JP2007241008A - Automatic focusing device and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focusing device capable of moving a focus lens to a focusing position precisely. <P>SOLUTION: By performing initial position return operations 1 and 2, the focus lens is driven in the same direction (infinity direction) such that a moving start position assigned to a focusing position search drive operation and a moving start position assigned to a focusing drive operation coincide (at the proximity end), and then the lens position is measured having the coinciding position as a reference position. In addition, when the focus lens comes into contact with the proximity end and stops by the initial position return operations 1 and 2, control is exerted so that the speed at which the focus lens comes into the proximity end may have a constant prescribed speed V1. Consequently, amounts of backlash that may occur during positioning at the proximity end can be made almost equal. Accordingly, the focus lens can be precisely positioned at a peak position when the focusing operation takes places. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a contrast AF type autofocus device and a camera equipped with the autofocus device.

  In contrast AF cameras, for example, by moving the focus lens from the infinity side to the closest side, the focus evaluation value is acquired in small increments, and the focus lens is moved to the lens position where the focus evaluation value reaches its peak. AF is performed (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-142488

  By the way, when moving to the peak lens position, the lens driving direction is reversed. However, there is a problem in that it cannot be accurately moved to the peak position due to mechanical backlash of the drive system that occurs during the reverse rotation driving.

The invention according to claim 1 is applied to an autofocus device that performs a focusing operation by a contrast AF method based on an imaging signal, and a first control unit that causes a focus lens to reach a predetermined position at a predetermined speed, and a predetermined focus lens. Calculating means for calculating the in-focus position based on the imaging signal by moving from the position; second control means for causing the focus lens to reach the predetermined position at a predetermined speed after the calculation of the in-focus position by the calculating means; Focusing means for moving the focus lens from a predetermined position to a focusing position and performing a focusing operation after the control by the control means is provided.
According to a second aspect of the present invention, in the autofocus device that performs the focusing operation by the contrast AF method based on the imaging signal, the first control means for causing the focus lens to reach a predetermined position, and the focus lens by the first control means. Storage means for storing the speed when reaching the predetermined position, calculation means for moving the focus lens from the predetermined position to calculate a focus position based on the imaging signal, and focus calculation after calculation of the focus position by the calculation means A second control means for causing the lens to reach a predetermined position at a speed stored in the storage means; and after the control by the second control means, the focus lens is moved from the predetermined position to the in-focus position to perform a focusing operation. And a focusing means for adjusting the position.
According to a third aspect of the present invention, in the autofocus device according to the first or second aspect, the movement of the focus lens is mechanically restricted by a restricting member and stopped at the predetermined position.
According to a fourth aspect of the present invention, in the autofocus device according to any one of the first to third aspects, the first and second control means determine the speed at which the focus lens reaches the predetermined position. Is controlled to be equal to or less than the upper limit speed at which the correlation between the positioning error amount and the arrival speed when the speed reaches is maintained.
According to a fifth aspect of the present invention, a camera includes the autofocus device according to any one of the first to fourth aspects.

  According to the present invention, the focus lens movement start position at the time of calculating the focus position and the focus lens movement start position at the time of moving the focus lens to the focus position are the same predetermined position. Since the speed at which the focus lens reaches the position is also the same, the focus lens can be accurately moved to the calculated in-focus position.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a camera equipped with an autofocus device according to the present invention, and is a block diagram showing a schematic configuration of the camera. The camera shown in FIG. 1 is an interchangeable lens type camera, and a lens barrel 200 is attached to a camera body 100. Reference numeral 300 denotes a control device provided in the camera body 100. Note that the present invention can be applied not only to an interchangeable lens camera but also to a lens-integrated camera.

  The lens barrel 200 is provided with lenses 210 a to 210 d and a diaphragm 250. The lens 210b is a zoom lens for adjusting the focal length. When the zoom ring (not shown) is manually operated, the zoom lens 210b moves in the optical axis direction, and the focal length of the entire optical system changes. The position of the zoom lens 210b is detected by the zoom encoder 220. The lens 210 c is a focus lens for focus adjustment, and is driven in the optical axis direction by the drive motor 240. The drive motor 240 is controlled by a drive signal from the lens drive control unit 140. The lens position of the focus lens 210c is detected by the distance encoder 230.

  An imaging device 110 is provided in the camera body 100, and subject images are formed on the imaging surface by lenses 210a to 210d. The imaging device 110 is provided with an imaging element that is a photoelectric conversion element, an infrared cut filter, an optical low-pass filter, and the like. A CCD image sensor, a CMOS sensor, a CID, or the like is used as the image sensor.

  The control device 300 includes an evaluation value calculation unit 120, a lens target position setting unit 130, a lens drive control unit 140, and a storage unit 170. The control device 300 is connected to a half-press switch 150 that is turned on by a half-press operation of a release button provided in the camera, and a full-press switch 160 that is turned on by a full-press operation of the release button. The storage unit 170 stores data such as a focus evaluation value.

  An imaging signal is input from the imaging device 110 to the evaluation value calculation unit 120. The evaluation value calculation unit 120 calculates a focus evaluation value based on the imaging signal of the portion corresponding to the set AF area. As a method for calculating the focus evaluation value, a focus evaluation value is obtained by performing filter processing (mainly high frequency emphasis filter processing) on the imaging signal and integrating them.

  The lens target position setting unit 130 sets a target position when driving the focus lens 210 c with the drive motor 240. For example, in the contrast AF method using the focus evaluation value, the focus lens 210c is moved by a predetermined amount, the focus evaluation value is acquired to find the peak, and when the peak is detected, the focus lens 210c is moved to the peak position. Moving. In that case, the lens target position setting unit 130 sets the lens position ahead by a predetermined amount as the target position until the peak of the focus evaluation value is detected, and the peak position is the target when performing the focusing operation after the peak detection. Position.

<Explanation of lens driving operation>
Next, the lens driving operation during the AF operation will be described with reference to FIGS. FIG. 2 is a diagram showing an evaluation value curve L1 representing the relationship between the focus evaluation value and the lens position of the focus lens 210c, and the lens movement operation from the AF start until the focus lens 210c is driven to the peak position. The close end and the infinite end mechanically limit the movable range of the focus lens 210c, the close end is in a state where the closest subject is in focus, and the infinite end is in focus at an infinite subject. Is in the correct state.

  In the present embodiment, there are four types of lens movement operations from the start of AF until the focus lens 210c is driven to the peak position, that is, the initial position return operation 1, the focus position search drive operation, the initial position return operation 2, The focus driving operation is performed in order. In the focus position search drive operation, a so-called hill-climbing search operation is performed. In the present embodiment, the initial position in the initial position return operations 1 and 2 is set as the closest end, but it may be an infinite end or a lens position end closer to the lens position at the start of AF (closest end or Infinite end).

  In the AF operation by the conventional hill-climbing search, the focus position search driving operation is started from the lens position x1 to the infinite direction, and the calculation is performed if the lens position x2 exceeds the peak position xp at which the focus evaluation value is maximum. The focusing operation is completed by reversing the focus lens 120c by the driving amount (x2-xp). However, as described above, when the inversion drive is performed, the drive system generates a backlash, and the backlash amount cannot be predicted. Therefore, a deviation occurs between the calculated drive amount (x2-xp) and the actual drive amount. There is a problem that the peak position xp cannot be accurately positioned.

  Therefore, in the present embodiment, by performing the initial position return operations 1 and 2, the movement start position during the in-focus position search driving operation and the movement start position during the in-focus driving operation are the same position (closest end). Are driven in the same direction (infinite direction), and the lens position is measured with the same position as a reference position. Further, when the initial position return operations 1 and 2 come into contact with the closest end and come to rest, the drive control amount of the drive motor 240 is controlled so that the contact speed becomes the same predetermined speed V1.

  FIG. 5 shows the relationship between the lens driving speed at the time of contacting the closest end and the amount of play that occurs, and there is a correlation between the speed and the amount of play in a region where the lens driving speed is low. In the region where the speed exceeds the predetermined speed vth, no correlation is found between the speed and the backlash amount, and the backlash amount becomes indefinite. Therefore, by setting the contact speed during the initial position return operations 1 and 2 to the same speed V1 as described above, the amount of play when positioned at the closest end can be made substantially the same. For this reason, the movement start position of the in-focus position search drive operation and the movement start position of the in-focus operation are almost the same position, and the amount of error due to backlash included in the peak position measured by the in-focus position search drive operation and the in-focus position are determined. The amount of error due to backlash included in the drive amount measured during operation is substantially the same. As a result, the focus lens 120c can be accurately positioned at the peak position.

  FIG. 3 is a flowchart showing the operation procedure of the AF operation, and the program of the flowchart starts when the half-press switch 150 is turned on. In step S1, data and flags necessary for AF processing are initialized. For example, the initial value of the focus evaluation value stored in the storage unit 170 is set to zero. In step S2, the initial position return operation 1 of FIG. 2 is performed. That is, the focus lens 210c is moved from the lens position x1 in FIG. 2 toward the closest end and brought into contact with the close end, and the focus lens 210c is positioned at the close end that is the initial position. At this time, it is brought into contact with the closest end at the speed V1.

  The process from step S3 to step S5 in FIG. 3 is a process corresponding to the focus position search drive operation described above. In step S3, an in-focus evaluation value at the current lens position is acquired. The acquired focus evaluation value is stored in the storage unit 170. In step S4, it is determined whether or not the focus evaluation value acquired in step S3 is smaller than the previous focus evaluation value stored in the storage unit 170.

  Note that when the focus position search drive is performed (time t1 in FIG. 4), zero is stored in the storage unit 10 as the initial value of the previous focus evaluation value, so that it decreases when the process of step S4 is performed for the first time. It is determined that it is not. If it is determined that it is not decreasing, the process proceeds to step S5, and if it is determined that it is decreasing, the process proceeds to step S6.

  When the process proceeds from step S4 to step S5, the focus lens 210c is accelerated and decelerated between times t1 and t2 in FIG. 4 and driven by a predetermined drive amount Δx (see FIG. 2) in an infinite direction. In step S4, the focus evaluation value is acquired again. The processing of step S3 to step S5 is repeatedly executed until it is determined in step S4 that the decrease has occurred. As a result, as shown in FIG. 2, the focus lens 120c is step-driven in the direction in which the focus evaluation value increases.

  As shown in FIG. 2, when the lens position x2 passes the peak position xp, the focus evaluation value is decreased from the previous time, and is determined to be decreased in step S4, and the process proceeds to step S6. In step S6, the peak position is calculated based on the focus evaluation value detected by the focus position search drive operation. The peak position calculation method will be described later.

  In step S7, an initial position return operation 2 is performed, and the focus lens 120c is driven from the lens position x2 to the closest end (see FIG. 2). Also in this case, as in the case of the initial position return operation 1, the speed at the time of contacting the closest end is set to the predetermined speed V1. In step S8, a focus drive operation for moving the focus lens 120c to the calculated peak position is performed, and the series of focus operations is terminated. Thereafter, when the full push switch 160 is turned on, a photographing operation is executed.

  FIG. 4 shows the lens driving speed of the focus lens 210c during the AF operation. The vertical axis represents the lens driving speed, and the horizontal axis represents time. Here, the speed when moving in the infinite direction is positive, and the speed when moving in the closest direction is negative. From time zero to time t1, initial position return operation 1 is performed, from time t1 to t3 is focus position search drive operation, from time t3 to t4 is initial position return operation 2, and from time t4 to t5 is focus drive operation. Show. Further, the control operation from time t1 to t2 corresponds to the movement operation of Δx in FIG. 2, and the same control operation is repeated as many times as the number of repetitions of steps S3 to S5.

  In the initial position return operation 1, after the lens moving speed is accelerated to a predetermined speed V1, the speed is held at V1, and as shown by the symbol A, the lens is brought into contact with the closest end and positioned. Also, in the initial position return operation 2, the same speed control as in the initial position return operation 1 is performed, and the focus lens 120c is brought into contact with the closest end at a speed V1 as indicated by reference numeral B. As described above, the measurement reference position (closest end) at the time of peak calculation and the drive start reference position (closest end) at the time of in-focus driving are almost the same, so positioning accuracy to the peak position by the focusing operation Can be improved.

[Calculation method of peak position]
FIG. 6 is a diagram for explaining a method for calculating a focus lens position. Here, a three-point interpolation operation will be described. The black circles shown in FIG. 6 indicate the focus evaluation value sampling points, and are acquired in the order of S1, S2, and S3. When the sampling point S3 is acquired, the focus evaluation value at the sampling point S3 has decreased with respect to the focus evaluation value at the sampling point S2, so that the process proceeds from step S4 to step S6 in FIG. 3 to calculate the peak position. .

  In the three-point interpolation calculation, the peak position xp is calculated using the sampling points S1, S2, and S3. First, a straight line L11 passing through the points S1 and S2 is calculated. When the slope of the straight line L11 is K, a straight line L12 passing through the point S3 with a slope of −K is calculated. The lens position at the intersection of the straight line L11 and the straight line L12 is defined as a peak position xp.

[Modification 1]
FIG. 7A is a diagram illustrating a first modification of lens drive control. In the initial position return operation 1, the lens driving speed is accelerated to V2 (> V1), and then decelerated from V2 to V1, and brought into contact with the closest end at the speed V1. The initial position return operation 2 performs the same control. By performing such control, the time required for the initial position return operations 1 and 2 can be shortened. On the other hand, in the drive control of FIG. 7A, when the required time is controlled to be the same as in the above-described embodiment, the contact speed can be set to V3 lower than V1, and at the same speed. Variation in the amount of play can be suppressed. As a result, the positioning accuracy can be further increased.

  FIG. 7B is a diagram showing a second modification of lens drive control. First, the return operation is performed at a high speed (for example, at the highest speed of the drive motor) and brought into contact with the closest end. Then, move it slightly in the infinite direction. Then, it is brought into contact with the closest end at a predetermined speed V1. The initial position return operation 2 performs the same control. In this way, the time required for the return operations 1 and 2 can be shortened by first returning to the closest end at the maximum speed. Since the second contact is performed at the predetermined speed V1, the backlash amount can be made substantially the same, and the first operation does not affect the positioning accuracy at the time of focusing.

  Further, in the above-described embodiment, the abutting speed is brought into contact with the closest end at a predetermined speed V1 set in advance. However, the abutting speed of the initial position return operation 1 is stored, and the initial position return operation 2 is stored. You may make it contact | abut to a near end at the made speed. For example, if the lens driving speed is brought into contact with the closest end during acceleration, if the contact speed of the initial position return operation 2 is set to the predetermined speed V1 as described above, the initial position return operation 1 and 2 are performed between the initial position return operations 1 and 2. The contact speed will be different, causing inconvenience. However, by using the contact speed stored in the initial position return operation 1 for the initial position return operation 2, the same speed can be obtained.

The operational effects of the present embodiment described above are summarized as follows.
(1) Control means (lens drive control unit 140) for causing the focus lens 120c to reach a predetermined position (closest end) at a predetermined speed in an autofocus device that performs a focusing operation by a contrast AF method based on an imaging signal; Means (control device 300) for calculating the focus position based on the imaging signal by moving the focus lens 120c from a predetermined position (closest end), and after calculating the focus position, the focus lens 120c is moved to the predetermined position (closest end). ) At a predetermined speed V1 (lens drive controller 140) and focusing means (lens drive controller 140) for moving the focus lens 20c from a predetermined position to the in-focus position to perform a focusing operation. Therefore, the positioning accuracy of the focus lens 120c at the in-focus position can be improved.
(2) The storage unit 170 stores the speed when the focus lens 120c first reaches the predetermined position, and the storage unit 140 stores the speed when the focus lens 120c reaches the predetermined position for the second time. The speed may be set, and the same effect can be obtained.
(3) Further, by controlling the speed at which the focus lens reaches the predetermined position to be equal to or less than the upper limit speed Vth at which the correlation between the positioning error amount and the arrival speed when the focus lens reaches the predetermined position is maintained. Highly accurate positioning is possible.

  In the embodiment described above, the case where the focus position search drive operation is a hill-climbing search operation has been described as an example. It can be similarly applied to. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

1 is a block diagram illustrating a schematic configuration of a camera, showing an embodiment of a camera including an autofocus device according to the present invention. It is a figure which shows the evaluation value curve L1 and the lens movement operation | movement at the time of AF operation | movement. It is a flowchart which shows the operation | movement procedure of AF operation | movement. It is a figure explaining the lens drive speed in AF operation | movement. It is a figure explaining the relationship between the lens drive speed at the time of contact | abutting to a near end, and play. It is a figure explaining the calculation method of a focusing lens position. It is a figure which shows a modification, (a) shows a 1st modification, (b) shows a 2nd modification, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 110: Imaging device 120: Evaluation value calculating part 130: Lens drive control part 140: Lens target position setting part 200: Lens barrel 300: Control apparatus 210a-210d: Lens 220: Zoom encoder 230: Distance encoder 240: Drive motor 250 : Aperture

Claims (5)

In an autofocus device that performs a focusing operation by a contrast AF method based on an imaging signal,
First control means for causing the focus lens to reach a predetermined position at a predetermined speed;
Arithmetic means for moving the focus lens from the predetermined position to calculate a focus position based on an imaging signal;
Second control means for causing the focus lens to reach the predetermined position at the predetermined speed after the calculation of the in-focus position by the arithmetic means;
An autofocus apparatus comprising: a focusing unit that moves the focus lens from the predetermined position to the focusing position after the control by the second control unit to perform a focusing operation. In an autofocus device that performs a focusing operation by a contrast AF method based on an imaging signal,
First control means for causing the focus lens to reach a predetermined position;
Storage means for storing a speed when the focus lens reaches the predetermined position by the first control means;
Arithmetic means for moving the focus lens from the predetermined position to calculate a focus position based on an imaging signal;
Second control means for causing the focus lens to reach the predetermined position at a speed stored in the storage means after calculation of the in-focus position by the calculation means;
An autofocus apparatus comprising: a focusing unit that drives the focus lens from the predetermined position to the in-focus position after the control by the second control unit to perform a focusing operation. The autofocus device according to claim 1 or 2,
An autofocus device characterized in that the movement of the focus lens is mechanically restricted by a restricting member and stopped at the predetermined position. In the autofocus device according to any one of claims 1 to 3,
The first and second control means maintain the correlation between the speed when the focus lens reaches the predetermined position and the positioning error amount when the focus lens reaches the predetermined position and the arrival speed. An autofocus device that is controlled below an upper limit speed.   A camera comprising the autofocus device according to any one of claims 1 to 4.

Images