Automatic focusing device
First Claim
Patent Images
1. An automatic focusing device, comprising:
- a lens that is movable along an optical axis thereof;
means for driving said lens;
means for obtaining a defocus amount of said lens with respect to a photographing object to obtain a distance measurement;
means for controlling said obtaining means to repeat distance measurements during a predetermined time interval;
means for determining a value representing a release-time-lag that occurs between a first event and a second event;
means for determining an integration time to obtain said defocus amount;
means for computing a relative speed of movement of said photographing object with respect to said lens along said optical axis, based upon a comparison of successive defocus amounts obtained by said obtaining means;
means for initiating a predictive focusing mode when said distance measurements indicate that a relative distance between said lens and said photographing object is decreasing; and
means for controlling said driving means in said predictive focusing mode to drive said lens, based upon computational results by said computing means, to a position where an in-focus condition is obtainable, said release-time-lag being modified when said predictive focusing mode is initiated by subtracting half said integration time from said release-time-lag, so that said lens is driven to said in-focus condition by an amount obtained by multiplying said relative speed of movement of said photographing object by said modified release-time-lag.
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Abstract
An automatic focusing device, in which a focus lens is driven by tracking an object-in-motion to obtain an in-focus state, based upon a focus prediction that is executed from repeated distance measurements. The amount of the lens drive for tracking is computed by taking the time required for integrating the distance measurements into account.
64 Citations
18 Claims
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1. An automatic focusing device, comprising:
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a lens that is movable along an optical axis thereof; means for driving said lens; means for obtaining a defocus amount of said lens with respect to a photographing object to obtain a distance measurement; means for controlling said obtaining means to repeat distance measurements during a predetermined time interval; means for determining a value representing a release-time-lag that occurs between a first event and a second event; means for determining an integration time to obtain said defocus amount; means for computing a relative speed of movement of said photographing object with respect to said lens along said optical axis, based upon a comparison of successive defocus amounts obtained by said obtaining means; means for initiating a predictive focusing mode when said distance measurements indicate that a relative distance between said lens and said photographing object is decreasing; and means for controlling said driving means in said predictive focusing mode to drive said lens, based upon computational results by said computing means, to a position where an in-focus condition is obtainable, said release-time-lag being modified when said predictive focusing mode is initiated by subtracting half said integration time from said release-time-lag, so that said lens is driven to said in-focus condition by an amount obtained by multiplying said relative speed of movement of said photographing object by said modified release-time-lag. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An automatic focusing device, comprising:
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a lens that is movable along an optical axis thereof; a motor that drives said lens; a detector that obtains a plurality of defocus amounts of a moving object during a predetermined time interval to obtain a plurality of distance measurements; means for determining a value representing a release-time-lag that occurs between a start of a shutter operation and a start of an exposure; means for determining an integration time to obtain each of said plurality of defocus amounts; a processor that computes a relative speed of movement of said moving object along said optical axis based upon a comparison of successive defocus amounts obtained by said detector; and means for initiating a predictive focusing mode when said distance measurements indicate that said moving object is approaching said lens, said motor being controlled in said predictive focusing mode to drive said lens based upon computational results by said processor to a position where an in-focus condition is obtainable, said release-time-lag, so that said lens is driven to said in-focus condition by an amount obtained by multiplying said relative speed of movement of said moving object by said modified release-time-lag. - View Dependent Claims (11, 12)
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13. A camera having an automatic focusing device, comprising:
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a lens that is movable along an optical axis thereof; a motor that drives said lens; a detector that obtains a plurality of defocus amounts of an object during a predetermined time interval to obtain a plurality of distance measurements; means for determining a value representing a release-time-lag that occurs between a start of a shutter operation and a start of an exposure; means for determining an integration time to obtain each of said plurality of defocus amounts; and a processor that computes a speed of movement with respect to said camera and said object, in which at least one of said camera and said object is moving, a predictive focusing mode being initiated when said distance measurements indicate that said moving object is approaching said lens, that causes said motor to drive said lens to an in-focus position, said release-time-lag being modified when said predictive focusing mode is initiated by subtracting half said integration time from said release-time-lag, so that said lens is driven to said in-focus position by an amount obtained by multiplying said speed of movement by said modified release-time-lag. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification