Focusing control device, imaging apparatus, focusing control method, and focusing control program

Abstract

To provide a focusing control device, an imaging apparatus, a focusing control method, and a focusing control program.SOLUTION: A focusing control device performs focusing control in every frame period of photographing, and comprises a processor. The processor predicts, in the N-th frame period, a lens driving time for moving a focus lens to a first target focus position in the N+1-th frame period, on the basis of first time series AF information including AF information obtained in the N-1-th frame period, and selects a method for driving the focus lens to be executed in the N-th frame period on the basis of the predicted lens driving time.SELECTED DRAWING: Figure 18

Description

[Technical Field]

[0001] The technology of the present disclosure relates to a focus control device, an imaging device, a focus control method, and a focus control program. [Background technology]

[0002] Patent document 1 describes an imaging device in which a focus lens moves in accordance with instructions from a processor to avoid the period of main exposure by the image sensor, and continuous shooting is performed by the image sensor performing main exposure continuously at predetermined time intervals, in which the processor calculates a first focus position of the focus lens for the specific subject based on image data obtained by capturing an image of the specific subject by the image sensor with main exposure in a specific frame during the continuous shooting period in which main exposure is performed, and predicts a second focus position of the focus lens for the specific subject several frames ahead of the specific frame by referring to the first focus position during the continuous shooting period, and moves the focus lens toward the second focus position.

[0003] Patent Document 2 describes an imaging device that includes an image sensor having focus detection pixels, focus detection means that performs focus detection of the imaging optical system based on focus detection signals accumulated by the focus detection pixels, continuous shooting means that causes the image sensor to accumulate image signals for recording multiple times, storage means that stores the image signals for recording, prediction means that predicts the focus position of the subject when acquiring the image signals for recording based on the result of focus detection by the focus detection means and information related to the accumulation time of the focus detection signals used for the focus detection, and focus adjustment means that adjusts the focus of the imaging optical system based on the prediction result by the prediction means, and in which the image sensor accumulates signals for focus detection during a period in which the storage means cannot store image signals for recording, and the focus detection means performs focus detection using the focus detection signals acquired during that period. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-066203 Summary of the Invention [Problem to be solved by the invention]

[0005] One embodiment of the technique of the present disclosure provides a focus control device, an imaging device, a focus control method, and a focus control program that are capable of appropriate focusing in response to changes in the movement of a subject or the movement of an imaging device. [Means for solving the problem]

[0006] In order to achieve the above object, the focus control device disclosed herein is a focus control device that performs focus control in each frame period of shooting, and is equipped with a processor, wherein the processor predicts, in the Nth frame period, a lens drive time for moving the focus lens to a first target focus position in the N+1th frame period based on first time-series AF information including AF information obtained in the N-1th frame period, and selects a focus lens drive method to be executed in the Nth frame period based on the predicted lens drive time.

[0007] When the lens drive time is longer than the threshold, it is preferable that the processor selects as the drive method a first drive method that starts driving the focus lens toward the first target focus position at a timing that allows focus control in the N+1th frame period to be completed in time.

[0008] When the lens drive time is longer than the threshold, it is preferable that the processor selects, as the drive method, a first drive method that starts driving the focus lens toward a first target focus position before acquiring AF information for the Nth frame period.

[0009] When the lens drive time to the first target focus position is equal to or less than a threshold, the processor preferably selects as the drive method a second drive method in which a second target focus position for the (N+1)th frame period is predicted based on second time-series AF information including AF information for the Nth frame period, and drive of the focus lens toward the predicted second target focus position is started.

[0010] When the lens drive time to the first target focus position is equal to or less than a threshold, the processor preferably selects as the drive method a second drive method in which a second target focus position for the (N+1)th frame period is predicted based on second time-series AF information including AF information for the Nth frame period, and drive of the focus lens toward the predicted second target focus position is started.

[0011] The AF information is preferably information acquired using phase difference detection pixels arranged in the imaging region of the imaging element.

[0012] When an AF area for acquiring AF information is set within the imaging area, it is preferable that the processor acquires information related to the readout of an image from an image sensor including the imaging area, determines the readout status of the image corresponding to the AF area based on the information, and starts predicting a second target focus position when it determines that the readout of the image corresponding to the AF area has been completed.

[0013] The AF information used in the first time-series AF information is preferably acquired based on a main image captured once in each frame period.

[0014] The AF information used in the first time-series AF information is preferably acquired based on a live view image captured in each frame period.

[0015] The live view image is preferably the most recent live view image among a plurality of live view images captured in each frame period.

[0016] The focus control is preferably performed during continuous shooting, in which main images are captured continuously over a plurality of frame periods while the release button is pressed.

[0017] As a stop control method for stopping a moving focus lens, it is preferable to provide two stop control methods: a first stop control method in which the focus lens is decelerated to a preset speed and then stopped after passing through a constant speed section in which the focus lens is moved at a constant speed, and a second stop control method in which the focus lens is continuously decelerated and stopped without passing through a constant speed section.

[0018] Furthermore, the continuous shooting mode has two modes: a continuous shooting interval priority mode that keeps the continuous shooting interval constant, and a focus priority mode that prioritizes focusing accuracy over the continuous shooting interval, and it is preferable that the processor selects the first stop control method when the focus priority mode is selected as the continuous shooting mode and the F-number of the optical system including the focus lens is equal to or less than a preset value.

[0019] An imaging device according to the technique of the present disclosure includes any one of the focus control devices described above; An imaging element.

[0020] A focusing control method according to the disclosed technology is a focusing control method that performs focusing control in each frame period during shooting, and in the Nth frame period, predicts a lens drive time for moving a focus lens to a first target focusing position in the N+1th frame period based on first time-series AF information including AF information obtained in the N-1th frame period, and selects a focus lens drive method to be executed in the Nth frame period based on the predicted lens drive time.

[0021] A focusing control program according to the disclosed technology causes a processor to execute focusing control in each frame period of shooting, and causes the processor to execute processing including: predicting, in the Nth frame period, a lens drive time for moving the focus lens to a first target focusing position in the N+1th frame period based on first time-series AF information including AF information obtained in the N-1th frame period; and selecting a focus lens drive method to be executed in the Nth frame period based on the predicted lens drive time. [Effects of the Invention]

[0022] According to the technology of the present disclosure, it is possible to achieve appropriate focusing in response to changes in the movement of the subject or the imaging device. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 illustrates an example of the configuration of an imaging device. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of an imaging pixel. [Figure 3] FIG. 2 is a diagram illustrating an example of a configuration of a phase difference detection pixel. [Figure 4] FIG. 2 is a diagram illustrating an example of a pixel array of an image sensor. [Figure 5] FIG. 2 is a block diagram illustrating an example of a functional configuration of a processor. [Figure 6] FIG. 2 is a diagram showing an example of an AF area. [Figure 7] FIG. 10 is a diagram illustrating an example of correlation calculation processing. [Figure 8] FIG. 10 is a diagram illustrating details of correlation calculation processing. [Figure 9] FIG. 10 is a diagram illustrating an example of a correlation curve. [Figure 10] 10A and 10B are diagrams illustrating the processing of a focus position predicting unit and a driving method selecting unit. [Figure 11] FIG. 10 is a diagram showing an example of time-series AF information of a subject that moves relatively slowly. [Figure 12] FIG. 10 is a diagram illustrating a tentative prediction. [Figure 13]FIG. [Figure 14] FIG. 10 is a diagram showing the relationship between the moving speed of a subject and the lens driving time. [Figure 15] FIG. 10 is a diagram showing an example of time-series AF information of a subject that moves relatively quickly. [Figure 16] 10 is a timing chart showing a second driving method. [Figure 17] 4 is a timing chart showing a first driving method. [Figure 18] 10 is a timing chart showing an example in which the first driving method and the second driving method are switched. [Figure 19] 10 is a flowchart showing an example of the flow of processing executed by focus control during continuous shooting. [Figure 20] FIG. 10 is a diagram illustrating the effect of the first driving method. [Figure 21] FIG. 10 is a diagram illustrating the effect of the second driving method. [Figure 22] FIG. 10 is a conceptual diagram of a first modified example. [Figure 23] FIG. 10 is a diagram showing an outline of processing in a first modified example. [Figure 24] 10 is a timing chart of the process of the first modified example. [Figure 25] 10 is a timing chart of the process of the second modified example. [Figure 26] FIG. 10 is a diagram showing patterns of sources from which time-series AF information used in provisional prediction and actual prediction is acquired. [Figure 27] 4 is a graph showing a first stop control method. [Figure 28] 6 is a graph showing a second stop control method. [Figure 29] FIG. 4 is a diagram showing conditions under which a first stop control method is selected. DETAILED DESCRIPTION OF THE INVENTION

[0024] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0025] First, the terms used in the following description will be explained.

[0026] In the following explanation, "IC" is an abbreviation for "Integrated Circuit." "CPU" is an abbreviation for "Central Processing Unit." "ROM" is an abbreviation for "Read Only Memory." "RAM" is an abbreviation for "Random Access Memory." "CMOS" is an abbreviation for "Complementary Metal Oxide Semiconductor."

[0027] "FPGA" is an abbreviation for "Field Programmable Gate Array." "PLD" is an abbreviation for "Programmable Logic Device." "ASIC" is an abbreviation for "Application Specific Integrated Circuit." "OVF" is an abbreviation for "Optical View Finder." "EVF" is an abbreviation for "Electronic View Finder." "CNN" is an abbreviation for "Convolutional Neural Network." "AF" is an abbreviation for "Auto Focus."

[0028] The technology of the present disclosure will be described using an interchangeable lens digital camera as an example of an embodiment of an imaging device. Note that the technology of the present disclosure is not limited to interchangeable lens digital cameras, and can also be applied to digital cameras with an integrated lens.

[0029] 1 shows an example of the configuration of an imaging device 10. The imaging device 10 is a digital camera with interchangeable lenses. The imaging device 10 is composed of a main body 11 and an imaging lens 12 that is interchangeably attached to the main body 11. The imaging lens 12 is attached to the front side of the main body 11 via a camera-side mount 11A and a lens-side mount 12A.

[0030] The main body 11 is provided with an operation device 13 that includes a dial, a release button, a touch panel, etc. and accepts operations by the user. The operation modes of the imaging device 10 include, for example, a still image capturing mode, a video capturing mode, and an image display mode. Furthermore, the still image capturing mode includes a continuous shooting mode. The operation device 13 is operated by the user when setting the operation mode. The operation device 13 is also operated by the user when starting to capture a still image or a video. The operation device 13 is also operated by the user when specifying an AF area to be focused on from within the imaging area.

[0031] The main body 11 is also provided with a viewfinder 14. Here, the viewfinder 14 is a hybrid viewfinder (registered trademark). A hybrid viewfinder is a viewfinder that selectively uses, for example, an optical viewfinder (hereinafter referred to as "OVF") and an electronic viewfinder (hereinafter referred to as "EVF"). The user can observe an optical image or a live view image of the subject displayed by the viewfinder 14 through a viewfinder eyepiece (not shown).

[0032] A display 15 is provided on the rear side of the main body 11. Images based on image signals obtained by imaging, various menu screens, etc. are displayed on the display 15. The user can also observe a live view image displayed on the display 15 instead of the viewfinder 14.

[0033] The main body 11 and the imaging lens 12 are electrically connected by electrical contacts 11B provided on the camera-side mount 11A coming into contact with electrical contacts 12B provided on the lens-side mount 12A.

[0034] The imaging lens 12 includes an objective lens 30, a focus lens 31, a rear end lens 32, and an aperture 33. The components are arranged along the optical axis A of the imaging lens 12 in the following order from the objective side: objective lens 30, aperture 33, focus lens 31, and rear end lens 32. The objective lens 30, focus lens 31, and rear end lens 32 constitute an imaging optical system. The type, number, and arrangement order of the lenses that make up the imaging optical system are not limited to the example shown in FIG. 1 .

[0035] The imaging lens 12 also has a lens driver 34. The lens driver 34 is configured with, for example, a CPU, RAM, and ROM. The lens driver 34 is electrically connected to a processor 40 in the main body 11 via electrical contacts 12B and 11B.

[0036] The lens driving unit 34 drives the focus lens 31 and the diaphragm 33 based on a control signal transmitted from the processor 40. The lens driving unit 34 controls the driving of the focus lens 31 based on a control signal for focus control transmitted from the processor 40 in order to adjust the focus position FP of the imaging lens 12. The processor 40 performs focus position detection using a phase difference method, for example.

[0037] The diaphragm 33 has an aperture whose diameter is variable around the optical axis A. The lens driver 34 controls the driving of the diaphragm 33 based on an aperture adjustment control signal sent from the processor 40 in order to adjust the amount of light incident on the light receiving surface 20A of the image sensor 20.

[0038] The main body 11 also contains an image sensor 20, a processor 40, and a memory 42. The operations of the image sensor 20, the memory 42, the operation device 13, the viewfinder 14, and the display 15 are controlled by the processor 40.

[0039] The processor 40 is configured by, for example, a CPU. In this case, the processor 40 executes various processes based on a program 43 stored in a memory 42. The processor 40 may be configured by a collection of multiple IC chips. The processor 40 and the memory 42 configure a focusing control device.

[0040] The imaging sensor 20 is, for example, a CMOS image sensor. The imaging sensor 20 is disposed so that its optical axis A is perpendicular to the light-receiving surface 20A and is located at the center of the light-receiving surface 20A. Light that has passed through the imaging lens 12 is incident on the light-receiving surface 20A. A plurality of pixels that generate signals by performing photoelectric conversion are formed on the light-receiving surface 20A. The imaging sensor 20 photoelectrically converts the light incident on each pixel to generate and output an image signal D. The imaging sensor 20 is an example of an "imaging element" according to the technology of the present disclosure.

[0041] Furthermore, as an example, a Bayer color filter array is arranged on the light receiving surface 20A of the image sensor 20, and a color filter of any one of R (red), G (green), and B (blue) is arranged opposite each pixel. Note that some of the pixels arranged on the light receiving surface 20A of the image sensor 20 may be phase difference detection pixels for detecting a phase difference related to focus control.

[0042] FIG. 2 shows an example of the configuration of an imaging pixel N. FIG. 3 shows an example of the configuration of phase difference detection pixels P1 and P2. Each of the phase difference detection pixels P1 and P2 receives one of the light beams split in the X direction around the principal ray. Hereinafter, the direction perpendicular to the X direction will be referred to as the Y direction. Furthermore, the X direction corresponds to the horizontal direction, and the Y direction corresponds to the vertical direction. The phase difference detection pixels P1 and P2 are examples of "phase difference pixels" according to the technology of the present disclosure.

[0043] 2, the imaging pixel N includes a photodiode PD as a photoelectric conversion element, a color filter CF, and a microlens ML. The color filter CF is disposed between the photodiode PD and the microlens ML.

[0044] The color filter CF is a filter that transmits light of any one of the colors R, G, and B. The microlens ML collects the light beam LF incident from the exit pupil EP of the imaging lens 12 onto approximately the center of the photodiode PD via the color filter CF.

[0045] 3, each of the phase difference detection pixels P1 and P2 includes a photodiode PD, a light-shielding layer SF, and a microlens ML. Similar to the imaging pixel N, the microlens ML focuses a light beam LF incident from the exit pupil EP of the imaging lens 12 onto approximately the center of the photodiode PD.

[0046] The light-shielding layer SF is formed of a metal film or the like and is disposed between the photodiode PD and the microlens ML. The light-shielding layer SF blocks a part of the light flux LF that is incident on the photodiode PD via the microlens ML.

[0047] In the phase difference detection pixel P1, the light-shielding layer SF blocks light on the negative side in the X direction with respect to the center of the photodiode PD. That is, in the phase difference detection pixel P1, the light-shielding layer SF allows the light flux LF from the negative-side exit pupil EP1 to be incident on the photodiode PD, and blocks the light flux LF from the positive-side exit pupil EP2 in the X direction.

[0048] In the phase difference detection pixel P2, the light-shielding layer SF blocks light on the positive side in the X direction with respect to the center of the photodiode PD. That is, in the phase difference detection pixel P2, the light-shielding layer SF allows the light flux LF from the exit pupil EP2 on the positive side to be incident on the photodiode PD, and blocks the light flux LF from the exit pupil EP1 on the negative side in the X direction.

[0049] That is, the phase difference detection pixel P1 and the phase difference detection pixel P2 have different light-blocking positions in the X direction. The phase difference detection direction by the phase difference detection pixels P1 and P2 is the X direction (that is, the horizontal direction).

[0050] Fig. 4 shows an example of a pixel arrangement of the image sensor 20. In Fig. 4, "R" represents an imaging pixel N provided with an R color filter CF. "G" represents an imaging pixel N provided with a G color filter CF. "B" represents an imaging pixel N provided with a B color filter CF. Note that the color arrangement of the color filters CF is not limited to the Bayer arrangement, and other color arrangements may be used.

[0051] Rows RL including phase difference detection pixels P1 and P2 are arranged every 10 pixels in the Y direction. In each row RL, a pair of phase difference detection pixels P1 and P2 and one imaging pixel N are repeatedly arranged in the Y direction. The arrangement pattern of the phase difference detection pixels P1 and P2 is not limited to the example shown in FIG. 4. For example, a pattern in which a plurality of phase difference detection pixels are arranged on one microlens ML, as shown in FIG. 5 attached to JP 2018-56703 A, may be used.

[0052] Fig. 5 shows an example of the functional configuration of the processor 40. The processor 40 realizes various functional units by executing processes in accordance with a program 43 stored in a memory 42. As shown in Fig. 5, for example, the processor 40 realizes a main control unit 50, an imaging control unit 51, an image processing unit 52, a display control unit 53, and an AF control unit 55.

[0053] The main control unit 50 performs overall control of the operation of the imaging device 10 based on output information from the operation device 13. The imaging control unit 51 controls the imaging sensor 20 to perform imaging processing that causes the imaging sensor 20 to perform imaging operations. The imaging control unit 51 drives the imaging sensor 20 in a still image imaging mode or a video imaging mode.

[0054] The imaging sensor 20 outputs an image signal D including an imaging signal generated by the imaging pixel N and a phase difference pixel signal generated by the phase difference detection pixels P1 and P2.

[0055] The image processing unit 52 acquires the image signal D output from the imaging sensor 20, and performs image processing such as demosaic processing on the acquired image signal D.

[0056] The display control unit 53 causes the display 15 to display an image represented by the image signal D that has been subjected to image processing by the image processing unit 52. Furthermore, during an imaging preparation operation before capturing a still image or a video, the display control unit 53 causes the display 15 to display a live view image based on the image signal D that is periodically input from the image processing unit 52. Furthermore, the display control unit 53 can also cause the display 15 to display a post-view image that displays the captured actual image after the actual exposure.

[0057] The AF control unit 55 performs focusing control by adjusting the focus lens 31 to the in-focus position FP. The AF control unit 55 is composed of an AF area setting unit 54, a phase difference pixel signal acquisition unit 56, an AF calculation unit 57, an AF information recording unit 61, a focusing position prediction unit 62, a drive method selection unit 63, and a subject detection unit 64.

[0058] The AF area setting unit 54 sets an AF area RA, which is an area to be focused within the imaging area 20B. For example, as shown in Fig. 6, the AF area setting unit 54 sets an area including a subject detected as a focus target by the subject detection unit 64 as the AF area RA.

[0059] The subject detection unit 64 recognizes a subject based on the image signal D using image recognition technology based on a pattern matching method or an AI (Artificial Intelligence) method. Recognized subjects include human faces, animals, automobiles, and airplanes. The subject detection unit 64 can continuously detect a subject, for example, when a user is framing a shot while pressing the release button halfway to check the composition, or when a user is performing continuous shooting by continuously taking multiple images while pressing the release button all the way. This allows the AF area RA to track the subject even if it moves. The subject detection unit 64 continuously outputs information about the AF area RA, which moves in accordance with the movement of the subject, to the AF area setting unit 54.

[0060] In the example shown in FIG. 6, the subject is a person running, and the AF area RA is set to a rectangular area that includes the face of the person detected by the subject detection unit 64.

[0061] The AF area setting unit 54 can also set an area specified by the user via the operation device 13 as the AF area RA. For example, the operation device 13 is a touch panel provided on the display surface of the display 15, and the user can specify the AF area RA by touching the touch panel with a finger.

[0062] The phase difference pixel signal acquisition section 56 acquires a phase difference image signal Dp within the AF area RA from the image signal D output from the imaging sensor 20. The phase difference image signal Dp is the pixel value of the phase difference detection pixels P1 and P2.

[0063] The AF calculation unit 57 calculates the defocus amount DF within the AF area RA by performing correlation calculations based on the phase difference detection pixels P1 and P2 within the AF area RA. The defocus amount DF represents the amount of deviation from the in-focus position FP, and the main control unit 50 adjusts the in-focus position FP by driving the focus lens 31 via the lens drive unit 34 based on the defocus amount DF. As a result, the subject within the AF area RA becomes in-focus.

[0064] 7 shows an example of correlation calculation processing. The AF calculation unit 57 calculates a defocus amount DF by performing correlation calculation using a first image IP1 configured from signals from a plurality of phase difference detection pixels P1 included in a block BL and a second image IP2 configured from signals from a plurality of phase difference detection pixels P2.

[0065] The correlation calculation process will be described in detail with reference to Figure 8. For simplicity of explanation, Figure 8 shows the first image IP1 and the second image IP2 as one-dimensional waveforms in the X direction. A known method can be used to calculate the correlation amount between the first image IP1 and the second image IP2. For example, an integrated value (hereinafter referred to as "integrated difference value") of the absolute values ​​of the differences between each point IP1(X,Y) constituting the first image IP1 and each point IP2(X+φ,Y) constituting the second image IP2 is calculated.

[0066] 9 shows an example of a correlation curve representing the relationship between the phase difference φ and the correlation amount between the first image IP1 and the second image IP2. Specifically, FIG. 9 shows a correlation curve representing the relationship between the difference integrated value and the phase difference φ. The AF calculation unit 57 calculates the phase difference φ at which the difference integrated value is minimum (i.e., the correlation amount is maximum) as the defocus amount DF.

[0067] In the case of normal still image shooting, where one main image is captured by a single full press of the release button, focus control is performed using this defocus amount DF as AF information. On the other hand, in the case of continuous shooting, where multiple main images are captured continuously while the release button is fully pressed, the focus position FP is predicted, and focus control is performed using the predicted value of the focus position FP as AF information. This is because if the subject moves during continuous shooting, it will be impossible to make the focus position FP follow the subject's movement unless focus control is performed that predicts the subject's movement.

[0068] The AF control unit 55 uses the time-series AF information TS to predict the in-focus position FP. The AF information recording unit 61 records the time-series AF information TS based on the defocus amount DF output by the AF calculation unit 57. The time-series AF information TS is history information that indicates changes in the AF information over time. The AF information includes the defocus amount DF as well as the in-focus position FP of the focus lens 31 calculated from the defocus amount DF (see FIG. 10). Each time the AF calculation unit 57 outputs the defocus amount DF, the AF information recording unit 61 calculates the in-focus position FP according to the defocus amount DF and records the calculated in-focus position FP in the memory 42. The time-series AF information TS is information that chronologically summarizes the in-focus positions FP (see FIG. 10). Each time the AF calculation unit 57 outputs the defocus amount DF, the AF information recording unit 61 adds the in-focus position FP to the time-series AF information TS as AF information. This updates the time-series AF information TS.

[0069] The AF calculation unit 57 calculates at least one defocus amount DF during a frame period of shooting and outputs it as AF information. In normal shooting, the frame period of shooting is the period during which an actual image is captured by operating the release button. On the other hand, in continuous shooting, as an example, one frame period is the period from the preparatory operation for the actual exposure to capture the actual image to the preparatory operation for the next actual exposure. In normal shooting, one actual image is captured by one full press of the release button, so one frame period is the period from one full press of the release button to the end of capturing the actual image. On the other hand, in continuous shooting, one frame period is determined according to the interval between continuous shootings that corresponds to a preset frame rate. The frame rate is, for example, several frames per second to several tens of frames per second. In continuous shooting, the AF calculation unit 57 outputs one piece of AF information per frame period, and the AF information recording unit 61 updates the time-series AF information TS for each frame period.

[0070] As shown in FIG. 10, the focus position prediction unit 62 predicts a focus position FP according to the movement of the subject based on the time-series AF information TS. The focus position prediction unit 62 performs preliminary prediction and final prediction using different time-series AF information TS. The time-series AF information TS includes the focus position FP in the current frame period as the latest AF information and multiple focus positions FP in multiple past frame periods as multiple past AF information. As shown in FIG. 10, if the current frame is the Nth frame period, the focus position FP(N) in the Nth frame period is the latest AF information. The focus position FP(N-1) in the N-1th frame period is the AF information one frame earlier, and the focus position FP(N-2) in the N-2th frame period and the focus position FP(N-3) in the N-3th frame period are the AF information for the frame two frames earlier and the AF information for the frame three frames earlier, respectively.

[0071] The time-series AF information TS(N) is information that includes the in-focus position (N) of the Nth frame period, which is the current frame period, as the latest AF information, and is an example of "second time-series AF information" according to the technology of the present disclosure. On the other hand, the time-series AF information TS(N-1) is information that includes the in-focus position (N-1) of the N-1th frame period as the latest AF information, and is an example of "first time-series AF information" according to the technology of the present disclosure.

[0072] The focus position predicting unit 62 predicts, as a provisional prediction, a target focus position FPT1(N+1) for the N+1-th frame period based on time-series AF information (N-1) including, as AF information, the focus position FP(N-1) obtained in the N-1-th frame period. Then, as a final prediction, the focus position predicting unit 62 predicts, as a final prediction, a target focus position FPT2(N+1) for the N+1-th frame period based on time-series AF information (N-1) including, as AF information, the focus position FP(N) obtained in the N-th frame period. The provisional prediction and the final prediction use different time-series AF information TS on which the prediction is based, but the same target is predicted. That is, the target is a future target focus position FPT(N+1) for the frame period immediately following the N-th frame period. In this way, the prediction target is the same in both tentative prediction and actual prediction, but because the time-series AF information TS on which the prediction is based is different, the target focus position FPT(N+1) is distinguished as target focus position FPT1(N+1) in the case of tentative prediction and target focus position FPT2(N+1) in the case of actual prediction. The target focus position FPT1(N+1) of the tentative prediction is an example of a "first target focus position" according to the technology of the present disclosure, and the target focus position FPT2(N+1) of the actual prediction is an example of a "second target focus position" according to the technology of the present disclosure.

[0073] Based on the target focus position FPT1(N+1) predicted in the tentative prediction, the drive method selection unit 63 predicts the lens drive time LDT for moving the focus lens 31 to the target focus position FPT1(N+1). Then, based on the predicted lens drive time LDT, the drive method selection unit 63 selects the drive method for the focus lens 31 to be executed in the Nth frame period. The drive method for the focus lens 31 to be executed in the Nth frame period is a drive method to be executed in the Nth frame period in order to move the focus lens 31 to the focus position FP at the timing of the main exposure in the N+1th frame period.

[0074] The drive method selection unit 63 selects the first drive method as the drive method when the predicted lens drive time LDT is longer than a preset threshold value TH, and selects the second drive method when the predicted lens drive time LDT is equal to or shorter than the preset threshold value TH.

[0075] The first driving method is a method in which the focus lens 31 is started to be driven toward the target focus position FPT1(N+1), which is the tentatively predicted value, without performing a main prediction. Because the first driving method does not perform a main prediction, it is a driving method that can ensure a long lens drive time LDT and is suitable for a fast-moving subject. The first driving method can be said to be a time-priority driving method. From the viewpoint of purpose, the first driving method is a driving method in which the focus lens 31 is started to be driven toward the target focus position FPT1 within the Nth frame period at a timing that allows focus control in the N+1th frame period to be completed in time. Furthermore, from the viewpoint of the timing to start driving the focus lens 31, the first driving method is a driving method in which the focus lens 31 is started to be driven toward the first target focus position before AF information (e.g., defocus amount DF or focus position FP(N+1)) for the Nth frame period is acquired.

[0076] On the other hand, the second driving method is a driving method that performs a tentative prediction followed by a final prediction. Specifically, the target focus position FPT2(N+1) for the (N+1)th frame period is predicted based on time-series AF information TS(N) that includes the focus position FP(N) for the Nth frame period as AF information. The second driving method then starts driving the focus lens 31 toward the predicted target focus position FPT2(N+1). In other words, since the second driving method performs the final prediction, the lens drive time is shorter than that of the first driving method, but it is a driving method that prioritizes accuracy and enables highly accurate focusing. The second driving method is a driving method suitable for slow-moving subjects.

[0077] When the driving method selection unit 63 selects the first driving method, it outputs a defocus amount DF1 according to the target focusing position FPT1(N+1) and a driving start timing signal STM1. On the other hand, when the second driving method is selected, it outputs a defocus amount DF2 according to the target focusing position FPT2(N+1) and a driving start timing signal STM2. The driving start timing signals STM1 and STM2 are examples of the driving start timing signal STM shown in FIG.

[0078] In the imaging device 10, the configuration including the processor 40 that functions as the AF control unit 55 is an example of a "focus control device" according to the technique of the present disclosure.

[0079] The prediction of the in-focus position FP using the time-series AF information TS performed by the AF control unit 55, and the first and second driving methods will be described in more detail with reference to FIGS.

[0080] The subject S1 shown in FIG. 11 is a runner, and is an example of a subject that moves gradually toward the user being photographed by the imaging device 10. The subject distance of the moving subject S1 changes from moment to moment, and the focus position FP also changes in response to this change. As an example, as shown in FIG. 11, the graph shows that the focus position FP gradually increases from time T(N-3) toward T(N), which is the time of the current frame period. The time-series AF information TS is history information that indicates such changes in the focus position FP over time.

[0081] 12 and 13 show the difference between the tentative prediction and the actual prediction using graphs similar to those in FIG. 11. In the tentative prediction shown in FIG. 12, time-series AF information TS(N-1) is used, which includes the focus position FP(N-1) of the previous frame period one frame before as the latest AF information at time T(N) in the current frame period. In the tentative prediction, the future target focus position FP1(N+1) two frames ahead is predicted based on this time-series AF information TS(N-1). However, because the tentative prediction predicts the focus position FP(N+1) two frames ahead, the prediction accuracy is lower than that of the actual prediction shown in FIG. 13.

[0082] 13, time-series AF information TS(N) including the focus position FP(N) of the current frame period as the latest AF information is used at time T(N) of the current frame period. This prediction predicts the target focus position FP2(N+1) of one frame ahead based on this time-series AF information TS(N). This prediction predicts the focus position FP(N+1) of one frame ahead, and therefore has higher prediction accuracy than tentative prediction.

[0083] When the subject distance changes from moment to moment, as in the case of subject S1 shown in Fig. 11, the faster the subject's moving speed during continuous shooting (i.e., the rate at which the subject distance changes), the longer the lens drive time LDT, as shown in Fig. 14. This is because, in order to perform accurate focusing control, the faster the subject's moving speed, the greater the amount of change in focus position FP per unit time, and the amount of drive of focus lens 31 that must be moved per unit time also increases in accordance with the amount of change in focus position FP per unit time.

[0084] Subject S2 shown in Fig. 15 is a car, and like subject S1 in Fig. 11, is an example of a subject whose subject distance changes in a direction approaching image capture device 10. Because subject S2 moves faster than subject S1, the amount of change per unit time in focus position FP also increases, and the slope of the graph in Fig. 15 is steeper than that of the graph in Fig. 11. The greater amount of change per unit time in focus position FP means that when continuously capturing images of subject S2, the amount of drive of focus lens 31 that must be moved per unit time in each frame period also increases compared to when continuously capturing images of subject S1.

[0085] When the moving speed is fast, as in the case of subject S2 shown in Fig. 15, the first driving method, which prioritizes time, is preferable although the focusing accuracy is reduced, and when the moving speed is slow, as in the case of subject S1 shown in Fig. 11, there is more time and the second driving method, which has high focusing accuracy, is preferable. Therefore, the AF control unit 55 predicts the lens driving time LDT according to the target focusing position FPT1(N+1) predicted by the tentative prediction, and selects the driving method for the focus lens 31 based on the predicted lens driving time LDT.

[0086] 16 to 18 are timing charts showing the operation of each part of imaging device 10 when focusing control is performed during continuous shooting. FIG. 16 is a timing chart when the first drive method is selected as the method for driving focus lens 31, and FIG. 17 is a timing chart when the second drive method is selected. FIG. 18 is a timing chart when the first drive method and the second drive method are switched during continuous shooting. Also, FIGS. 16 to 18 show an example of post-view continuous shooting in which images captured during continuous shooting are displayed on viewfinder 14 or display 15 after capture. An image displayed in post-view continuous shooting will be referred to as a post-view image below. In addition to post-view continuous shooting, the continuous shooting mode also includes live-view continuous shooting in which a live-view image is displayed after main exposure, as will be described later (see FIG. 25).

[0087] First, as shown in FIG. 16 as a representative example, each frame period is the period from the preparatory operation of the shutter through the actual exposure, when the shutter closes, until the preparatory operation of the shutter for the next frame begins. The shutter is, for example, a mechanical shutter having a front curtain and a rear curtain, and the shutter has four states: a front curtain closed state, a rear curtain closed state, a fully open state, and a fully closed state. The front curtain closed state is a state in which the front curtain is in a closed position and the rear curtain is in an open position, and the rear curtain closed state is a state in which the rear curtain is in a closed position and the front curtain is in an open position. The fully open state is a state in which both the front curtain and the rear curtain are in an open position. The fully closed state is a state in which both the front curtain and the rear curtain are in a closed position. In the case of postview continuous shooting, the shutter is in a fully closed state while a postview image is displayed, so the shutter transitions among three states: a front curtain closed state, a rear curtain closed state, and a fully closed state.

[0088] The period indicated by "open" in FIG. 16 is the period of actual exposure, during which the front curtain transitions from a closed state to a closed state. Specifically, the period indicates the period during which the front curtain moves from a closed position to an open position, and the rear curtain moves from an open position to a closed position after the front curtain, thereby causing the slit-shaped exposure opening to move across the entire imaging area 20B. During this period, subject light is incident across the entire imaging area 20B. The exposure time during this period is set as the shutter speed. The period indicated by diagonal hatching before "open" is the period of preparatory operation of the shutter before the actual exposure. During this preparatory operation, the front curtain is wound up from the open position to the closed position, and the rear curtain is moved from the closed position to the open position. When the actual exposure is completed, the rear curtain is also wound up to the closed position and becomes fully closed. During this period, the actual exposed image is read out from the imaging sensor 20 (indicated as "readout" in FIG. 16 and other figures). After the actual image is read out, a postview image is displayed in the viewfinder 14 and other figures. The post-view image is updated each time the main image is read out in each frame period.

[0089] After the main image is read, the AF calculation unit 57 performs phase difference AF calculation to obtain AF information. Then, the time-series AF information TS is updated with the AF information obtained by the AF information recording unit 61. The next frame period starts again with the shutter preparation operation.

[0090] Assuming that the current frame period is the Nth frame period, for example, the preliminary prediction is performed after the start of the Nth frame period and before the readout of the main exposure is completed. In the example of FIG. 16, the preliminary prediction is performed during the main exposure. In this preliminary prediction, the target focus position FPT1(N+1) for the N+1th frame period is predicted based on the time-series AF information TS(N-1). The two-dot chain arrow extending from the preliminary prediction to the main exposure of the next frame period indicates that the target focus position FPT1 for the main exposure of the next frame period is the target focus position FPT1. Furthermore, the solid arrows extending from the time-series AF information TS to the preliminary prediction and the main prediction indicate the time-series AF information TS that is the basis for the preliminary prediction and the main prediction, respectively. In other words, the time-series AF information TS used as the basis for the preliminary prediction is the time-series AF information TS with the AF information for the previous frame period as the latest, and the time-series AF information TS used as the basis for the main prediction is the time-series AF information TS with the AF information for the current frame period as the latest.

[0091] Then, a driving method is selected based on the target focusing position FPT1(N+1) predicted in the preliminary prediction. In the example of Fig. 16, since the second driving method is selected, the main prediction is performed after the preliminary prediction. In the second driving method, after the main prediction, driving of the focus lens 31 toward the target focusing position FPT2(N+1) predicted in the main prediction is started.

[0092] The timing chart shown in Fig. 17 is an example in which the first driving method is selected, and the process up to the update of the time-series AF information TS and the provisional prediction is the same as that in Fig. 16. When the first driving method is selected, the actual prediction is not performed, and driving of the focus lens 31 toward the target focusing position FPT1(N+1) predicted in the provisional prediction is started.

[0093] The timing chart shown in Figure 18 is basically the same as Figures 16 and 17, but in this example, the first driving method is selected during the N-1th frame period during continuous shooting, but the second driving method is selected during the Nth frame period and the N+1th frame period.

[0094] The operation of the technique of the present disclosure will be described using the timing chart shown in FIG. 18, the flowchart of focus control during continuous shooting shown in FIG. 19, and the diagrams showing the effects shown in FIGS.

[0095] Assuming that the continuous shooting mode is set, when a command to start continuous shooting is input by fully pressing the release button in step S110 shown in Fig. 19, the AF control unit 55 starts focus control during continuous shooting. When continuous shooting starts, the AF control unit 55 repeatedly executes processes such as post-view, shutter operation, main exposure, readout, AF calculation, and update of the time-series AF information TS shown in Fig. 18 based on the frame rate of the continuous shooting mode.

[0096] In step S120, one frame period (N) starts (Y in step S120), and when the shutter starts to open, the main exposure starts, as shown in Fig. 18. At this timing, the AF control unit 55 tentatively predicts the target focusing position FPT1(N+1) based on the time-series AF information TS(N-1) of the immediately previous frame period (N-1) read from the memory 42 (step S130).

[0097] In step S140, the AF control unit 55 calculates the lens drive time LDT for moving the focus lens 31 from the current position to the target focus position FPT1(N+1) based on the tentatively predicted target focus position FPT1(N+1). In this way, the lens drive time LDT is predicted.

[0098] In step S150, the AF control unit 55 compares the calculated lens drive time LDT with the threshold value TH, and if the lens drive time LDT is longer than the threshold value TH (Y in step S150), the AF control unit 55 proceeds to step S160, where it selects the first drive method that prioritizes time.Then, it proceeds to step S170, where it starts driving the focus lens 31 toward the target in-focus position FPT1(N+1).

[0099] When the subject moves quickly, as in the case of subject S2 shown in Fig. 20, the amount of change in focus position FP per unit time is large, and therefore the lens drive time LDT required for focus control is long. When the frame rate of continuous shooting is constant, the focus lens 31 needs to be moved by the next frame period. According to the first drive method, since the focus lens 31 starts to be driven toward the provisionally predicted target focus position FPT1(N+1) without performing actual prediction, a relatively long lens drive time LDT can be ensured by the next frame period.

[0100] On the other hand, if the lens drive time LDT is equal to or less than the threshold value TH (N in step S150), the AF control unit 55 proceeds to step S180 and selects the second drive method that prioritizes accuracy. 18, the AF calculation is performed after the main exposure and the readout of the main image, and the AF control unit 55 acquires the latest AF information for the current Nth frame period through the AF calculation. Then, the AF control unit 55 performs a main prediction based on the time-series AF information TS(N) including the acquired latest AF information. Then, the AF control unit 55 performs a main prediction of the target focus position FPT2(N+1) based on the time-series AF information TS(N). Then, the process proceeds to step S210, where the focus lens 31 starts to be driven toward the target focus position FPT2(N+1).

[0101] In the case of a subject that moves slowly, such as subject S1 shown in FIG. 21, the amount of change in the focus position FP per unit time is small, so the lens drive time LDT required for focus control is short. According to the second drive method, the target focus position FPT2(N+1) for the next frame is predicted based on the time-series AF information TS(N) including AF information for the current Nth frame period. This ensures better focusing accuracy than the first drive method. Furthermore, because the lens drive time LDT is relatively short, the focus lens 31 can be moved to the target focus position FPT2(N+1) by the time of the next frame period. The AF control unit 55 repeats the above process until continuous shooting is completed (step S220).

[0102] As described above, with the focus control device including the AF control unit 55 according to the technology of the present disclosure and the image capture device 10 including the focus control device, in the Nth frame period, the lens drive time LDT for moving the focus lens 31 to the first target focus position (for example, target focus position FPT1(N+1)) for the N+1th frame period is predicted based on the first time-series AF information (for example, time-series AF information TS(N-1)) including AF information obtained in the N-1th frame period (for example, focus position (N)). Then, based on the predicted lens drive time LDT, a drive method for the focus lens 31 to be executed in the Nth frame period is selected. This enables appropriate focusing in response to changes in the movement of the subject. Furthermore, even if the image capture device 10 moves relative to the subject instead of or in addition to the movement of the subject, appropriate focusing in response to changes in the movement of the image capture device 10 is also possible.

[0103] Furthermore, when the lens drive time LDT is longer than the threshold value TH, the processor 40 functioning as the AF control unit 55 selects the first drive method, which starts driving the focus lens 31 toward the target focus position FPT1(N+1) at a timing that allows focus control in the N+1th frame period to be completed in time. This improves focus tracking ability for fast-moving subjects even in the case of continuous shooting, where ensuring the lens drive time LDT is difficult depending on the frame rate.

[0104] When the lens drive time LDT is longer than the threshold value TH, the processor 40 functioning as the AF control unit 55 selects the first drive method, which starts driving the focus lens toward the target focus position FPT1(N+1) before acquiring the focus position (N) for the Nth frame period. This improves the ability to track the focus on a fast-moving subject such as the subject S2 shown in FIG.

[0105] Furthermore, when the lens drive time LDT to the target focus position FPT1(N+1) is equal to or less than the threshold value TH, the processor 40 functioning as the AF control unit 55 selects, as the drive method, a second target focus position (for example, target focus position FPT2(N+1)) for the N+1th frame period based on second time-series AF information (for example, time-series AF information TS(N)) including the focus position FP(N) for the Nth frame period, and selects a second drive method in which the focus lens 31 starts to be driven toward the predicted target focus position FPT2(N+1). Therefore, when the movement of the subject is slow, such as the subject S1 shown in FIG. 21, good focusing accuracy can be ensured.

[0106] In the above embodiment, the AF information, which indicates the in-focus position FP as an example, is information acquired using the phase difference detection pixels P1 and P2 arranged in the imaging region 20B of the image sensor 20. By distributing the phase difference detection pixels P1 and P2 within the imaging region 20B, the range of the AF area RA that can be set is expanded within the imaging region 20B, thereby improving focus tracking performance for moving subjects. Furthermore, the phase difference detection method generally has the advantage of faster focusing speed than the contrast method. However, in the technology disclosed herein, the contrast method may be used as the focusing method instead of the phase difference detection method.

[0107] In the above embodiment, the AF information used in the first time-series AF information that forms the basis of the provisional prediction is obtained based on a main image captured once in each frame period. The main image has a higher resolution than, for example, a live view image, and therefore, the prediction accuracy of the lens drive time LDT may be improved.

[0108] In the above embodiment, focus control is performed during continuous shooting, in which actual images are captured continuously over multiple frame periods while the release button is pressed. During continuous shooting, the frame period is limited by the frame rate, making it difficult to ensure the lens drive time LDT. In such cases, the technology disclosed herein is particularly effective.

[0109] Various modifications of the above embodiment will be described below.

[0110] [First Modification] In the above embodiment, when performing the main prediction to predict the target focus position FPT2(N+1), an example was described in which the AF calculation is performed after completing the reading of all pixels of the main image, but the AF calculation may also be started before reading of all pixels, as in the first modified example shown in Figures 22 to 24.

[0111] As shown in FIG. 22, when an AF area RA for acquiring AF information is set within the imaging area 20B, the processor 40 acquires information regarding the readout of the image of the imaging sensor 20 including the imaging area 20B, determines the readout status of the image corresponding to the AF area RA based on the acquired information, and when it determines that the readout of the image corresponding to the AF area RA has been completed, may start predicting a target focusing position FPT2(N+1), which is an example of a second target focusing position.

[0112] In this case, as shown in FIG. 23 , the main control unit 50 acquires information related to image readout from the imaging control unit 51. The image readout of the imaging region 20B is line readout, and the information related to image readout is, for example, information indicating up to which line the imaging sensor 20 has completed readout. The main control unit 50 acquires the information related to image readout from the imaging control unit 51 and determines the timing to start AF calculation. The main control unit 50 determines the readout status of the image corresponding to the AF area RA based on the acquired information, and when it determines that the readout of the image corresponding to the AF area RA has been completed, it commands the AF calculation unit 57 to start AF calculation without waiting for the completion of readout of all pixels. The time-series AF information TS is updated by the AF information calculated by the AF calculation unit 57. The focus position prediction unit 62 starts main prediction of the target focus position FPT2(N+1) based on the updated time-series AF information TS(N).

[0113] 16, in which the AF calculation starts after the readout of all pixels is completed, the AF calculation can be started earlier by ΔT as shown in FIG. 24, and the start timing of the main prediction performed after the AF calculation can also be earlier by up to ΔT. As a result, the lens drive time LDT can also be secured to be longer by up to ΔT. ΔT is the readout time of the remaining images after the AF area RA shown in FIG. 22.

[0114] [Second Modification] In the above embodiment, the AF information used in the first time-series AF information (for example, time-series AF information (N-1)) that forms the basis of the provisional prediction is obtained based on an actual image captured once in each frame period. However, as shown in Fig. 25, when live view continuous shooting is performed, the AF information may be obtained from a live view image instead of an actual image.

[0115] First, in live view continuous shooting, after the readout of the main image is completed, the shutter is fully open. In this state, a live view image is captured using the electronic shutter function of the image sensor 20. The captured live view image is displayed on the viewfinder 14 or display 15. In the example shown in Figure 25, a live view image is captured three times in each frame period. While the shutter is operating to capture the main image, it is no longer possible to capture a live view image, so the viewfinder 14 or display 15 is blacked out and no live view image is displayed.

[0116] In each frame period, the live view image is captured after the main image. Therefore, since the live view image is captured later in time than the main image, it reflects the most recent position of the subject compared to the main image. Since the provisional prediction is based on time-series AF information including this latest AF information, the prediction accuracy of the focus position FP may be improved.

[0117] Furthermore, it is preferable that the AF information be obtained from the most recent live view image among multiple live view images captured in each frame period, since the most recent live view image among multiple live view images reflects the most recent position of the subject.

[0118] The sources of acquisition of the first time-series AF information used for provisional prediction and the second time-series AF information used for final prediction can be organized as shown in Figure 26. In Figure 26, the first pattern is a pattern in which the acquisition source for both is the final image, as shown in Figures 16 to 18. The second pattern is the example shown in Figure 25, in which the acquisition source for the first time-series AF information used for provisional prediction is a live view image, and the acquisition source for the second time-series AF information used for final prediction is the final image. In addition to these, in the case of live view continuous shooting, the acquisition source for both the first time-series AF information and the second time-series AF information may be the live view image, as shown as a third pattern in Figure 26.

[0119] Furthermore, as described in the above embodiment, the technology of the present disclosure can be applied even when not continuous shooting is in progress. For example, the technology of the present disclosure may be applied when confirming the composition while displaying a live view image by half-pressing the release button, or when simply displaying a live view image without operating the release button. This not only improves the focus tracking performance of the live view image for fast-moving subjects, but also improves the focus accuracy of the live view image for slow-moving subjects. In this way, the technology of the present disclosure can be applied even when capturing an actual image is not involved. When capturing an actual image is not involved, the frame period is the interval at which at least one AF information item is acquired and the time-series AF information is updated using the acquired AF information.

[0120] [Third Modification] 27 to 29 relate to a method of controlling the stopping of focus lens 31. In Figures 27 and 28, the horizontal axis represents time and the vertical axis represents lens movement speed, and the graph shows the change over time in movement speed from the movement start timing (Start) when focus lens 31 starts moving to the stop timing (Stop) when focus lens 31 stops.

[0121] Imaging device 10 has two stop control methods for stopping focus lens 31 while it is moving: a first stop control method, as shown in Fig. 27, in which focus lens 31 is decelerated to a preset speed VL and then stopped after passing through a constant-velocity section CVS in which focus lens 31 moves at a constant velocity; and a second stop control method, as shown in Fig. 28, in which focus lens 31 is continuously decelerated and stopped without passing through a constant-velocity section. The second stop control method shown in Fig. 28 is also called trapezoidal driving because the graph forms a trapezoid. Main controller 50 selects one of the two stop control methods according to preset conditions and stops focus lens 31 using the selected stop control method.

[0122] Here, stopping the focus lens 31 refers to bringing the focus lens 31 to the target focusing position FPT in accordance with the exposure timing, and includes not only the case where the focus lens 31 is completely stopped at the target focusing position FPT but also the case where the focus lens 31 is moving within a predetermined tolerance range based on the target focusing position FPT. The stopped time corresponds to the exposure period according to the shutter speed. The constant speed section also includes the case where the focus lens 31 is moving at a completely constant speed but also the case where the focus lens 31 is moving within a predetermined tolerance range.

[0123] The first stop control method shown in FIG. 27 is used when it is desired to improve the accuracy of the stop position of the focus lens 31. For example, when a bright lens with a small F-number is used as the focus lens 31, the depth of field is shallow, which narrows the focus lens 31's focusing range, resulting in a smaller allowable error range for the stop position. In such cases, high accuracy is required for the stop position. Furthermore, a bright focus lens 31 has a relatively large diameter, which tends to make the focus lens 31 relatively heavy. As a result, the inertial force during movement is large, which often results in overrunning from the target stop position. In the first stop control method shown in FIG. 27, a constant-speed section at a relatively low speed VL is inserted before stopping, thereby suppressing overrunning of the stop position. This improves the accuracy of the stop position compared to the second stop control method shown in FIG. 28.

[0124] FIG. 29 shows conditions under which the first stop control method, which provides high stop position accuracy, is selected. First, as a premise, imaging device 10 has two continuous shooting modes: a continuous shooting interval priority mode, which maintains a constant continuous shooting interval, and a focus priority mode, which prioritizes focusing accuracy over the continuous shooting interval. Processor 40, functioning as main controller 50, selects the first stop control method when focus priority mode is selected as the continuous shooting mode and the F-number of the optical system including focus lens 31 is equal to or less than a preset value. Otherwise, the second stop control method is selected. The preset value is, for example, a relatively bright lens with an F-number of "1.0" or "1.4." Thus, imaging device 10 typically uses the second stop control method to stop focus lens 31 in a short time, while selecting the first stop control method when high stop position accuracy is required, thereby enabling accurate stopping at the target position.

[0125] [Other variations] In the above embodiment, the display control unit 53 displays an image on the display 15, but the display control unit 53 may display an image on the viewfinder 14 instead of or in addition to the display 15. In this case, the focus control device may be configured to allow the user to specify the AF area RA via the eye-gaze input device.

[0126] The technology of the present disclosure is not limited to digital cameras, but can also be applied to electronic devices such as smartphones and tablet terminals that have an imaging function.

[0127] In the above embodiment, the hardware structure of the control unit, with processor 40 being an example, can use the following various processors. The above various processors include a CPU, which is a general-purpose processor that functions by executing software (programs), as well as a processor such as an FPGA, whose circuit configuration can be changed after manufacture. FPGAs include dedicated electrical circuits, such as PLDs or ASICs, which are processors with a circuit configuration designed specifically to execute specific processes.

[0128] The control unit may be configured with one of these various processors, or may be configured with a combination of two or more processors of the same or different types (for example, a combination of multiple FPGAs, or a combination of a CPU and an FPGA). Also, multiple control units may be configured with a single processor.

[0129] There are several possible examples of configuring multiple control units with a single processor. A first example is a form in which one processor is configured with a combination of one or more CPUs and software, as typified by computers such as client and server, and this processor functions as multiple control units. A second example is a form in which a processor is used to realize the functions of an entire system including multiple control units on a single IC chip, as typified by system-on-chip (SOC). In this way, the control unit can be configured as a hardware structure using one or more of the various processors described above.

[0130] Furthermore, more specifically, the hardware structure of these various processors can be an electric circuit that combines circuit elements such as semiconductor elements.

[0131] The program may also be stored in a non-transitory computer-readable storage medium.

[0132] The above-described description and illustrations are a detailed explanation of the parts related to the technology of the present disclosure and are merely an example of the technology of the present disclosure. For example, the above description of the configuration, functions, actions, and effects is an explanation of an example of the configuration, functions, actions, and effects of the parts related to the technology of the present disclosure. Therefore, it goes without saying that unnecessary parts may be deleted, new elements may be added, or replacements may be made to the above-described description and illustrations within the scope of the gist of the technology of the present disclosure. Furthermore, to avoid confusion and facilitate understanding of the parts related to the technology of the present disclosure, the above-described description and illustrations omit explanations of common technical knowledge that do not require particular explanation to enable the implementation of the technology of the present disclosure.

[0133] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0134] The above explanation allows one to understand the following techniques. [Additional note 1] A focusing control device that performs focusing control during each frame period of photography, It has a processor, The processor In the N-th frame period, a lens drive time for moving the focus lens to a first target focus position in the N+1-th frame period is predicted based on first time-series AF information including AF information obtained in the N-1-th frame period; selecting a focus lens driving method to be executed in the Nth frame period based on the predicted lens driving time; Focus control device. [Additional note 2] The processor If the lens drive time is longer than the threshold value, a first drive method is selected as the drive method, in which drive of the focus lens is started toward a first target focus position at a timing in which focus control in the (N+1)th frame period is completed in time. Item 1. A focusing control device according to claim 1. [Additional note 3] The processor If the lens drive time is longer than the threshold value, a first drive method is selected as the drive method, in which drive of the focus lens is started toward a first target focus position before AF information for the Nth frame period is acquired. The focusing control device according to claim 1 or 2. [Additional note 4] The processor When the lens drive time to the first target focus position is equal to or less than the threshold, a second drive method is selected as the drive method, in which a second target focus position for the (N+1)th frame period is predicted based on second time-series AF information including AF information for the Nth frame period, and drive of the focus lens toward the predicted second target focus position is started. A focusing control device according to any one of supplementary items 1 to 3. [Additional note 5] The AF information is information acquired using phase difference detection pixels arranged in the imaging area of ​​the image sensor. A focusing control device according to any one of supplementary items 1 to 4. [Additional note 6] When an AF area for acquiring AF information is set within the imaging area, The processor Obtaining information regarding reading of an image from an imaging element including an imaging area; Based on this information, the camera determines the readout status of the image corresponding to the AF area, When it is determined that the readout of the image corresponding to the AF area is completed, the prediction of the second target focus position is started. 6. A focusing control device according to claim 4 or claim 5. [Additional note 7] The AF information used in the first time-series AF information is acquired based on a main image captured once in each frame period. A focusing control device according to any one of supplementary items 1 to 6. [Additional note 8] The AF information used in the first time-series AF information is acquired based on a live view image captured in each frame period. A focusing control device according to any one of supplementary items 1 to 7. [Additional note 9] The live view image is the latest live view image among a plurality of live view images captured in each frame period. Item 9. A focusing control device according to item 8. [Additional Note 10] The focus control is performed during continuous shooting, in which the main images are captured continuously over a period of multiple frames while the release button is pressed. A focusing control device according to any one of supplementary items 1 to 9. [Additional Note 11] The stop control method for stopping the moving focus lens includes two stop control methods: a first stop control method in which the focus lens is decelerated to a preset speed, then moved at a constant speed through a constant speed section, and then stopped; and a second stop control method in which the focus lens is continuously decelerated and stopped without passing through a constant speed section. A focusing control device according to any one of supplementary items 1 to 10. [Additional Note 12] Furthermore, the camera has two continuous shooting modes: a continuous shooting interval priority mode that maintains a constant interval between consecutive shots, and a focus priority mode that prioritizes focusing accuracy over the interval between consecutive shots. The processor When the focus priority mode is selected as the continuous shooting mode and the F-number of the optical system including the focus lens is equal to or less than a preset value, the first stop control method is selected. Item 12. A focusing control device according to item 11. [Additional Note 13] A focusing control device according to any one of claims 1 to 12, An imaging element; Imaging device. [Additional Note 14] A focusing control method for performing focusing control in each frame period during shooting, comprising: In the N-th frame period, a lens drive time for moving the focus lens to a first target focus position in the N+1-th frame period is predicted based on first time-series AF information including AF information obtained in the N-1-th frame period; selecting a focus lens driving method to be executed in the Nth frame period based on the predicted lens driving time; Focus control method. [Additional Note 15] A focusing control program that causes a processor to execute focusing control during each frame period of photography, predicting, in an N-th frame period, a lens drive time for moving the focus lens to a first target focus position in an N+1-th frame period based on first time-series AF information including AF information obtained in an N-1-th frame period; selecting a focus lens driving method to be executed in the Nth frame period based on the predicted lens driving time; A focusing control program that causes a processor to execute a process including the steps of: [Explanation of symbols]

[0135] 10. Imaging device 11 Main unit 11A Camera side mount 11B Electrical contacts 12 Imaging lens 12A Lens side mount 12B Electrical Contact 13 Operating device 14 Finder 15 Display 20 Image sensor 20A light receiving surface 20B Imaging area 30 objective lenses 31 Focus Lens 32 Rear lens 34 Lens drive control unit 40 processors 42 memory 43 Programs 50 Main control unit 51 Imaging control unit 52 Image processing section 53 Display control unit 54 Area setting section 55 AF control section 56 Phase difference pixel signal acquisition unit 57 AF calculation unit 61 AF information recording unit 62 Focus position prediction unit 63 Drive method selection section 64 Object detection unit A optical axis BL Block C1,C2 correlation curve CF color filter CVS constant speed section D Image signal DF, DF1, DF2 Defocus amount Dp phase difference image signal EP,EP1,EP2 Exit pupil FP focus position FPT, FPT1, FPT2 target focus position IP1 1st image IP2 2nd image LDT lens operating time LF luminous flux ML Micro Lens N imaging pixels P1, P2 Phase difference detection pixels PD photodiode RA AF Area RL line S1, S2 subject STM, STM1, STM2 drive start timing signal T time TH threshold TS Time series AF information VL speed

Claims

1. A focusing control device that performs focusing control during each frame period of shooting, It has a processor, The processor, In an N-th frame period, a lens drive time for moving a focus lens to a first target focusing position in an N+1-th frame period is predicted based on first time-series AF information including AF information obtained in an N-1-th frame period; selecting a method of driving the focus lens to be executed in the N-th frame period based on the predicted lens driving time; Focus control device.

2. The processor, When the lens drive time is longer than a threshold value, a first drive method is selected as the drive method, in which the drive of the focus lens is started toward the first target focus position at a timing in which focus control in the N+1th frame period is completed in time. The focus control device according to claim 1 .

3. The processor, When the lens drive time is longer than a threshold value, a first drive method is selected as the drive method, in which the drive of the focus lens is started toward the first target focusing position before the AF information of the Nth frame period is acquired. The focus control device according to claim 1 .

4. The processor, When the lens drive time to the first target focus position is equal to or less than a threshold value, a second drive method is selected as the drive method, which predicts a second target focus position for the (N+1)th frame period based on second time-series AF information including AF information for the Nth frame period, and starts driving the focus lens toward the predicted second target focus position. The focus control device according to claim 1 .

5. The processor, When the lens drive time to the first target focus position is equal to or less than a threshold value, a second drive method is selected as the drive method, which predicts a second target focus position for the (N+1)th frame period based on second time-series AF information including AF information for the Nth frame period, and starts driving the focus lens toward the predicted second target focus position. The focusing control device according to claim 2 .

6. The AF information is information acquired using a phase difference detection pixel arranged in an imaging area of ​​an imaging element. The focus control device according to claim 1 .

7. When an AF area for acquiring the AF information is set in an imaging area, The processor, Obtaining information regarding reading of an image from an imaging element including the imaging region; determining a readout state of the image corresponding to the AF area based on the information; when it is determined that the readout of the image corresponding to the AF area is completed, a prediction of the second target focusing position is started. The focusing control device according to claim 4 .

8. AF information used for the first time-series AF information is acquired based on a main image captured once in each of the frame periods. The focus control device according to claim 1 .

9. AF information used for the first time-series AF information is acquired based on a live view image captured in each of the frame periods. The focus control device according to claim 1 .

10. the live view image is a latest live view image among a plurality of live view images captured in each of the frame periods; The focus control device according to claim 9 .

11. the focusing control is performed during continuous shooting in which main images are captured continuously over a plurality of frame periods while the release button is pressed; The focus control device according to claim 1 .

12. As a stop control method for stopping the focus lens during movement, there are provided two stop control methods, namely, a first stop control method for decelerating the focus lens to a preset speed, and then stopping the focus lens through a constant speed section in which the focus lens moves at a constant speed, and a second stop control method for continuously decelerating the focus lens and stopping the focus lens without passing through the constant speed section. The focus control device according to claim 1 .

13. Furthermore, the camera has two continuous shooting modes: a continuous shooting interval priority mode that keeps the continuous shooting interval constant, and a focus priority mode that prioritizes the accuracy of focusing over the continuous shooting interval. The processor, When the focus priority mode is selected as the continuous shooting mode and the F-number of an optical system including the focus lens is equal to or smaller than a preset value, the first stop control method is selected. The focus control device according to claim 12.

14. A focusing control device according to any one of claims 1 to 13, An imaging element; Imaging device.

15. A focusing control method for performing focusing control in each frame period during shooting, comprising: In an N-th frame period, a lens drive time for moving a focus lens to a first target focusing position in an N+1-th frame period is predicted based on first time-series AF information including AF information obtained in an N-1-th frame period; selecting a method of driving the focus lens to be executed in the N-th frame period based on the predicted lens driving time; Focus control method.

16. A focusing control program for causing a processor to execute focusing control during each frame period of shooting, predicting, in an N-th frame period, a lens drive time for moving the focus lens to a first target focusing position in an N+1-th frame period based on first time-series AF information including AF information obtained in an N-1-th frame period; selecting a method of driving the focus lens to be executed in the N-th frame period based on the predicted lens driving time; A focusing control program that causes a processor to execute a process including the steps of:

Images