JP2016142998A - FOCUS ADJUSTMENT DEVICE, IMAGING DEVICE, FOCUS ADJUSTMENT DEVICE CONTROL METHOD, AND PROGRAM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for minimizing reduction in speed and accuracy of focus adjustment made using a hybrid AF method.SOLUTION: A focus adjustment unit includes focus adjustment means for adjusting focus by moving a focus adjustment member to be focused on an object, and switching means configured to switch a focus adjustment method used by the focus adjustment means, while performing focus adjustment, between a phase-difference-based method based on phase difference between a pair of object images and a contrast-based method based on contrast of an object image. When the switching means switches the method from the phase-difference-based method to the contrast-based method, the focus adjustment means moves the focus adjustment member by a predetermined distance in a first direction, which is the same as a movement direction before the switching, and then moves the focus adjustment member, from a position after the movement, in a second direction opposite the first direction to perform focus adjustment using the contrast-based method.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a focus adjustment apparatus, an imaging apparatus, a control method for the focus adjustment apparatus, and a program.

  As a general AF method for adjusting the focus of the imaging apparatus, there are a contrast AF method and a phase difference AF method. The contrast AF method is an AF method often used in video cameras and digital still cameras, and an image sensor is used as a focus detection sensor. The contrast AF method is an AF method that focuses on the output signal of the image sensor, particularly the contrast information of the high frequency component, and uses the position of the focus lens where the AF evaluation value is the largest as the in-focus position. However, in the contrast AF method, the AF evaluation value is obtained while moving the position of the focus lens in the optical axis direction by a very small amount, as it is also called a hill-climbing method, and until the AF evaluation value is found to be maximum as a result. It is necessary to move the focus lens. Therefore, the contrast AF method is not suitable for high-speed focus detection operation.

  On the other hand, the phase difference AF method is an AF method often used for single-lens reflex cameras. For example, in a digital single-lens reflex camera, phase difference detection is performed by a focus detection unit including a secondary imaging optical system. The focus detection unit includes a pupil division unit that divides the light beam that has passed through the exit pupil of the photographing optical system into two regions, and the divided light beam is second-order through an optical path division unit disposed in the mirror box. An image is formed on a set of focus detection sensors by an imaging optical system. Then, by detecting the shift amount of the signal output according to the received light amount of the focus detection sensor, that is, the relative positional shift amount in the pupil division direction, the shift amount in the focus direction of the photographing optical system is directly determined. Ask. Therefore, once the accumulation operation is performed by the focus detection sensor, the amount and direction of the focus shift can be obtained at the same time, and a high-speed focus adjustment operation can be performed. At the time of photographing after focus detection, the optical path dividing means is retracted out of the photographing light beam, and the image sensor is exposed to photograph an image.

  A phase difference AF method (imaging surface phase difference AF method) using an image sensor is also known. In the imaging surface phase difference AF method, an imaging pixel in an imaging element is divided into pupils by a microlens to be a focus detection pixel. A plurality of focus detection pixels receive the light flux to perform focus detection at the same time as imaging.

  Patent Document 1 discloses a technique in which each photodiode receives light from a different pupil plane of an imaging lens by dividing photodiodes collected by one microlens in one pixel. Is disclosed. This makes it possible to detect the imaging surface phase difference by comparing the outputs of the two photodiodes.

  Patent Document 2 discloses a technique for providing a pupil division function by decentering a sensitivity region of a light receiving unit with respect to an optical axis of an on-chip microlens in some light receiving pixels of an image sensor. These pixels are used as focus detection pixels, and are arranged at predetermined intervals between the photographing pixel groups, thereby performing imaging surface phase difference detection. Here, since the location where the focus detection pixels are arranged corresponds to a missing portion of the imaging pixel, image information is generated by interpolating from the surrounding imaging pixel information for this location. In the imaging surface phase difference AF method, since the phase difference can be detected on the imaging surface, high-speed and high-precision focus adjustment can be performed even when observing an electronic viewfinder or shooting a moving image.

  Patent Document 3 discloses a hybrid AF method as an AF method that enables high-speed and high-precision focus adjustment by taking advantage of the mutual advantages of the imaging surface phase difference AF method and the contrast AF method.

JP 2001-083407 A JP 2009-003122 A JP 2013-254166 A

  Consider a case where the imaging AF phase difference AF method is switched to the contrast AF method in the hybrid AF method. In this case, the movement start position (scan start position) and movement direction (scan direction) of the focus lens in the contrast AF after the switching affect the speed and accuracy of focus adjustment. Depending on the scan start position and the scan direction, it may be necessary to scan a wide range until the focus lens position (peak position) at which the AF evaluation value is maximum is finally detected, and the speed and accuracy of focus adjustment are reduced. there is a possibility. As a result, the time when the subject is not in focus lasts for a long time. For example, in the case of moving image shooting, the image quality of the moving image may deteriorate.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for suppressing a decrease in the speed and accuracy of focus adjustment by the hybrid AF method.

  In order to solve the above-described problem, the present invention uses a focus adjustment unit that performs focus adjustment so that a subject is focused by moving a focus adjustment member, and the focus adjustment unit uses the focus adjustment unit between the focus adjustments. Switching means for switching the focus adjustment method from a phase difference method based on the phase difference of a pair of subject images to a contrast method based on the contrast of the subject image, and switching from the phase difference method to the contrast method by the switching means. When the movement is performed, the focus adjustment unit moves the focus adjustment member by a predetermined distance in the same first direction as the movement direction before the switching, and is opposite to the first direction from the position after the movement. The focus adjustment apparatus is characterized in that the focus is adjusted by the contrast method by moving in the second direction.

  Other features of the present invention will become more apparent from the accompanying drawings and the following description of the preferred embodiments.

  According to the present invention, it is possible to suppress a reduction in focus adjustment speed and accuracy by the hybrid AF method.

The block diagram of the digital camera 150 which concerns on 1st and 2nd embodiment. 6 is a flowchart of a one-shot AF operation executed by the camera MPU 125 according to the first embodiment. The flowchart which shows the detail of hybrid AF control in S209 of FIG. 2, and S509 of FIG. The figure which shows the specific example of the hybrid AF control which concerns on 1st Embodiment. 10 is a flowchart for explaining hybrid AF control in a continuous AF operation performed by a camera MPU 125 according to the second embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The technical scope of the present invention is determined by the claims, and is not limited by the following individual embodiments. In addition, not all combinations of features described in the embodiments are essential to the present invention.

[First Embodiment]
An embodiment in which the focus adjustment device of the present invention is applied to a single-lens reflex type digital camera (imaging device) with interchangeable lenses will be described. FIG. 1 is a block diagram of a digital camera 150 according to the first embodiment. The digital camera 150 is an interchangeable lens type single-lens reflex camera, and includes a lens unit 100 and a camera body 120. The lens unit 100 is connected to the camera body 120 via a mount M indicated by a dotted line in the center of FIG.

  The digital camera 150 executes hybrid AF that combines phase difference focus adjustment (imaging surface phase difference AF) based on the phase difference between a pair of subject images acquired on the imaging surface and contrast focus adjustment (contrast AF). It is configured as possible. Since both imaging surface phase difference AF and contrast AF are based on information on the imaging surface, focus detection accuracy can be improved compared to combining phase difference AF and contrast AF on a non-imaging surface. However, the phase difference AF of the hybrid AF of the present embodiment is not limited to the imaging surface phase difference AF. In the following description, the imaging surface phase difference AF may be simply referred to as phase difference AF.

  The lens unit 100 includes a first lens group 101, a diaphragm / shutter 102, a second lens group 103, and a focus lens group (hereinafter simply referred to as “focus lens 104”). As described above, the lens unit 100 includes the focus lens 104 and includes a photographing optical system that forms an image of a subject.

  The first lens group 101 is disposed at the tip of the lens unit 100 and is held so as to be able to advance and retreat in the optical axis direction OA. The aperture / shutter 102 adjusts the aperture diameter to adjust the amount of light during shooting, and also functions as an exposure time adjustment shutter when shooting a still image. The aperture / shutter 102 and the second lens group 103 integrally move forward / backward in the optical axis direction OA, and realize a zoom function in conjunction with the forward / backward movement of the first lens group 101. The focus lens 104 performs focus adjustment by moving back and forth in the optical axis direction OA.

  The lens unit 100 also includes a zoom actuator 111, an aperture shutter actuator 112, a focus actuator 113, a zoom drive circuit 114, an aperture shutter drive circuit 115, and a focus drive circuit 116. Further, the lens unit 100 includes a lens MPU 117 and a lens memory 118.

  The zoom actuator 111 performs a zoom operation by driving the first lens group 101 and the second lens group 103 forward and backward in the optical axis direction OA. The aperture shutter actuator 112 controls the aperture diameter of the aperture / shutter 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. The focus actuator 113 performs focus adjustment by driving the focus lens 104 forward and backward in the optical axis direction OA. The focus actuator 113 has a position detection function for detecting the current position of the focus lens 104.

  The zoom drive circuit 114 drives the zoom actuator 111 according to the zoom operation of the photographer. The shutter drive circuit 115 controls the aperture of the diaphragm shutter 102 by drivingly controlling the diaphragm shutter actuator 112. The focus drive circuit 116 controls the focus actuator 113 based on the focus detection result, and performs focus adjustment by driving the focus lens 104 back and forth in the optical axis direction OA.

  The lens MPU 117 performs calculation and control related to a photographing optical system that forms a subject image on the image sensor 122, and controls the zoom driving circuit 114, the shutter driving circuit 115, the focus driving circuit 116, and the lens memory 118. The lens MPU 117 detects the current lens position, and notifies the lens position information in response to a request from the camera MPU 125. The lens memory 118 stores optical information necessary for automatic focus adjustment.

  The camera body 120 includes an optical low-pass filter 121 and an image sensor 122. The optical low-pass filter 121 reduces false colors and moire in the captured image. The image sensor 122 is composed of a C-MOS sensor and its peripheral circuit, and one photoelectric conversion element is arranged on light receiving pixels of m pixels in the horizontal direction and n pixels in the vertical direction. The image sensor 122 is configured to be able to output all pixels independently. Some pixels are focus detection pixels, and phase difference type focus detection is possible on the imaging surface.

  More specifically, the image sensor 122 has a plurality of photographing pixels that each receive a light beam passing through the entire exit pupil of the photographing optical system that forms an image of the subject and generate an image of the subject. The image sensor 122 further includes a plurality of focus detection pixels that each receive a light beam passing through different exit pupil regions of the imaging optical system. The plurality of focus detection pixels can receive a light beam passing through the entire exit pupil of the photographing optical system as a whole. For example, the imaging element 122 leaves a pair of G pixels arranged diagonally out of 2 × 2 pixels as imaging pixels, and replaces R and B pixels with focus detection pixels.

  In the present embodiment, phase detection method focus detection on the imaging surface is realized by replacing some of the photographing pixels with focus detection pixels, but the present invention is not limited to this method. For example, as in Patent Document 1, two photodiodes are held in one pixel, a light beam is separated by a microlens, and an image is formed by the two photodiodes. It may be a system in which a signal can be taken out.

  The camera body 120 also includes an image sensor driving circuit 123, an image processing circuit 124, a camera MPU 125, a display 126, an operation switch group 127, a memory 128, an imaging surface phase difference focus detection unit 129, and a TVAF focus detection unit 130.

  The image sensor drive circuit 123 controls the operation of the image sensor 122, A / D converts the acquired image signal, and transmits it to the camera MPU 125. The image processing circuit 124 performs γ conversion, color interpolation, JPEG compression, and the like of the image acquired by the image sensor 122.

  The camera MPU 125 performs calculation and control related to the camera body 120, and includes an image sensor driving circuit 123, an image processing circuit 124, a display 126, an operation switch group 127, a memory 128, an imaging surface phase difference focus detection unit 129, and a TVAF focus. The detection unit 130 is controlled.

  The camera MPU 125 is connected to the lens MPU 117 via the signal line of the mount M, acquires a lens position from the lens MPU 117, and issues a lens driving request with a predetermined driving amount to the lens MPU 117. The camera MPU 125 acquires optical information specific to the lens unit 100 from the lens MPU 117.

  The camera MPU 125 includes a ROM 125a that stores a program for controlling camera operations, a RAM 125b that stores variables, and an EEPROM 125c that stores various parameters. Further, the camera MPU 125 executes focus detection processing by a program stored in the ROM 125a. Details of the focus detection process will be described later. The camera MPU 125 also corrects the imaging plane phase difference AF because the influence of vignetting is large and the reliability decreases when the image height at the focus detection position is large.

  The display 126 includes an LCD or the like, and displays information related to the shooting mode of the camera body 120, a preview image before shooting and a confirmation image after shooting, a focus state display image at the time of focus detection, and the like. The operation switch group 127 includes a power switch, a release switch (focus adjustment operation trigger), a zoom operation switch, a shooting mode selection switch, and the like. The memory 128 of this embodiment is a detachable flash memory, and records captured images.

  The imaging surface phase difference focus detection unit 129 performs focus detection processing by a phase difference method based on image signals of focus detection pixels embedded in the image sensor 122. More specifically, the imaging surface phase difference focus detection unit 129 performs focus detection based on the shift amount of the pair of images formed on the focus detection pixels by the light beams passing through the pair of pupil regions of the imaging optical system. The evaluation value (phase difference focus evaluation value) is generated. The camera MPU 125 performs imaging plane phase difference AF based on the phase difference focus evaluation value generated by the imaging plane phase difference focus detection unit 129. The principle of the imaging plane phase difference AF is the same as that described in FIGS. 5 to 7 and FIG.

  The TVAF focus detection unit 130 performs a focus detection process by a contrast method using the contrast component of the image information obtained by the image processing circuit 124, and generates an evaluation value (contrast focus evaluation value). In the contrast type focus detection process, the focus lens 104 is moved to detect the position of the focus lens 104 at which the contrast focus evaluation value peaks.

  Hereinafter, the focus adjustment process executed by the camera MPU 125 will be described with reference to FIGS. FIG. 2 is a flowchart of a one-shot AF operation performed by the camera MPU 125. Unless otherwise specified, the processing of each step in this flowchart is realized by the camera MPU 125 executing a program stored in the ROM 125a using the RAM 125b as a work memory.

  In S200, the camera MPU 125 continuously performs a focus adjustment operation, and performs a continuous AF operation to prepare for the one-shot AF operation. Here, processes such as exposure to the image sensor 122, acquisition of a focus evaluation value used for imaging surface phase difference AF and contrast AF, and driving of the focus lens 104 are continuously performed, but detailed description thereof is omitted.

  In step S201, the camera MPU 125 determines whether the release switch of the operation switch group 127 has been pressed, that is, whether a focus adjustment operation trigger has been issued. If the release switch has not been pressed, the camera MPU 125 continues the continuous AF operation in S200. If the release switch has been pressed, the process proceeds to S202.

  In S202, the camera MPU 125 determines whether or not the latest phase difference focus evaluation value obtained from the imaging plane phase difference focus detection unit 129 during the continuous AF process in S200 is highly reliable. When the reliability is high, it is considered that this phase difference focus evaluation value can be used for the phase difference AF method. This reliability includes information on at least one of the matching degree and contrast of a pair of images obtained as a result of the imaging surface phase difference AF. If it is determined that the reliability is high, the process proceeds to S203; otherwise, the process proceeds to S204.

  In step S <b> 203, the camera MPU 125 calculates the drive amount of the focus lens 104 based on the image shift amount of the phase difference focus evaluation value (hereinafter referred to as “defocus amount”), and the focus lens via the focus drive circuit 116. 104 is driven.

  In step S204, the camera MPU 125 calculates a scan start position in preparation for a scan operation using the contrast AF method, and drives the focus lens 104 via the focus drive circuit 116 using the scan start position as a target position.

  In step S205, the camera MPU 125 switches the drive mode of the image sensor 122 to the high-speed frame rate mode in order to increase the speed of the one-shot AF operation. In step S206, the camera MPU 125 performs exposure control so that a focus evaluation value suitable for focus adjustment is obtained.

  In step S207, the camera MPU 125 waits until the focus lens 104 that has started driving in step S203 or S204 reaches the target position. When the focus lens 104 reaches the target position, the process proceeds to S208. In step S208, the camera MPU 125 waits until the focus evaluation value of the image exposed at the current focus lens position is output. When the focus evaluation value is output, the process proceeds to S209.

  In step S209, the camera MPU 125 performs hybrid AF control using the imaging surface phase difference AF method and the contrast AF method. The detailed description here will be described with reference to FIG. Thereby, the one-shot AF operation is completed.

  FIG. 3 is a flowchart showing details of the hybrid AF control in S209 of FIG. The process of this flowchart is performed every time one image is captured. Unless otherwise specified, the processing of each step in this flowchart is realized by the camera MPU 125 executing a program stored in the ROM 125a using the RAM 125b as a work memory.

  In step S300, the camera MPU 125 initializes a phase difference drive completion counter that represents the number of times of continuous drive of the focus lens 104 using a phase difference focus evaluation value described later. In step S301, the camera MPU 125 initializes a phase difference driving flag indicating that the focus lens 104 is being driven by a phase difference focus evaluation value described later.

  In step S <b> 302, the camera MPU 125 performs exposure on the image sensor 122. In step S <b> 303, the camera MPU 125 acquires a contrast focus evaluation value from the TVAF focus detection unit 130. In step S <b> 304, the camera MPU 125 acquires a phase difference focus evaluation value from the imaging surface phase difference focus detection unit 129.

  In step S305, the camera MPU 125 determines whether the phase difference drive completion counter is less than a preset threshold value. If the phase difference drive completion counter is less than the threshold value, the process proceeds to S306; otherwise, the process proceeds to S315. Although details will be described later, switching from the contrast AF method to the imaging surface phase difference AF method is performed in S310. Therefore, when the phase difference drive completion counter is equal to or greater than the threshold value, the process does not reach S310, and switching from the contrast AF method to the imaging surface phase difference AF method is prohibited. Thereby, frequent switching of the focus adjustment method (frequent state transition between the contrast AF method and the imaging plane phase difference AF method) can be avoided. Note that the threshold value here can be set to an appropriate value depending on the driving characteristics of the lens unit 100 (particularly, the driving characteristics of the focus lens 104), the AF mode, and the like. That is, the camera MPU 125 may change the threshold value of the phase difference drive completion counter according to the drive characteristics of the lens unit 100 and the like.

  In S306, the camera MPU 125 determines whether or not the phase difference focus evaluation value acquired from the imaging plane phase difference focus detection unit 129 in S304 is high (greater than or equal to a threshold value). When the reliability is high, it is considered that this phase difference focus evaluation value can be used for the phase difference AF method. This reliability includes information on at least one of the matching degree and contrast of a pair of images obtained as a result of the imaging surface phase difference AF. If it is determined that the reliability is high, the process proceeds to S307. If not (the reliability is less than the threshold value), the process proceeds to S312.

  In step S307, the camera MPU 125 determines whether the defocus amount of the phase difference focus evaluation value is within the depth of focus. If it is determined that the defocus amount is within the depth of focus, the camera MPU 125 determines that the subject can be focused and ends the hybrid AF control. If it is determined that the defocus amount is not within the depth of focus, the process proceeds to S310.

  In S310, the camera MPU 125 sets a phase difference driving flag. That is, when the process of S310 is performed during the execution of contrast AF (the phase difference driving flag is cleared), the contrast AF method is switched to the imaging surface phase difference AF method. In step S <b> 311, the camera MPU 125 calculates the drive amount of the focus lens 104 based on the defocus amount of the phase difference focus evaluation value, and drives the focus lens via the focus drive circuit 116. Thereafter, the process returns to S302.

  If it is determined in S306 that the reliability of the phase difference focus evaluation value is low, in S312, the camera MPU 125 determines whether the phase difference driving flag is set (that is, the camera MPU 125 operates in the imaging plane phase difference AF method). Or not). If the phase difference driving flag is set, the process proceeds to S313. Otherwise, the process proceeds to S315, and contrast AF is executed (that is, the camera MPU 125 continues to operate in the contrast AF method).

  In step S313, the camera MPU 125 increments the phase difference drive completion counter. By this processing, the number of times of shifting from the imaging surface phase difference AF method to the contrast AF method can be managed. In step S314, the camera MPU 125 clears the phase difference driving flag. That is, switching from the imaging surface phase difference AF method to the contrast AF method is performed by the process of S314.

  Subsequent to S314, in S331, the camera MPU 125 determines a scan start position in preparation for scan driving with contrast AF performed in S315 and later described. Details of the scan start position will be described later with reference to FIG. In step S <b> 332, the camera MPU 125 drives the focus lens 104 via the focus drive circuit 116 with the scan start position as a target position. In step S333, the camera MPU 125 sets the scan direction in the contrast AF to a direction (second direction) opposite to the moving direction (first direction) of the focus lens 104 in the immediately preceding imaging plane phase difference AF. Thereafter, the process proceeds to S315, and contrast AF is executed.

  The process of S315 is performed following the process of S305, S312 or S331. In step S315, the camera MPU 125 determines whether a peak of the contrast focus evaluation value has been detected. The detection of the peak is generally determined based on the rise and fall of the contrast focus evaluation value. However, the amount of fluctuation and the number of fluctuations of the contrast focus evaluation value are arbitrary, and the details here will be described. Description is omitted. If a peak is detected, the process proceeds to S316, and if not, the process proceeds to S319.

  In S316, the camera MPU 125 calculates the focus lens position (peak position) corresponding to the peak of the contrast focus evaluation value, and drives the focus lens 104 via the focus drive circuit 116 with the peak position as the target position. After the focus lens 104 reaches the target position, the camera MPU 125 determines that the subject can be focused and ends the hybrid AF control.

  In step S319, the camera MPU 125 determines whether or not the contrast AF scanning operation should be completed. Note that the scan completion condition may be, for example, a case where a peak cannot be detected despite scanning from the closest end to the infinite end, but may be based on other determinations. If it is determined that the scan operation should be completed, the process proceeds to S320, and if not, the process proceeds to S323.

  In S320, the camera MPU 125 drives the focus lens 104 via the focus driving circuit 116 with a predetermined fixed point position as a target position. After the focus lens 104 reaches the target position, the camera MPU 125 determines that the subject cannot be focused and ends the hybrid AF control. Although the target position here is a fixed point position determined in advance, it may be an arbitrary position including the current position.

  In S323, the camera MPU 125 calculates the driving amount of the focus lens 104 based on the depth of focus and the degree of focus of the contrast focus evaluation value, and drives the focus lens 104 via the focus driving circuit 116. Here, the camera MPU 125 also performs reversal of the scan direction as necessary. Thereafter, the process returns to S302.

  Next, specific examples and effects of the hybrid AF control according to the first embodiment will be described with reference to FIG. In the description of FIG. 4, it is assumed that the threshold value of the phase difference drive completion counter is 1. Further, it is determined in S202 of FIG. 2 that the reliability of the phase difference focus evaluation value is low, and the focus lens 104 (focus adjustment member) is driven to the closest side by the preceding drive of S204.

  In the example of FIG. 4, when the hybrid AF control is started, the phase difference driving completion counter is 0, the phase difference driving flag is cleared, and the reliability of the phase difference focus evaluation value is low. Therefore, in FIG. 3, the process passes through S305, S306, S312, S315, and S319, reaches S323, and scan driving (contrast AF) is executed. This state is indicated by “(1)” in FIG. As a result of the scan driving, the reliability of the phase difference focus evaluation value becomes high (that is, the phase difference focus evaluation value can be used), but at this time, the defocus amount is not within the depth of focus. Therefore, the process reaches S311 through S306, S307, and S310, and driving based on the defocus amount (imaging surface phase difference AF) is performed. However, for example, due to the drive characteristics of the focus lens 104, the focus lens 104 moves more than necessary and passes through the in-focus position. This state is indicated by “(2)” in FIG. As a result of driving based on the defocus amount (that is, after movement of the focus lens 104 in the imaging surface phase difference AF method), the reliability of the phase difference focus evaluation value becomes low (that is, the phase difference focus evaluation value cannot be used). State). For this reason, the process reaches S313 through S306 and S312, and the phase difference drive completion counter becomes 1. Subsequently, in S331 to S333, determination of the contrast AF scan start position, drive to the scan start position, and setting of the scan direction are performed. This state is indicated by “(3)” in FIG.

  Here, the processing contents and effects of S331 to S333 will be described in detail. After the focus lens 104 is driven by the phase difference focus evaluation value, even if the focus lens 104 passes through the in-focus position (peak position) and the reliability of the phase difference focus evaluation value becomes low, the focus lens 104 reaches the peak. There is a high possibility of being near the position. Therefore, it is possible to preferentially scan the vicinity of the peak position by setting the scan direction to the direction (second direction) opposite to the movement direction (first direction) of the immediately preceding focus lens 104 in S333. Become. Also, if the scan start position is too close to the peak position, the peak position may not be detected properly. Therefore, in step S331, the camera MPU 125 determines a position that is a predetermined distance away from the current position of the focus lens 104 in the moving direction of the focus lens 104 immediately before (before switching the focus adjustment method) as a scan start position. In step S332, the camera MPU 125 moves the focus lens 104 to the scan start position. That is, the camera MPU 125 moves the focus lens 104 from the current position in the same direction as the previous movement direction by a predetermined distance. This improves the speed and accuracy of peak position detection. In order to determine the predetermined distance for determining the scan start position, the camera MPU 125 uses information regarding the reliability of the phase difference (for example, the reliability of the phase difference focus evaluation value), the depth of focus of the optical system, and the like. Can do. The camera MPU 125 can also use information related to the contrast of the subject image (for example, the degree of focus of the contrast focus evaluation value). Further, the camera MPU 125 can use the moving speed of the focus lens 104 in the scanning operation, which is determined from the frame rate or the like. Based on a part or all of these pieces of information, the camera MPU 125 can determine a predetermined distance so that the contrast focus evaluation value necessary for detecting the peak position can be sampled at a minimum, and can determine the scan start position.

  Subsequent to S331 to S333, the process passes through S315 and S319, reaches S323, and scan driving (contrast AF) is executed. This state is indicated by “(4)” in FIG. As a result of the scan drive, the reliability of the phase difference focus evaluation value becomes high (that is, the phase difference focus evaluation value can be used), but this time, since the phase difference drive completion counter has reached the threshold value, the imaging surface Switching to the phase difference AF method is not performed. Therefore, the peak of the contrast focus evaluation value is detected during the scan drive. As a result, the process reaches S316 via S315, and the focus lens 104 is driven to the peak position. This state is indicated by “(5)” in FIG.

  In the example of FIGS. 3 and 4, the camera MPU 125 starts processing for contrast AF, such as scan driving of the focus lens 104 and acquisition of a contrast focus evaluation value, after moving to the scan start position in S332. . However, the present embodiment is not limited to this configuration, and the camera MPU 125 may perform processing for contrast AF even during movement to the scan start position in S332.

  As described above, according to the first embodiment, after the focus lens 104 is driven by the imaging surface phase difference AF method, the digital camera 150 reduces the reliability of the phase difference focus evaluation value. To the imaging surface phase difference AF method. When switching is performed, the digital camera 150 moves the focus lens 104 by a predetermined distance in the moving direction (first direction) before switching, and the scan direction is opposite to the moving direction (first direction) before switching. Set to direction (second direction). Thereby, it is possible to suppress a decrease in focus adjustment speed and accuracy by the hybrid AF method.

[Second Embodiment]
In the first embodiment, the hybrid AF control in the one-shot AF operation at the time of shooting one image has been described. In contrast, in the second embodiment, hybrid AF control in a continuous AF operation or a servo AF operation that automatically repeats the focus adjustment operation so as to maintain the in-focus state of the subject will be described. In the second embodiment, the basic configuration of the digital camera 150 is the same as that of the first embodiment (see FIG. 1). Hereinafter, differences from the first embodiment will be mainly described.

  FIG. 5 is a flowchart for explaining the hybrid AF control in the continuous AF operation executed by the camera MPU 125 according to the second embodiment. Unless otherwise specified, the processing of each step in this flowchart is realized by the camera MPU 125 executing a program stored in the ROM 125a using the RAM 125b as a work memory.

  In S500, the camera MPU 125 starts driving the image sensor 122 in order to perform continuous AF. In S501, the camera MPU 125 waits until the focus evaluation value of the image exposed at the current focus lens position is output (S501). When the focus evaluation value is output, the process proceeds to S502.

  In step S <b> 502, the camera MPU 125 determines whether a continuous AF start instruction has been executed by the switches of the operation switch group 127. If a continuous AF start instruction has been executed, the process proceeds to S503; otherwise, the process of S502 is repeated.

  In step S <b> 503, the camera MPU 125 performs exposure to the image sensor 122. In step S <b> 504, the camera MPU 125 acquires a contrast focus evaluation value from the TVAF focus detection unit 130. In step S <b> 505, the camera MPU 125 acquires a phase difference focus evaluation value from the imaging surface phase difference focus detection unit 129.

  In step S506, the camera MPU 125 determines whether the phase difference focus evaluation value acquired from the imaging surface phase difference focus detection unit 129 in step S505 is high in reliability. When the reliability is high, it is considered that this phase difference focus evaluation value can be used for the phase difference AF method. This reliability includes information on at least one of the matching degree and contrast of a pair of images obtained as a result of the imaging surface phase difference AF. If it is determined that the reliability is high, the process proceeds to S507; otherwise, the process proceeds to S508.

  In step S507, the camera MPU 125 determines whether the defocus amount of the phase difference focus evaluation value is outside the depth of focus. If it is determined that the defocus amount is outside the depth of focus, the process proceeds to S509; otherwise, the process proceeds to S511.

  In step S509, the camera MPU 125 performs hybrid AF control using the imaging surface phase difference AF method and the contrast AF method. Details of the processing here are the same as those described with reference to FIG. 3 in the first embodiment. However, the threshold value in S305 of FIG. 3 may be larger than that in the first embodiment. That is, when operating in continuous AF (first operation mode), the camera MPU 125 may increase the threshold value of the phase difference drive completion counter compared to the case of one-shot AF (second operation mode). . In S300 of FIG. 3, the phase difference drive completion counter is initialized. Therefore, in the continuous AF, the phase difference drive completion counter is initialized for each focus adjustment.

  In step S510, the camera MPU 125 stores the current contrast focus evaluation value in preparation for the next focus adjustment operation. Thereafter, the process proceeds to S511.

  If it is determined in S506 that the reliability of the phase difference focus evaluation value is low, in S508, the camera MPU 125 determines whether or not the contrast focus evaluation value varies with respect to the value stored in S510 described above. Note that the contrast focus evaluation value fluctuation condition is generally determined based on the difference in contrast focus evaluation value, but the amount of fluctuation and the number of fluctuations of the contrast focus evaluation value are arbitrary. The detailed explanation is omitted. If it is determined that the contrast focus evaluation value has fluctuated, the process proceeds to S509, and if not, the process proceeds to S511.

  If it is determined in S507 that the defocus amount is not outside the depth of focus, if it is determined in S508 that the contrast focus evaluation value has not changed, or the process of S510, the process of S511 is executed. In step S <b> 511, the camera MPU 125 determines whether a continuous AF termination instruction has been executed by the switches of the operation switch group 127. When a continuous AF end instruction is executed, the process of this flowchart ends. Otherwise, the process returns to S503, and the same process is repeated.

  As described above, according to the second embodiment, in the continuous AF operation that automatically repeats the focus adjustment operation, it is possible to suppress a decrease in focus adjustment speed and accuracy by the hybrid AF method.

  In the present embodiment, the continuous AF operation has been described as an example of the AF operation that automatically repeats the focus adjustment operation. However, the configuration of the present embodiment can also be applied to servo AF and the like.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  DESCRIPTION OF SYMBOLS 100 ... Lens unit, 104 ... Focus lens, 120 ... Camera body, 122 ... Image sensor, 125 ... Camera MPU, 129 ... Imaging surface phase difference focus detection part, 130 ... TVAF focus detection part, 150 ... Digital camera

Claims (8)

Focus adjusting means for adjusting the focus so as to focus on the subject by moving the focus adjusting member;
Switching means for switching the focus adjustment method used by the focus adjustment means from the phase difference method based on the phase difference of a pair of subject images to the contrast method based on the contrast of the subject images during the focus adjustment;
With
When switching from the phase difference method to the contrast method is performed by the switching unit, the focus adjustment unit moves the focus adjustment member by a predetermined distance in the same first direction as the movement direction before the switching. Then, the focus adjustment is performed by the contrast method by moving from the moved position in a second direction opposite to the first direction. When switching from the phase difference method to the contrast method is performed by the switching unit, the focus adjustment unit moves the focus adjustment member in the first direction by the predetermined distance, and then the contrast method. The focus adjustment apparatus according to claim 1, wherein the focus adjustment is started. The predetermined distance is selected from among the reliability of the phase difference, the depth of focus of the optical system including the focus adjustment member, the contrast of the subject image, and the moving speed of the focus adjustment member in the focus adjustment using the contrast method. The focus adjustment device according to claim 1, wherein the focus adjustment device is based on at least one. The switching means performs switching from the phase difference method to the contrast method when the reliability of the phase difference is less than a threshold value after the focus adjustment member is moved by the phase difference method. Item 4. The focus adjustment apparatus according to any one of Items 1 to 3. The focus adjustment apparatus according to claim 3 or 4, wherein the reliability of the phase difference is based on at least one of a matching degree and a contrast of the pair of subject images. A focus adjustment device according to any one of claims 1 to 5,
Imaging means;
An imaging apparatus comprising: A method for controlling a focus adjustment device, comprising:
A focus adjustment step for adjusting the focus to focus on the subject by moving the focus adjustment member;
A switching step of switching the focus adjustment method used in the focus adjustment step from the phase difference method based on the phase difference of a pair of subject images to the contrast method based on the contrast of the subject images during the focus adjustment;
With
When switching from the phase difference method to the contrast method is performed in the switching step, the focus adjustment step moves the focus adjustment member by a predetermined distance in the same first direction as the movement direction before the switching. The focus adjustment is performed by the contrast method by moving in the second direction opposite to the first direction from the position after the movement.   The program for functioning a computer as each means of the focus adjustment apparatus of any one of Claims 1 thru | or 5.

Images