The focus detection method according to claim 1, further comprising:

determining whether or not a contrast value among said contrast values of said plurality of object images, which are determined when said focusing lens group is moved stepwise in a predetermined direction, is a peak contrast value, wherein said contrast values increase a first predetermined number of times consecutively and subsequently decrease a second predetermined number of times consecutively,

wherein in the case where said peak contrast value is not detected, said focusing lens group is moved to said focusing lens group position determined when said contrast value, attained when said focusing lens group is positioned at one of the closest focus position and the infinite-focus position or at a position within a predetermined range of steps from said one of the closest focus position and the infinite-focus position toward the other of the closest focus position and the infinite-focus position, is at a maximum contrast value.

3. The focus detection method according to claim 2, wherein said peak contrast value determining step includes detecting whether or not a contrast value among said contrast values of said plurality of object images, which are determined when said focusing lens group is moved stepwise in a predetermined direction, is a peak contrast value wherein said contrast values increase a first predetermined number of times consecutively and subsequently decrease a second predetermined number of times consecutively.

4. The focus detection method according to claim 3, wherein when determining whether or not said peak contrast value exists during movement of said focusing lens group from said closest focusing position to an infinite focusing position, further comprising:

determining whether any of said contrast values determined at said closest focusing position and a position a predetermined distance away from said closest focusing position toward said infinite focus position corresponding to an amount less than said first predetermined number of times is said maximum contrast value when no said peak contrast value can be determined.

5. The focus detection method according to claim 3, wherein when determining whether or not said peak contrast value exists during movement of said focusing lens group from an infinite focusing position to said closest focusing position, said focus detection method further comprises:

determining whether any of said contrast values determined at said closest focusing position and a position a predetermined distance away from said closest focusing position toward said infinite focus position corresponding to an amount less than said first predetermined number of times is said maximum contrast value when no said peak contrast value can be determined.

6. The focus detection method according to claim 4, wherein in the case where said first predetermined number of times is two, said focusing detection method further comprises:

determining that said maximum contrast value is valid when determining that said any of said contrast values is said maximum contrast value if a ratio between said maximum contrast value and a contrast value determined at a position of said focusing lens group two steps away from said closest focusing position toward said infinite focus position is smaller than a predetermined value.

7. The focus detection method according to claim 5, wherein in the case where said first predetermined number of times is two, said focusing detection method further comprises:

determining that said maximum contrast value is valid when determining that said any of said contrast values is said maximum contrast value if a ratio between said maximum contrast value and a contrast value, determined at a position of said focusing lens group two steps away from said focusing lens group position at which said maximum contrast value is attained toward said closest focus position, is smaller than a predetermined value.

8. The focus detection method according to claim 2, further comprising:

visually indicating that an in-focus state is not achieved when moving said focusing lens group to said position at which said maximum contrast value is determined.

9. The focus detection method according to claim 8, further comprising:

visually indicating that an in-focus state is achieved if determining said maximum contrast value at a position of said focusing lens group closer to said infinite focus position than said closest focusing position and if determining that said maximum contrast value is valid.

10. The focus detection method according to claim 1, wherein said focus detection area is selected from a plurality of focus detection areas.

11. The focus detection method according to claim 8, wherein an out-of-focus state is visually indicated by a light emitter in the case where an in-focus state is not achieved.

12. The focus detection method according to claim 8, wherein an out-of-focus state is visually indicated on a display device in the case where an in-focus state is not achieved.

13. The focus detection method according to claim 1, wherein said contrast values of said object image are measured via an image pickup device.

14. A focus detection method for detecting a focus state of an object image in accordance with a contrast of said object image which is formed in a focus detection area, said focus detection method comprising:

capturing a plurality of said object images while moving a focusing lens group of a photographing lens stepwise within a predetermined range of movement of said focusing lens group;

determining contrast values of said plurality of object images in said focus detection area;

determining whether or not a contrast value among said contrast values of said plurality of object images, which are determined when said focusing lens group is moved stepwise in a predetermined direction, is a peak contrast value wherein said contrast values increase a first predetermined number of times consecutively and subsequently decrease a second predetermined number of times consecutively; and

moving said focusing lens group to a position thereof in which said maximum contrast value is determined if it is determined that said contrast value among said contrast values, which is determined when said focusing lens group is located said one of at said closest focusing position and in the close vicinity thereof, is said maximum contrast value, in the case where said peak contrast value is not detected.

15. A focus detection apparatus for detecting a focus state of an object image in accordance with a contrast of said object image which is formed in a focus detection area, said focus detection apparatus comprising:

a lens drive mechanism for moving a focusing lens group of a photographing lens system within a predetermined range of movement;

an image-capturing device for capturing a plurality of said object images while moving said focusing lens group of a photographing lens stepwise within a predetermined range of movement of said focusing lens group;

a contrast value determining device for determining a plurality of contrast values of said plurality of object images in said focus detection area; and

a controller for detecting whether or not a contrast value among said contrast values of said plurality of object images, which are determined when said focusing lens group is moved stepwise in a predetermined direction, is a peak contrast value;

wherein, if said peak contrast value is not detected, said controller moves said focusing lens group to a position thereof in which a maximum contrast value is determined if it is determined that a contrast value among said plurality of contrast values, which is determined when said focusing lens group is located said one of at said closest focusing position and in the close vicinity thereof, is said maximum contrast value.