JP6139960B2 - Imaging apparatus and control method thereof - Google Patents

Description

The present invention relates to an imaging apparatus and a control method therefor, and more particularly to a focus detection technique based on imaging plane phase difference AF.

  In recent years, an imaging apparatus represented by a single-lens reflex camera has been frequently photographed while viewing a live view (LV) screen (hereinafter referred to as LV photographing). It is demanded.

There are a phase difference detection method and a contrast detection method as main automatic focus detection (autofocus: AF) methods of the imaging apparatus.
In the phase difference detection method, the defocus amount of the imaging optical system is determined from the phase difference between a pair of image signals obtained by imaging light beams from a subject that has passed through different exit pupil regions in the imaging optical system on a pair of line sensors. Ask. When the focus lens is moved by an amount corresponding to the defocus amount, the imaging optical system is in focus on the subject (see Patent Document 1). However, when a light beam is imaged on the phase difference detection line sensor, a general configuration in which the optical path to the image sensor is blocked cannot perform focus detection by the phase difference detection method while performing LV imaging.

On the other hand, in the contrast detection method, an in-focus state is obtained by searching for a focus lens position where a contrast evaluation value generated from an image pickup signal obtained using an image pickup element is maximized (see Patent Document 2). The contrast detection method is suitable for AF at the time of LV photographing because focus detection is performed based on the imaging signal, and is the most mainstream AF method at the time of LV photographing in recent years. However, the contrast detection method cannot easily determine the position and direction in which the focus lens is moved to focus on the subject. For this reason, the contrast detection method may require time for focusing, may cause the focus lens to move in the wrong direction, or may pass through the focus position. In particular, at the time of moving image shooting, an image shot while the focus lens is moving is also recorded. Therefore, the moving time and moving operation of the focus lens up to the in-focus state affect the image quality of the recorded moving image.

Therefore, in AF control during moving image shooting, a high-quality focus detection operation that has a small influence on a recorded image is required rather than a speed (responsiveness) until a focused state is reached. For this reason, an imaging plane phase difference detection method has been proposed as a method capable of high-quality focus detection operation even during LV shooting. The imaging surface phase difference detection method is a method for obtaining a defocus amount based on a phase difference between a pair of signals obtained from an imaging element.

As a method for realizing the imaging surface phase difference detection method, a method has been proposed in which the imaging pixel of the imaging element is pupil-divided by a microlens and light is received by a plurality of focus detection pixels to detect the defocus amount simultaneously with imaging. Yes. In Patent Document 3, each photodiode is configured to receive light from a different pupil plane of an imaging lens by dividing photodiodes collected by one microlens in one pixel. Has been. This makes it possible to detect the focus by the imaging plane phase difference detection method from the outputs of the two photodiodes. By using the imaging surface phase difference detection method, it is possible to obtain the defocus amount and know the moving direction and the moving amount of the focus lens even during LV shooting, so that the focus lens can be moved at high speed and with high quality. . One of the advantages of performing LV shooting with the imaging plane phase difference detection method is that the defocus amount can always be detected, so even in scenes where the subject distance changes continuously, such as when the subject approaches or moves away, It is excellent in the followability of the focused state with respect to the movement.

  In Patent Document 4, a plurality of image shift amounts detected using a plurality of line sensors are held, and when a difference between a plurality of image shift amounts obtained at the time of focus detection exceeds a threshold value, a plurality of image shift amounts are stored. There has been proposed a method for calculating an image shift amount using any one of the shift amounts and a plurality of past image shift amounts.

Japanese Patent Laid-Open No. 09-054242 JP 2001-004914 A JP 2001-083407 A JP 2012-242613 A

In Patent Document 4, if the difference between a plurality of image shift amounts detected simultaneously is small, it is determined that the reliability of the image shift amount is high, and focus detection is performed based on these image shift amounts, thereby improving the stability of focus detection control. Can be increased. On the other hand, if it is determined that there is a large difference between the plurality of increase deviation amounts and the reliability of the image deviation amount is low, focus detection is performed in consideration of the image deviation amounts detected in the past, for example, a continuous distance change. Focus detection control can be performed with emphasis on the ability to follow a certain subject.

  However, in the imaging device described in Patent Document 4, when the difference between the detected image shift amounts is small, it is determined that the subject is stable. Then, the focus lens is temporarily stopped until it is determined that the focus level of the subject is reduced and it is necessary to perform focus detection again.

  For this reason, for example, if it is determined that the difference in image shift amount with respect to the approaching subject is small, the focus lens is temporarily stopped and restarted as shown in FIG. Then, the state of blurring is repeated. When such an image is displayed as an LV image, the appearance is not good. If such a phenomenon occurs during moving image shooting, the quality of the recorded moving image is not preferable.

  Further, as in the imaging device described in Patent Document 4, a configuration in which a plurality of image shift amounts are simultaneously detected and stored by a plurality of line sensors increases the circuit scale and processing load necessary for focus detection. Note that the focus lens may be temporarily stopped if it is determined that the subject is stable based on the size of one image shift amount instead of the difference between a plurality of image shift amounts. ) Will occur.

An object of the present invention is to improve the quality of a focus detection operation using an imaging surface phase difference detection method in view of such problems of the conventional technology.

The above-described object is to detect a defocus amount of a photographing optical system based on an image signal acquired from an image sensor and used for focus detection by a phase difference detection method, and a focus lens included in the photographing optical system. and control means for controlling the drive, imaging conditions, predetermined includes a whether a determination unit detection accuracy of the defocus amount matches the condition to decrease, the control means in advance by the detectors When a defocus amount equal to or less than a predetermined amount is detected by a predetermined first plurality of times of defocus amount detection, the focus lens is drives and controls the drive of the focus lens so as to stop, when the photographing condition is determined to meet the condition, the first plurality of defocus amount detection, a predetermined amount less of Defoe If the scan amount is detected a second smaller predetermined number of times or more than several times, it is achieved by that imaging device to and controlling the drive of the focus lens so as to stop the driving of the focus lens.

With such a configuration, according to the present invention, it is possible to improve the quality of the focus detection operation using the imaging plane phase difference detection method.

1 is a block diagram illustrating an example of a functional configuration of an interchangeable lens camera as an example of an imaging apparatus according to an embodiment. The figure which shows the pixel structural example of a non-imaging surface phase difference detection system and an imaging surface phase difference detection system The flowchart which shows the imaging process in 1st Embodiment. The flowchart which shows the initialization process in 1st Embodiment The flowchart which shows the moving image shooting process in 1st Embodiment. The flowchart which shows the focus detection process in 1st Embodiment. The figure which showed typically an example of the focus detection range handled by the focus state detection process in 1st Embodiment, and a focus detection area | region. The figure which shows the example of the image signal obtained from the focus detection area | region shown in FIG. The figure which shows the example of a relationship between the shift amount and correlation amount of the image signal shown in FIG. FIG. 8 is a diagram showing an example of the relationship between the shift amount of the image signal and the correlation change amount ΔCOR shown in FIG. Flowchart showing the AF restart determination process in S508 of FIG. Flowchart showing the AF process in S507 of FIG. 12 is a flowchart showing the lens drive setting process in S804 of FIG. 12 is a flowchart showing the lens driving process in S805 of FIG. FIG. 14 is a flowchart showing search drive processing in S1004 of FIG. The flowchart which shows the drive direction setting process of S1102 of FIG. FIG. 12 is a flowchart showing focus stop determination processing in S802 of FIG. The flowchart which shows the focus stop threshold value setting process in S1301 of FIG. FIGS. 5A and 5B are diagrams schematically illustrating (a) a conventional focus lens driving operation and (b) a focus lens driving operation according to the first embodiment for a subject having a continuous distance change. Flowchart showing AF processing in the second embodiment of the present invention The flowchart which shows the focus stop determination process in the 2nd Embodiment of this invention. The block diagram which shows the function structural example of the lens interchangeable camera as an example of the imaging device which concerns on the 3rd Embodiment of this invention. The flowchart which shows the focus stop threshold value setting process in the 3rd Embodiment of this invention.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiment described below is merely an example, and the present invention is not limited to the configuration described in the embodiment.

(First embodiment)
FIG. 1 is a block diagram illustrating an example of a functional configuration of an interchangeable lens camera as an example of an imaging apparatus according to the first embodiment of the present invention.
The imaging apparatus according to the present embodiment includes a replaceable lens unit 10 and a camera body 20. The lens control unit 106 that controls the overall operation of the lens and the camera control unit 212 that controls the overall operation of the camera system including the lens unit 10 can communicate with each other through terminals provided on the lens mount.

  First, the configuration of the lens unit 10 will be described. The fixed lens 101, the diaphragm 102, and the focus lens 103 constitute a photographing optical system. The diaphragm 102 is driven by the diaphragm driving unit 104 and controls the amount of light incident on the image sensor 201 described later. The focus lens 103 is driven by the focus lens driving unit 105, and the focusing distance of the imaging optical system changes according to the position of the focus lens 103. The aperture driving unit 104 and the focus lens driving unit 105 are controlled by the lens control unit 106 to determine the aperture amount of the aperture 102 and the position of the focus lens 103. The positional relationship among the fixed lens 101, the diaphragm 102, and the focus lens 103 is not limited to the configuration shown in FIG. In addition, the fixed lens 101 and the focus lens 103 are each illustrated as a single lens, but may be a lens group including a plurality of lenses.

  The lens operation unit 107 is an input device group for the user to perform settings related to the operation of the lens unit 10 such as AF / MF mode switching, shooting distance range setting, camera shake correction mode setting, and the like. When the lens operation unit 107 is operated, the lens control unit 106 performs control according to the operation.

  The lens control unit 106 controls the aperture driving unit 104 and the focus lens driving unit 105 according to a control command and control information received from a camera control unit 212 described later, and transmits lens control information to the camera control unit 212. .

Next, the configuration of the camera body 20 will be described. The camera body 20 is configured to acquire an imaging signal from a light beam that has passed through the imaging optical system of the lens unit 10.
The image sensor 201 is composed of a CCD or a CMOS sensor. The light beam incident from the imaging optical system of the lens unit 10 forms an image on the light receiving surface of the image sensor 201, and is converted into a signal charge corresponding to the amount of incident light by a photodiode provided in a pixel arranged in the image sensor 201. The The signal charge accumulated in each photodiode is sequentially read out from the image sensor 201 as a voltage signal corresponding to the signal charge from a drive pulse output from the timing generator 215 in accordance with a command from the camera control unit 212.

The imaging device 201 of the present embodiment includes two photodiodes in one pixel, and generates an image signal used for automatic focus detection (hereinafter referred to as imaging plane phase difference AF) using an imaging plane phase difference detection method. Is possible. 2A schematically illustrates an example of a pixel configuration that does not correspond to the imaging surface phase difference AF, and FIG. 2B schematically illustrates an example of a pixel configuration that corresponds to the imaging surface phase difference AF. Here, in any case, it is assumed that a Bayer array primary color filter is provided. In the pixel configuration of FIG. 2B corresponding to the imaging surface phase difference AF, one pixel in FIG. 2A is divided into two in the horizontal direction, and AB two photodiodes (light receiving regions) are provided. Note that the division method illustrated in FIG. 2B is an example, and other methods may be used, or different division methods may be applied depending on the pixels.

  The light beam incident on each pixel is separated by a microlens and received by two photodiodes provided in the pixel, whereby two signals for imaging and AF can be acquired by one pixel. That is, signals (A, B) obtained by two photodiodes A, B (A pixel, B pixel) in a pixel are two image signals for AF, and an addition signal (A + B) is an imaging signal. is there. Note that the pair of image signals used in the imaging plane phase difference AF is also a plurality of A so that the pair of image signals used in the normal phase difference detection AF is generated by a pair of line sensors having a plurality of pixels. It is obtained from the output of a pixel and a plurality of B pixels. Based on the AF signal, an AF signal processing unit 204 (to be described later) performs a correlation operation on the two image signals to calculate an image shift amount and various types of reliability information.

  The CDS / AGC / AD converter 202 performs correlated double sampling for removing reset noise, gain adjustment, and signal digitization on the imaging signal and AF signal read from the imaging element 201. The CDS / AGC / AD converter 202 outputs the imaging signal to the image input controller 203 and the imaging surface phase difference AF signal to the AF signal processing unit 204.

  The image input controller 203 stores the imaging signal output from the CDS / AGC / AD converter 202 in the SDRAM 209 via the bus 21. The imaging signal stored in the SDRAM 209 is read out by the display control unit 205 via the bus 21 and displayed on the display unit 206. In the operation mode for recording the imaging signal, the imaging signal stored in the SDRAM 209 is recorded on the recording medium 208 by the recording medium control unit 207.

  The ROM 210 stores a control program executed by the camera control unit 212 and various data necessary for the control. The flash ROM 211 stores various setting information related to the operation of the camera body 20 such as user setting information. Yes.

  The AF signal processing unit 204 performs a correlation operation on the two image signals for AF output from the CDS / AGC / AD converter 202 to obtain an image shift amount, reliability information (two image coincidence degree, two image steepness degree, Contrast information, saturation information, scratch information, etc.). The AF signal processing unit 204 outputs the calculated image shift amount and reliability information to the camera control unit 212.

  The camera control unit 212 changes the setting of the AF signal processing unit 204 as necessary based on the image shift amount and reliability information obtained by the AF signal processing unit 204. For example, when the image shift amount is greater than or equal to a predetermined amount, a wide area for performing the correlation calculation is set, or the type of the band pass filter is changed according to the contrast information. Details of the correlation calculation will be described later with reference to FIGS. 7 to 9B.

  In the present embodiment, a total of three signals of the imaging signal and the two AF image signals are acquired from the imaging element 201, but the present invention is not limited to this method. Considering the load of the image sensor 201, for example, a total of two signals of an imaging signal and one AF image signal may be taken out, and the difference between the imaging signal and the AF signal may be used as another AF image signal.

  The camera control unit 212 performs control by exchanging information with each functional block in the camera body 20. The camera control unit 212 not only performs processing in the camera body 20, but also turns on / off the power, changes settings, starts recording, starts AF control, confirms recorded video, etc. according to input from the camera operation unit 214. The various camera functions operated by the user are executed. Further, the camera control unit 212 sends a control command / control information of the lens unit 10 to the lens control unit 106, and acquires information on the lens unit 10 from the lens control unit 106.

  The camera control unit 212 is, for example, one or more programmable processors, and implements the operation of the entire camera system including the lens unit 10 by executing a control program stored in the ROM 210, for example.

  The focus stop determination unit 213 represents a part of the function of the camera control unit 212, and determines whether or not the subject is currently focused. When it is determined that the focus is achieved, the focus stop determination unit 213 stops driving the focus lens 103 via the lens control unit 106 and the focus lens drive unit 105 in the lens unit 10. On the other hand, when it is determined that the in-focus state has not yet been achieved, the in-focus stop determining unit 213 does not stop driving the focus lens 103.

  Conventionally, a digital camera is mainly used for still image shooting, and a video camera is generally used for moving image shooting. However, in recent years, a demand for a moving image shooting function of a digital camera is increasing. When moving image AF control is performed, since the image is recorded even while the focus lens is being driven, the drive quality of the focus lens is particularly important. More specifically, it is important to drive the focus lens so that the image quality of the moving image to be shot, particularly the temporal variation in the degree of focus, is reduced.

  As one of the controls for improving the driving quality of the focus lens, as described in Patent Document 4, when it is determined that the subject is in focus, it is determined that it is necessary to perform focus detection again thereafter. There is a method of stopping the driving of the focus lens until it stops. For example, it is determined that it is necessary to perform focus detection again when the subject changes or the degree of focus falls below a threshold value.

  If the focus lens is continuously driven without being stopped even in a focused state, it is possible to avoid changing the focus position even though the focused subject is not changed. For example, when the shooting range moves slightly and a part where the defocus detection accuracy is likely to deteriorate, such as the low contrast part of the subject, or when another subject crosses between the focused subject and the imaging device, etc. Incorrect focus lens drive is likely to occur.

  If it is determined that the subject is in focus at the time of moving image shooting, the focus lens is stopped once, and if it is determined that the subject has changed, control is performed so that focusing is resumed, so that unnecessary focusing operation can be suppressed.

  However, if it is determined that the subject is in focus, the focus lens is in a stopped state until it is determined that focus detection is to be performed again, so it is determined that the subject whose distance has changed is in focus. If so, problems arise. For example, as shown in FIG. 19 (a), if the phase difference detected in a scene that is shooting an approaching subject is small and it is determined that the subject is in focus, the focus lens is temporarily stopped and restarted. Is repeated, and the state of being out of focus and being out of focus is repeated. When such an image is displayed as an LV image, the appearance is not good. If such a phenomenon occurs during moving image shooting, the quality of the recorded moving image is not preferable.

Therefore, in this embodiment, in order to realize a focus detection operation that smoothly follows the change in the subject distance during moving image shooting, the focus stop determination unit 213 determines not only whether the subject is in focus but also the current subject. Judgment is made as to whether or not the tracking is continued. Then, if the subject is continuously being tracked, control is performed so that the focus lens continues to be driven without stopping even if it is determined to be in focus. Details regarding the operation of the in-focus stop determination unit 213 will be described later with reference to a flowchart describing the control of the camera body 20.

Next, the operation of the camera body 20 will be described with reference to FIGS.
FIG. 3 is a flowchart showing the procedure of the photographing process of the camera body 20. In step S301, the camera control unit 212 performs initialization processing, and proceeds to step S302. Details of the initialization process will be described later with reference to FIG. In step S302, the camera control unit 212 determines whether the shooting mode of the camera body 20 is the moving image shooting mode or the still image shooting mode. If the shooting mode is the moving image shooting mode, the process proceeds to step S303. . In step S303, the camera control unit 212 performs moving image shooting processing, and proceeds to step S305. Details of the moving image shooting process in S303 will be described later with reference to FIG. If the still image shooting mode is selected in S302, the camera control unit 212 performs a still image shooting process in S304, and proceeds to S305. Details of the still image shooting process in S304 will be omitted.

  In step S305, which is performed after moving image shooting processing in S303 or still image shooting processing in S304, the camera control unit 212 determines whether the shooting processing has been stopped. If not, the process proceeds to S306 and stops. If so, the shooting process is terminated. When shooting processing is stopped, operations other than shooting, such as when the power of the camera body 20 is turned off through the camera operation unit 214, user setting processing of the camera, playback processing for checking captured images / moving images, etc. Is done. In step S <b> 306, the camera control unit 212 determines whether the shooting mode has been changed. If the shooting mode has not been changed, the process proceeds to step S <b> 301. Return processing. If the shooting mode has not been changed, the camera control unit 212 continues the processing of the current shooting mode. If the shooting mode has been changed, the processing of the changed shooting mode is performed after performing the initialization process in S301. I do.

  Next, the initialization process in S301 of FIG. 3 will be described with reference to the flowchart of FIG. In step S401, the camera control unit 212 sets various initial values of the camera and advances the process to step S402. The camera control unit 212 sets initial values based on information such as user settings and shooting modes at the time when shooting processing is started or when the shooting mode is changed. In S402 and S403, the camera control unit 212 initializes a flag used in this embodiment. In step S402, the camera control unit 212 turns off the focus stop flag and advances the process to step S403. In step S403, the camera control unit 212 turns off the search drive flag and ends the process.

  The focus stop flag that is initialized in S402 is turned on when it is determined that the camera is in focus during movie shooting and the lens is stopped, and is off when it is determined that the lens is not yet focused and the lens is driven. Has a value. The search drive flag initialized in S403 has an off value when the defocus amount detected by the imaging surface phase difference detection method is reliable when driving the lens, and an on value when the defocus amount is not reliable.

  When the defocus amount is reliable, not only when the accuracy of the defocus amount can be determined to be reliable, but also when the defocus direction is determined to be reliable, the reliability is higher than a certain degree. is there. For example, when it can be determined that the main subject is in focus or when it is already in focus. In such a state, the defocus amount is trusted, and the focus lens is driven based on the defocus amount.

  On the other hand, when the defocus amount is unreliable, the defocus amount and direction (for example, represented by the sign of the defocus amount) cannot be determined to be certain, that is, the reliability is lower than a certain level. is there. For example, there is a state where the defocus amount cannot be calculated correctly, such as when the main subject is greatly blurred. In this case, driving the focus lens with the defocus amount reliable affects the image quality of the captured video, so search drive (the focus lens is driven by a predetermined amount in a certain direction regardless of the defocus amount Search for driving).

  Next, the moving image shooting process in S303 of FIG. 3 will be described with reference to FIG. In steps S501 to S504, the camera control unit 212 performs control related to moving image recording. In step S501, the camera control unit 212 determines whether the moving image recording switch is turned on. If the moving image recording switch is turned on, the process proceeds to step S502. If not, the process proceeds to step S505. In step S502, the camera control unit 212 determines whether the moving image is currently being recorded. If the moving image is not being recorded, the moving image recording is started in step S503 and the process proceeds to step S505. If the moving image is being recorded, the moving image recording is performed in step S504. Stop and proceed to S505. In this embodiment, each time the moving image recording switch is pressed, the recording of the moving image is started and stopped. Recording is started and stopped by other methods such as using different buttons for starting and stopping the recording or using a changeover switch or the like. You may do.

  In step S505, the camera control unit 212 performs focus state detection processing, and advances the processing to step S506. The focus state detection process is a process of acquiring defocus information and reliability information for performing imaging plane phase difference AF by the camera control unit 212 and the AF signal processing unit 204, and details will be described later with reference to FIG. . In step S506, after the focus state detection process is performed in step S505, the camera control unit 212 determines whether the focus is currently stopped. If the focus is not stopped, the process proceeds to step S507. Advances the process to S508. Whether the focus is stopped can be determined by turning on / off the focus stop flag described above. In step S507, which is performed when it is determined that the in-focus state is not stopped in step S506, the camera control unit 212 performs AF processing and ends the moving image shooting processing. S507 performs AF control based on the information detected in S505, and details will be described later with reference to FIG. In S508, which proceeds when it is determined in S506 that the in-focus state is stopped, the camera control unit 212 performs AF restart determination and ends the moving image shooting process. In step S508, it is determined whether or not AF control is to be started again when the main subject has moved or changed since the in-focus state has been stopped. Details will be described later with reference to FIG.

  Next, the focus state detection process in S505 of FIG. 5 will be described with reference to FIG. First, in step S601, the AF signal processing unit 204 acquires a pair of image signals for AF from pixels included in an arbitrarily set focus detection range. Next, in S602, the AF signal processing unit 204 calculates a correlation amount between the acquired image signals. Subsequently, in S603, the AF signal processing unit 204 calculates a correlation change amount from the correlation amount calculated in S602. In step S604, the AF signal processing unit 204 calculates a focus shift amount from the correlation change amount. In step S <b> 605, the AF signal processing unit 204 calculates reliability indicating how reliable the amount of focus deviation is. These processes are performed for the number of focus detection areas existing in the focus detection range. In step S606, the AF signal processing unit 204 converts the focus shift amount into the defocus amount for each focus detection region. Finally, the AF signal processing unit 204 determines a focus detection area used for AF in S607, and ends the focus state detection process.

The focus state detection process described in FIG. 6 will be described in more detail with reference to FIGS. 7 to 9B.
FIG. 7 is a diagram schematically illustrating an example of a focus detection range and a focus detection region handled in the focus state detection process.
FIG. 7A shows an example of a focus detection range 1502 in the pixel array 1501 of the image sensor 201. The shift area 1503 is an area necessary for correlation calculation. Accordingly, a region 1504 obtained by combining the focus detection range 1502 and the shift region 1503 is a pixel region necessary for the correlation calculation. In the drawing, p, q, s, and t respectively represent coordinates in the x-axis direction, p and q represent the x-coordinates of the start point and end point of the pixel region 1504, and s and t represent the x and x of the start point and end point of the focus detection range 1502, respectively. Represents coordinates.

FIG. 7B is a diagram showing an example in which the focus detection range 1502 is divided into five focus detection areas 1505 to 1509. In the present embodiment, the focus shift amount is calculated for each focus detection region obtained by dividing the focus detection range in this way, and the most reliable focus shift amount is used.
FIG. 7C is a diagram showing a temporary focus detection area in which the focus detection areas 1505 to 1509 in FIG. 7B are connected. In this way, the amount of focus deviation calculated from the area where the focus detection areas are connected may be used. The arrangement of the focus detection area, the area size, and the like are not limited to the configuration illustrated here, and other configurations may be used.

FIG. 8 shows an example of an AF image signal acquired from the pixels included in the focus detection areas 1501 to 1509 set in FIG. The solid line 1601 is the image signal A, and the broken line 1602 is the image signal B.
FIG. 8A shows an example of the image signal before the shift.
FIGS. 8B and 8C show a state where the image waveform before the shift in FIG. 8A is shifted in the plus direction and the minus direction. When calculating the correlation amount, both the image signal A 1601 and the image signal B 1602 are shifted one bit at a time in the direction of the arrow. Next, a method for calculating the correlation amount COR will be described.

First, as shown in FIGS. 8B and 8C, each of the image signal A1601 and the image signal B1602 is shifted by 1 bit, and the sum of the absolute values of the differences between the image signal A and the image signal B at that time is calculated. calculate. At this time, the shift amount is represented by i, the minimum shift amount is ps in FIG. 8, and the maximum shift amount is qt in FIG. Further, x is the start coordinate of the focus detection area 1508, and y is the end coordinate of the focus detection area 1508. Using these, the correlation amount COR in the focus detection area 1508 can be calculated by the following equation (1).

  FIG. 9A shows an example of the relationship between the shift amount and the correlation amount. The horizontal axis indicates the shift amount, and the vertical axis indicates the correlation amount. Of the extreme values 1702 and 1703 in the correlation amount waveform 1701, the smaller the correlation amount, the higher the degree of coincidence between the image signal A and the image signal B. Next, a method for calculating the correlation change amount ΔCOR will be described.

First, the correlation change amount is calculated from the correlation amount difference of one shift skipping from the correlation amount waveform of FIG. The shift amount is represented by i, the minimum shift amount is ps in FIG. 8, and the maximum shift amount is qt in FIG. Using these, the correlation change amount ΔCOR can be calculated by the following equation (2).

  FIG. 10A shows an example of the relationship between the shift amount and the correlation change amount ΔCOR. The horizontal axis indicates the shift amount, and the vertical axis indicates the correlation change amount. In the correlation change amount waveform 1801, 1802 and 1803 are the vicinity where the correlation change amount becomes positive to negative. This is called a state zero cross where the correlation change amount is 0, and the degree of coincidence between the image signals is the highest, and the shift amount at the time of the zero cross becomes the focus shift amount.

続いて整数部分βは、図１０（ｂ）中より以下の式（４）によって算出することができる。
β＝ｋ−１ （４）
αとβの和からピントずれ量ＰＲＤを算出することができる。 FIG. 10B is an enlarged view of the portion 1802 in FIG. 10A, and 1901 is a part of the correlation variation waveform 1801. A method of calculating the focus shift amount PRD will be described with reference to FIG.
Here, the shift amount (k−1 + α) at the time of zero crossing is divided into an integer part β (= k−1) and a decimal part α. The decimal part α can be calculated by the following equation (3) from the similar relationship between the triangle ABC and the triangle ADE in the figure.

Subsequently, the integer part β can be calculated by the following formula (4) from FIG.
β = k−1 (4)
The focus shift amount PRD can be calculated from the sum of α and β.

以上のように、ゼロクロスが複数存在する場合は、急峻性によって第１のゼロクロスを決定する。続いてピントずれ量の信頼性の算出法について説明する。 Also, as shown in FIG. 10A, when there are a plurality of shift amounts that become zero crosses, the first zero cross is defined as a point where the steepness of the correlation amount change at the zero crosses is large. This steepness is an index indicating the ease of AF. The larger the value, the easier it is to perform AF. The steepness maxder can be calculated by the following equation (5).

As described above, when there are a plurality of zero crosses, the first zero cross is determined based on steepness. Next, a method for calculating the reliability of the focus shift amount will be described.

The reliability can be defined by the steepness described above and the matching degree fnclvl (hereinafter referred to as two-image matching degree) of the image signals A and B. The degree of coincidence of two images is an index representing the accuracy of the amount of focus deviation, and the smaller the value, the better the accuracy.
FIG. 9B is an enlarged view of the portion 1702 in FIG. 9A, and 2001 is a portion of the correlation amount waveform 1701. A method for calculating steepness and the degree of coincidence of two images will be described with reference to FIG.
The two-image coincidence degree fnclvl can be calculated by the following equation (6).

Next, the AF restart determination in S508 of FIG. 5 will be described using the flowchart of FIG. The AF restart determination is a process for determining whether to drive the focus lens 103 again when it is determined that the focus lens 103 is in focus and the focus lens 103 is stopped.
In step S701, the camera control unit 212 determines whether the defocus amount calculated by the AF signal processing unit 204 is smaller than a predetermined multiple (here, 1) of the focal depth. If the defocus amount is small, the process proceeds to step S702. The process proceeds to S704. In step S702, the camera control unit 212 determines whether the reliability calculated by the AF signal processing unit 204 is better than a predetermined value. If the reliability is higher, the process proceeds to step S703. If not, the process proceeds to step S704. . In step S703, the camera control unit 212 resets the AF restart counter, and advances the process to step S705. In step S704, the camera control unit 212 adds an AF restart counter and advances the process to step S705.

  As described above, when the defocus amount is greater than or equal to the predetermined amount or the reliability of the defocus amount is worse than the predetermined value, the camera control unit 212 determines that the main subject being shot has changed, and restarts AF. Preparation is made (re-driving the focus lens 103). On the other hand, when it is determined that the main subject has not changed from the size of the defocus amount and the reliability, the AF is not restarted (the stopped state of the focus lens 103 is maintained).

  The threshold value of the defocus amount set in S701 is set empirically or experimentally so that AF restart is performed when the main subject is changed, and AF restart is difficult when the main subject is not changed. Further, the reliability threshold value set in S702 is set such that AF restart is performed when the reliability is so low that it is difficult to trust the defocus direction, for example. As described above, the determinations in S701 and S702 can be said to be determination processing for determining whether or not the main subject has changed. Therefore, it can be replaced with an arbitrary process capable of the same determination, and the type and value of the threshold used according to the processing method are set.

  In step S705, the camera control unit 212 determines whether the value of the AF restart counter is greater than a predetermined value. If the value is larger than the predetermined value, the process proceeds to step S706, and if smaller, the AF restart determination process ends. In step S <b> 706, the camera control unit 212 restarts AF by turning off the focus stop flag, and ends the AF restart determination process. In determining AF restart in S706, the camera control unit 212 determines in S705 whether the value of the AF restart counter added in S704 is greater than a predetermined value. In the AF restart counter addition and value determination, the determination of whether or not the main subject has changed is not performed based on a single determination of the amount of defocus or the reliability. This is based on statistics. By doing this, it is determined that the main subject has changed due to a very temporary defocus amount or a change in reliability even though the main subject has not actually changed, and AF is restarted. Prevent impact on image quality.

Next, the AF process in S507 of FIG. 5 will be described using the flowchart of FIG. The AF processing is processing for driving the focus lens in a state where focusing is not stopped and for determining whether focusing is stopped.
In step S <b> 801, the camera control unit 212 determines whether the defocus amount is equal to or smaller than a predetermined amount (here, within the depth of focus) and whether the defocus amount reliability is better than a predetermined value. Judging. If this condition is met, the camera control unit 212 proceeds to step S802, and otherwise proceeds to step S803. In the present embodiment, the threshold used in S801 is set to be one time the focal depth, but it may be set larger or smaller as necessary. The reliability threshold value set in step S801 is set to a value that can guarantee at least the focusing accuracy.

  In step S <b> 802, the camera control unit 212 performs a focus stop determination process for determining whether to stop driving the focus lens when the subject is focused, and ends the AF process. In the focus stop determination process in S802, the camera control unit 212 determines whether to turn on or keep the focus stop flag on. Details of the focus stop determination process will be described later with reference to FIG.

  If the defocus amount is not within the depth of focus in S801 or if the reliability of the defocus amount is worse than the predetermined value, the camera control unit 212 resets the focus stop determination counter in S803 and advances the process to S804. The focus stop determination counter is data used to determine whether or not to stop driving the focus lens in the focus stop determination process in S802 described later. If the defocus amount is not within the depth of focus or if the reliability of the defocus amount is worse than a predetermined value, the focus stop determination counter is reset so that the focus stop determination is not performed immediately thereafter.

  In step S804, the camera control unit 212 determines and sets the driving speed and driving method of the focus lens. Details will be described later with reference to FIG. In step S805, which is performed after the lens drive setting is performed in step S804, the camera control unit 212 performs lens drive processing and ends the AF processing. Details of the lens driving process in S805 will be described later with reference to FIG.

Next, the lens drive setting in S804 of FIG. 12 will be described using the flowchart of FIG. In the lens driving setting in the present embodiment, the driving speed of the focus lens is set according to the reliability of the defocus amount.
In steps S901 to S907, the lens drive speed is set, and the search drive transition counter is added and reset. In S901, it is determined whether or not the reliability is better than the predetermined value α (whether the reliability is higher than the predetermined reliability). If the reliability is higher than the predetermined value α, the process proceeds to S902. If not, the process proceeds to S904. Proceed with the process. In step S902, the camera control unit 212 resets the search drive counter and advances the process to step S903, sets the lens drive speed A, and advances the process to step S908.

  When the reliability is not better than the predetermined value α in S901 (the reliability is not higher than the predetermined reliability), in S904, the camera control unit 212 adds the search drive transition counter and advances the process to S905. In step S905, the camera control unit 212 determines whether the value of the search drive transition counter is equal to or greater than a predetermined value. If it is equal to or greater than the predetermined value, the process proceeds to step S906. In step S906, the camera control unit 212 turns on the search drive flag and proceeds to step S908 when the process proceeds to step S906 when it is determined in step S905 that the value of the search drive transition counter is greater than or equal to the predetermined value. On the other hand, when it is determined in S905 that the value of the search drive transition counter is not equal to or greater than the predetermined value, the camera control unit 212 proceeds to S908 after setting the focus lens drive speed Z in S907. In S908 performed after any of S903, S906, and S907, the camera control unit 212 determines whether or not the search drive flag is on. If it is on, the camera control unit 212 proceeds to S909, and if it is off, the lens drive setting process. Exit. In S909, which proceeds after determining that the search drive flag is on in S908, the camera control unit 212 sets the lens drive speed S and ends the lens drive setting process.

The reliability threshold value α set in S901 is set to a value at which at least the direction can be determined to be reliable out of the defocus direction and amount. When the defocus direction is reliable, the focus lens is driven based on the defocus amount at the set lens driving speed A. On the other hand, when the reliability that is determined that the defocus direction is not reliable (which is worse than α) continues, search driving is performed. Search drive is a method of setting the defocus direction and driving the focus lens within the drive range by a predetermined unit (step drive amount) in that direction regardless of the defocus amount.

  If the direction of the defocus amount is also unreliable in S901, the search drive transition counter is added in S904, and it is determined whether or not the value of the search drive transition counter is equal to or greater than a predetermined value in S905. Search drive is performed only when the state is low. As described above, since the search drive does not use the defocus amount, there is a possibility of driving a poor-quality focus lens that temporarily becomes largely blurred. Therefore, even if the reliability is lowered, the search drive is not immediately shifted to prevent the search drive from being inadvertently caused by temporary factors such as noise.

  When it is determined in S905 that the value of the search drive shift counter becomes equal to or greater than the predetermined value and shifts to search drive, the camera control unit 212 turns on the search drive flag in S906, and in S909, the lens drive speed for search drive is set in S909. Set S. The search drive speed S is set to a value faster than the drive speed A. If the reliability of the defocus amount becomes better than the predetermined value α before the search drive shift counter reaches the predetermined value, the camera control unit 212 resets the search drive shift counter in S902. Further, although the reliability of the defocus amount is worse than the predetermined value α, the lens drive speed Z set in S907 that is advanced when the value of the search drive transition counter has not reached the predetermined value is slower than the drive speed A, and Set a sufficiently slow value (including zero).

The lens driving speed set in FIG. 13 has the following relationship.
Z <A <S (Z is the slowest, S is the fastest)
Search driving is performed when the reliability of the defocus amount is low and the defocus direction is unreliable, and the main subject is considered to be greatly blurred. For this reason, the focus lens driving speed S at the time of search driving set in S909 is set to a value faster than the driving speed A so that focusing can be performed quickly.

  In S901, the reliability is lower than the predetermined value α, and it is better not to drive the focus lens by believing in the defocus amount while determining whether to shift to search driving in S905. Therefore, in S907, the camera control unit 212 sets the driving speed Z of the focus lens to a speed 0 (stop) or a low speed that does not make the driving conspicuous. As a result, it is possible to prevent the focus lens from being driven with poor quality when the defocus amount reliability is poor.

Next, the lens driving process in S805 of FIG. 12 will be described using the flowchart of FIG. The lens driving process is a process for driving the focus lens 103 based on the driving speed set by the lens driving setting process described with reference to FIG.
In step S1001, the camera control unit 212 determines whether the search drive flag is off. If the search drive flag is off, the process proceeds to step S1002, and the focus lens is driven at the drive speed set by the lens drive setting process based on the defocus amount. Then, the lens driving process ends. If the search drive flag is on, the process proceeds to S1003, the search drive process is performed, and the lens drive process ends. Details of the search driving process in S1003 will be described later with reference to FIG.

  Next, the search drive processing in S1003 of FIG. 14 will be described using the flowchart of FIG. The search drive process is a process that is performed when the search drive flag is turned on in S906 of FIG. 13, and the focus lens drive range is driven at the drive speed set in S909.

  In step S1101, the camera control unit 212 determines whether or not the search drive is the first time. If it is not the first time, the process proceeds directly to step S1103. If it is the first time, the drive direction is set in step S1102, and then the process proceeds to step S1103. When the search drive is the first time, it is necessary to determine which of the focus lenses 103 is driven. The drive direction setting process in S1102 will be described later with reference to FIG.

  In step S <b> 1103, the camera control unit 212 drives the focus lens 103 with the set driving direction and driving speed S through the lens control unit 106, and advances the process to step S <b> 1104. In step S1104, the camera control unit 212 determines whether the focus lens 103 has reached the near end or the infinite end. If it has reached, the process proceeds to step S1105, and if not, the process proceeds to step S1106. In step S1105, the camera control unit 212 reverses the driving direction and advances the process to step S1106. In step S1106, the camera control unit 212 determines whether the reliability is a value better than the predetermined value α. If the reliability is higher than the predetermined value α, the process proceeds to step S1107. If not, the process proceeds to step S1108. In step S1108, the camera control unit 212 determines whether the focus lens 103 has reached both the near end and the infinite end during the search driving process. If the focus lens 103 has reached, the process proceeds to step S1107. The search driving process ends. In step S1107, the camera control unit 212 turns off the search drive flag and ends the search drive process.

  The conditions for terminating the search drive are when the reliability becomes better than the predetermined value α in S1106, or when the focus lens 103 reaches both the closest end and the infinite end in S1108. The reliability threshold value α set in step S1106 is the same as the threshold value α set in step S901 in FIG. 13, and is a value with which at least the defocus amount direction can be determined to be reliable. If the reliability is better than the threshold value α, it can be determined that the subject is approaching the in-focus state, so the search drive is stopped and the control is switched to drive based on the defocus amount again. If it is determined in S1108 that both the near end and the infinite end have been reached, the entire focus drive range is driven, that is, the subject cannot be specified. In this case, the search drive flag is turned off to return to the initial processing state. If the subject cannot be specified, the search drive may be continued without turning off the search drive flag.

  Next, the drive direction setting process in S1102 of FIG. 15 will be described using the flowchart of FIG. In step S1201, the camera control unit 212 determines whether the current position of the focus lens 103 is closer to the closest end than the infinite end. If the current position of the focus lens 103 is closer to the close end, the process proceeds to step S1202. Proceed to the process.

  In step S1202, the camera control unit 212 sets the driving direction of the focus lens 103 at the start of search driving to the closest direction, and ends the driving direction setting process. On the other hand, in S1203, the camera control unit 212 sets the driving direction of the focus lens 103 at the start of search driving to an infinite direction, and ends the driving direction setting process. By setting the drive direction in this way, it is possible to shorten the time for searching and driving the entire focus lens drive region, and to shorten the maximum time required to find the subject by the search drive.

Next, the focus stop determination process performed in S802 of FIG. 12 will be described using the flowchart shown in FIG.
In step S1301, the camera control unit 212 (focus stop determination unit 213) sets a focus stop threshold used to determine whether to stop driving the focus lens, and advances the process to step S1302. Details of the focus stop threshold value setting process in S1301 will be described later with reference to FIG.

  In step S1302, the focus stop determination unit 213 adds 1 to the value of the focus stop counter and advances the process to step S1303. In step S1303, the focus stop determination unit 213 determines whether the value of the focus stop counter is equal to or greater than the focus stop threshold set in step S1301. If the focus stop threshold is equal to or greater than the focus stop threshold, the process proceeds to step S1304. If there is, the process is terminated. In step S1304, the focus stop determination unit 213 turns on the focus stop flag and ends the process.

  The value set as the focus stop threshold value in S1301 will be described later with reference to FIG. 18, but in the description of FIG. 17, it is assumed that a value of 2 or more is set as the focus stop threshold value. The value of 2 or more corresponds to the focus stop threshold Y set in S1404 of FIG. 18 in the present embodiment. In the present embodiment, the focus stop threshold is a threshold of the number of times that the defocus amount reliability is continuously determined to be better than α.

  As described above, in the moving image AF control, the driving of the focus lens is stopped when it is determined that the subject is in focus, in order to suppress unnecessary fluctuation of the focus level due to a temporary factor. However, as described with reference to FIG. 19A, if it is determined that the subject is in focus while following the subject whose distance is gradually changing and the focus lens is stopped, the process of S508 in FIG. The focus lens is not driven until it is determined to restart in the startup determination process. Until the restart is determined, the subject's blur gradually increases, and when the restart is determined and the focus lens is redriven, the subject is focused. Stopped. As a result, as shown in FIG. 19A, the focus lens is repeatedly driven, stopped, and restarted, and a moving image that repeats the behavior of being out of focus when the subject is in focus is captured.

  Therefore, in this embodiment, even when the defocus amount is within the depth of focus and the reliability of the defocus amount is better than a predetermined value, it is determined that the in-focus state is satisfied and the driving of the focus lens is stopped immediately. Without continuing, the focus lens continues to be driven. Then, when the determination that the defocus amount is within the depth of focus and the reliability of the defocus amount is better than a predetermined value continues for a predetermined number of times, the driving of the focus lens is stopped. Note that it is not essential whether the reliability is better than a predetermined value, and it may be determined only whether the defocus depth is within the focal depth.

  If the subject has a gradually changing distance, even if the defocus amount falls within the depth of focus at a certain point in time, the defocus amount deviates from the depth of focus over time. Therefore, it is determined that the distance to the subject is stable (focused) for the first time only when the defocus amount is within the depth of focus continuously for a predetermined number of times, and driving of the focus lens is stopped.

  That is, if the defocus amount is not within the depth of focus in S801 of FIG. 12, the focus stop counter is reset in S803. Therefore, even if the defocus amount falls within the depth of focus, the defocus amount deviates from the focus depth before the value of the focus stop counter reaches the focus stop threshold (or the reliability of the defocus amount exceeds the predetermined value). When it gets worse), the focus stop counter is reset. During this time, since the focus lens continues to be driven, the focus lens can be driven to follow the latest subject distance even when the subject distance changes. Accordingly, even for a subject as shown in FIG. 19A, the focus lens can be driven smoothly and following the subject distance as shown in FIG. The in-focus level is not greatly changed.

  Next, the focus stop threshold value setting process in S1301 of FIG. 17 will be described using the flowchart of FIG. In step S1401, the camera control unit 212 (focus stop determination unit 213) determines whether the image height of the focus detection area (AF frame) set in step S607 in FIG. 6 is greater than a predetermined value. The focus stop determination unit 213 advances the process to S1402 when it is determined that the image height of the focus detection area is greater than the predetermined value, and proceeds to S1403 when it is determined that the image height is less than the predetermined value.

  In step S1403, the focus stop determination unit 213 determines whether the set aperture value is smaller than the predetermined value (larger than the predetermined value). If it is determined that the aperture value is smaller, the process proceeds to step S1402. If it is determined, the process proceeds to S1404. In step S1402, the in-focus stop determination unit 213 sets the in-focus stop threshold value to X and ends the process. In step S1404, the focus stop determination unit 213 sets the focus stop threshold value to Y (Y> X) and ends the process.

  In the description of FIG. 17, it has been described that the focus stop threshold value is set to 2 or more, but this assumes Y that is set as the focus stop threshold value in S1404. By setting the focus stop threshold to 2 or more (an integer thereof), focus stop can be performed only when the defocus amount within the depth of focus is continuously observed in S1303 of FIG.

  However, in the present embodiment, when the image is shot with a setting that causes the defocus detection accuracy to deteriorate, the focus stop threshold is set to X (X <Y) in S1402. Here, as an example of the setting that the defocus detection accuracy deteriorates, (1) when the image height of the focus detection area is large, (2) when the aperture value is large (small aperture) is shown.

  The imaging surface phase difference detection method generally has a characteristic that the larger the image height, the greater the difference in the amount of light incident on the pupils A and B that acquire the image signals A and B, and the pupil intensity varies depending on the position in the pupil. . Therefore, the level difference between the image signals A and B appears remarkably at a position where the image height is large, the image coincidence between the image signals A and B is lowered, and the defocus detection accuracy is lowered.

  In the imaging surface phase difference detection method, the larger the aperture value (small aperture), the shorter the baseline length for imaging the image signals A and B. Therefore, the image shift amount of the image signals A and B is set to the defocus amount. There is a characteristic that the conversion factor to be converted becomes large. Therefore, the larger the aperture value (small aperture), the smaller the image shift amount is converted into a larger defocus amount, and the defocus accuracy is deteriorated.

  In the present embodiment, X set to the focus stop threshold value in S1402 is set to 1. This is because, under conditions where the defocus detection accuracy is poor, it may be difficult to continuously satisfy the defocus amount and the reliability conditions in S801 even when the distance of the subject does not change. If the focus stop threshold is set to a large value under conditions where the defocus detection accuracy is poor, the focus lens will not be determined even though the subject distance has not changed, and the focus lens will continue to be driven. It repeats. For this reason, in the present embodiment, when the condition that the defocus detection accuracy (reliability) tends to be low is set, if the defocus amount is within the depth of focus and the reliability is better than a predetermined value even once. Immediately, the focus lens is determined to be in focus and the driving of the focus lens is stopped. Here, as an example, X is 1 and Y is 2 or more, but any other combination of values may be used as long as X <Y.

  Note that the aperture value and the image height have been described as examples of conditions under which defocus detection accuracy (reliability) tends to be low, but other conditions may be considered in addition to or instead of these. For example, instead of the aperture value, the condition that the value of the conversion coefficient is a predetermined value or more may be used as a condition. This is because the size of the aperture value and the size of the conversion coefficient are linked as described above. Similarly, other parameters having a magnitude linked to a change in the magnitude of the transform coefficient can be used. In addition, parameters independent of the conversion coefficient and the image height can be considered.

  In S801, it is determined whether both the defocus amount and its reliability satisfy the condition. If the defocus detection accuracy is set to deteriorate, is the defocus depth within the focus depth? It may be modified so as to determine only whether or not. In this case, the same determination as S1401 and S1403 is performed before S801, and if either of them is satisfied, only the determination of the defocus amount may be performed in S801.

  In the case of AF control during still image shooting, since it is important that the time until focusing is short, the stage of detecting the defocus amount within a range in which focusing accuracy is guaranteed (a predetermined multiple of the depth). Thus, the drive of the focus lens is stopped immediately after the focus lens is driven.

As described above, in the present embodiment, when the defocus amount within the depth of focus is detected, it is determined that the focus is in focus immediately, and driving of the focus lens is not stopped, but the defocus amount within the depth of focus is determined. When it is continuously detected a predetermined number of times or more, the driving of the focus lens is stopped. As a result, even when shooting a subject whose distance is gradually changing, focus detection that smoothly follows the subject distance without changing the focus state of the captured image greatly, that is, quality A good focus lens can be driven.

  In addition, when the imaging surface phase difference detection method is used, if the defocus detection accuracy is set to deteriorate, the condition for stopping the driving of the focus lens is compared to the case where such setting is not made. Set loosely. In this way, it is possible to prevent the focus lens from being unable to stop driving even though the distance to the subject has not changed.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described. First, differences between the present embodiment and the first embodiment will be described.
In the first embodiment, the driving of the focus lens is stopped when the defocus amount within the depth of focus is continuously detected a predetermined number of times. In the second embodiment, if the defocus amount within the depth of focus is detected a plurality of times (not more than a predetermined number of times) by a plurality of consecutive predetermined defocus amount detections, the driving of the focus lens is stopped. Control to do.

Since the configuration of the interchangeable lens camera including the lens and the camera body in the present embodiment is the same as that described in the first embodiment with reference to FIG.
Since the operation of the camera body 20 described in the first embodiment with reference to the flowcharts of FIGS. 3 to 6 and FIGS. 11 to 18 is the same in this embodiment, the description thereof is omitted.

  First, the AF processing in S507 of FIG. 5 will be described using the flowchart of FIG. The processes in S2301, S2304, and S2305 in FIG. 20 are the same as the processes in S801, S804, and S805 in FIG. In S2301, the camera control unit 212 (focus stop determination unit 213) executes focus stop in S2302, which is executed when it is determined that the defocus amount is within the depth of focus and the reliability of the defocus amount is better than a predetermined value. A determination is made and the AF process is terminated. Details of the focus stop determination process will be described later with reference to FIG. The camera control unit 212 shifts the focus stop transition determination flag to the left in S2303, which is executed when it is determined in S2301 that the defocus amount is not within the depth of focus or the reliability of the defocus amount is worse than the predetermined value. Then, the process proceeds to S2304. In the first embodiment, the focus stop determination counter is used to perform the focus stop determination, but in this embodiment, the focus stop transition determination flag is used.

Next, details of the focus stop determination process performed in S2302 of FIG. 20 will be described using the flowchart of FIG.
Since S2401 and S2405 in FIG. 21 are the same as the processes in S1301 and S1304 in FIG. In step S2402, which is executed after the focus stop threshold value is set in step S2401, the focus stop determination unit 213 shifts the focus stop transition determination flag to the left and advances the process to step S2403. In step S2403, the focus stop determination unit 213 sets the least significant bit of the focus stop transition determination flag to 1, and advances the process to step S2404. In step S2404, the in-focus stop determination unit 213 determines whether the in-focus stop transition determination flag has a bit “1” that is equal to or greater than the number of in-focus stop thresholds set in step S2401. The stop flag is set to 1 and the focus stop determination process is terminated. When it is determined that the number of bits of “1” included in the focus stop transition determination flag is less than the focus stop threshold, the focus stop determination unit 213 ends the focus stop determination process without executing S2405. . Note that the determination in S2404 is performed by determining whether the ratio and probability of the “1” bit with respect to the total number of bits of the in-focus stop transition determination flag is greater than or equal to a predetermined value, and the length of the period during which the defocus amount within the focal depth is detected Other determination methods such as determination of whether (time) is equal to or longer than a predetermined time may be used.

  In this embodiment, the number of bits of “1” included in the focus stop transition determination flag is used instead of the counter value as an object to be compared with the focus stop threshold. The focus stop transition determination flag is shifted to the left by 1 bit each time S2402 in FIG. 21 and S2303 in FIG. 20 are executed, that is, every time AF processing in FIG. 20 is performed. On the other hand, only when the detected defocus amount is within the depth of focus and the reliability is better than a predetermined value, the least significant bit of the focus stop transition determination flag is set to “1” in S2403. Therefore, if the focus stop transition determination flag is n bits (n is an integer greater than 1), the number of bits of “1” that the focus stop transition determination flag has after executing AF processing n times is n times. This is equal to the number of times that a defocus amount within the depth of focus and whose reliability is better than a predetermined value is detected. Therefore, even if the focus is not continuous, if the defocus amount within the depth of focus and the reliability better than the predetermined value is detected the number of times equal to or greater than the focus stop threshold, the focus lens is stopped in this embodiment. It is necessary to set the number of bits n of the determination flag to be larger than the focusing stop threshold. When the number of bits n = the focus stop threshold value, the same control as in the first embodiment can be performed.

  In the present embodiment as well, as in the first embodiment, a small focus stop threshold is set when a predetermined condition for reducing the detection accuracy of the defocus amount is met, and the subject distance is not changed. Therefore, the drive of the focus lens is prevented from continuing. However, in this embodiment, since it is easier to determine that the driving of the focus lens is stopped than in the first embodiment, hunting occurs under shooting conditions in which the defocus detection accuracy decreases even if the focus stop threshold is constant. Can be suppressed. For example, an effect of suppressing the occurrence of hunting under a shooting condition in which defocus detection accuracy that is not easy to set in advance, such as a low-contrast subject or a change in brightness of the subject, is expected.

  Note that the determination method of the first embodiment and the determination method of the present embodiment may be used in combination. In this case, the determination method of the first embodiment can be realized by determining the number of consecutive “1” bits of the focus stop transition determination flag. In addition, there is no particular limitation on the switching condition between the determination method of the first embodiment and the determination method of the present embodiment. For example, when the determination method of the first embodiment is used, the focus lens is continuously used. When the driving time exceeds a predetermined time, it is possible to switch to the determination method of the present embodiment.

As described above, in the present embodiment, when the defocus amount within the depth of focus is detected, it is determined that the focus is in focus immediately, and driving of the focus lens is not stopped, but the defocus amount within the depth of focus is determined. When the predetermined ratio or more is detected, the driving of the focus lens is stopped. Even with this method, even when shooting a subject whose distance is gradually changing, focus detection that smoothly follows the subject distance without greatly changing the focus state of the captured image, that is, It is possible to drive a focus lens of good quality. In particular, the method of the first embodiment is more suitable for the effect of suppressing the occurrence of hunting under the condition that the defocus detection accuracy is lowered.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the present embodiment, when the lens unit 10 is a zoom lens with a variable focal length (view angle), the focus determination for stopping the driving of the focus lens according to the focal length (view angle) of the lens unit 10 is performed. It is characterized by changing conditions.

  FIG. 22 is a block diagram illustrating a functional configuration example of an interchangeable lens camera as an example of an imaging apparatus according to the third embodiment of the present invention. In FIG. 22, the configuration of the camera body 20 is the same as that in FIG. In addition, the lens unit 30 of FIG. 22 includes a zoom lens 302, a second fixed lens 304, and a zoom lens driving unit 306 in addition to the lens unit 10. The zoom lens 302 and the second fixed lens 304 are each shown as a single lens, but may be a lens group including a plurality of lenses.

  The lens control unit 309 controls the position of the zoom lens 302 via the zoom lens driving unit 306 when the zoom lens is operated by the operation of the lens operation unit 310, and the focal length (angle of view) of the lens unit 30 is controlled. change. In addition, the lens control unit 309 acquires focal length information of the lens unit 30 from the zoom lens driving unit 306 and transmits lens control information including this to the camera control unit 212. In addition to the functions described above, the lens control unit 309 and the lens operation unit 310 also have the functions described with reference to FIG. 1 in the first embodiment.

  Thus, since the camera control unit 212 can acquire the focal length information of the lens unit 30 via the lens control unit 309, the camera body 20 can be controlled using the focal length information.

  Next, the operation of the camera body 20 of this embodiment will be described. Since the operation of the camera body 20 described with reference to the flowcharts of FIGS. 3 to 6 and FIGS. 11 to 18 in the first embodiment is the same in this embodiment, the description thereof is omitted.

The focus stop threshold value setting of this embodiment executed in S1301 of FIG. 17 will be described using the flowchart of FIG.
In S2601, the camera control unit 212 (focus stop determination unit 213) determines whether or not the focal length of the lens unit 30 is on the wide angle side (smaller value) than the predetermined focal length. If it is on the wide angle side, the process proceeds to S2602. If not, the process proceeds to S2603. The focus stop determination unit 213 sets the focus stop threshold value to X in S2602, and sets the focus stop threshold value to Y in S2603, and ends the process.
The focus stop threshold values X and Y set in the present embodiment have a magnitude relationship of X <Y, as in the focus stop threshold values X and Y in the first embodiment, where Y is 2 or more and X is 1 This is also the same as the example described in the first embodiment.

  In the present embodiment, when the focal length of the lens unit 30 is on the wide angle side from a predetermined value, a small value X is set as the focus stop threshold value. The reason for controlling in this way is that, as the focal length is generally on the wide angle side, the depth of focus is larger and the change in the focus lens position with respect to the change in the focus distance is smaller. That is, generally, as the focal length is on the wide-angle side (smaller), it is less necessary to drive the focus lens with respect to a change in the distance of the subject, and thus the problem with followability becomes smaller. Therefore, when the focal length is wide enough to reduce the number of times the focus lens is driven, the focus stop threshold is set to 1 so that the defocus is within the focal depth and the reliability is better than the predetermined value. As soon as the amount is detected, the focus lens is determined to be in focus and the drive of the focus lens is stopped. If the focal depth or depth of field of the lens unit 30 obtained from the aperture value and the focal length of the lens unit 30 is greater than or equal to a predetermined value, the focusing stop threshold value may be set once.

As described above, in the present embodiment, when the focal length is on the wide-angle side from the predetermined focal length, the focus stop threshold value is set to be smaller than in the case where the focal length is not so that a substantially unnecessary focus lens is obtained. Can be stopped more efficiently. Therefore, the stability of the focus degree can be improved.
Although X is set to 1 and Y is set to 2 or more as the focus stop threshold, other values can be set as long as X <Y as in the first embodiment.

  Although the present invention has been described in detail based on the exemplary embodiments thereof, the present invention is not limited to these specific embodiments, and various modifications can be made within the scope of the invention described in the claims. Modifications can be made.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (11)

Detection means for detecting a defocus amount of the photographing optical system based on an image signal used for focus detection of a phase difference detection method acquired from an image sensor;
Control means for controlling drive of a focus lens included in the photographing optical system;
Determination means for determining whether or not the photographing condition matches a predetermined condition for reducing the detection accuracy of the defocus amount ;
Wherein,
A defocus amount equal to or less than a predetermined amount has been detected a plurality of predetermined second times equal to or less than the first plurality of times by the first plurality of defocus amount detections performed by the detection unit. Control the drive of the focus lens to stop the drive of the focus lens,
If the previous SL photographing condition is determined to meet the above condition, by the first plurality of defocus amount detection is less than the defocus amount of more than the amount that the predetermined said second plurality of times when it is detected a predetermined number of times or more, the focus lens to that imaging device and controls the driving of the focus lens so as to stop the driving of the. The condition, and that the image height of the focus detection area is a predetermined value or more, the image pickup apparatus according to claim 1, characterized in that it comprises at least one of that aperture value is a predetermined value or more . Detection means for detecting a defocus amount of the photographing optical system based on an image signal used for focus detection of a phase difference detection method acquired from an image sensor;
Control means for controlling driving of a focus lens included in the photographing optical system,
The control means detects a predetermined second plurality of defocus amounts less than or equal to a predetermined amount by detecting the defocus amounts for the first predetermined number of times by the detection means. Control the drive of the focus lens to stop the drive of the focus lens when detected more than once,
The focal length of the photographing optical system is variable,
When the focal length is equal to or smaller than a predetermined value, the control means detects a defocus amount equal to or smaller than the predetermined amount by detecting the defocus amount for the first plurality of times. when it is detected smaller predetermined number of times or more than the, the focus lens, wherein the to that imaging device to control the drive of the focus lens so as to stop the driving of the. It said control means by said first plurality of defocus amount detection, in the case where the predetermined amount or less of the defocus amount, is detected in succession said second plurality of times, the driving of the focus lens The imaging apparatus according to any one of claims 1 to 3 , wherein driving of the focus lens is controlled so as to stop the operation. Detection means for detecting the defocus amount of the photographing optical system and the reliability of the defocus amount based on an image signal used for focus detection of the phase difference detection method acquired from the image sensor;
Control means for controlling driving of a focus lens included in the photographing optical system,
The control means is configured to detect a defocus amount whose reliability is better than a predetermined value and equal to or less than a predetermined amount by detecting the defocus amount for the first predetermined number of times by the detecting means. The focus lens drive is controlled so as to stop the drive of the focus lens when a predetermined second multiple times or more is detected. Said control means by said first plurality of defocus amounts detected, the better reliability than the predetermined value, and the defocus amount the at most a predetermined amount, the continuous second plurality of times The imaging apparatus according to claim 5, wherein the driving of the focus lens is controlled so that the driving of the focus lens is stopped when detected.   The imaging apparatus according to claim 1, wherein the control unit performs the control during moving image shooting. A detection step of detecting a defocus amount of the photographing optical system based on an image signal used for focus detection of the phase difference detection method acquired from the image sensor;
A determination step of determining whether or not the shooting condition matches a predetermined condition for reducing the detection accuracy of the defocus amount;
A defocus amount equal to or less than a predetermined amount is detected a plurality of predetermined second times equal to or less than the first plurality of times by detecting the defocus amount for the first predetermined number of times in the detection step. A control step of controlling the drive of the focus lens so as to stop the drive of the focus lens included in the photographing optical system,
In the control step, when it is determined that the shooting condition matches the condition, when a defocus amount equal to or less than the predetermined amount is detected a predetermined number of times less than the second plurality of times, A method for controlling an imaging apparatus, wherein the driving of the focus lens is controlled so as to stop the driving of the focus lens. A detection step of detecting a defocus amount of the photographing optical system based on an image signal used for focus detection of a phase difference detection method acquired from an image sensor;
A defocus amount equal to or less than a predetermined amount is detected a plurality of predetermined second times equal to or less than the first plurality of times by detecting the defocus amount for the first predetermined number of times in the detection step. A control step of controlling the drive of the focus lens so as to stop the drive of the focus lens included in the photographing optical system,
The focal length of the photographing optical system is variable,
In the control step, when the focal distance is equal to or smaller than a predetermined value, the defocus amount equal to or smaller than the predetermined amount is detected in the second plurality of times by the first defocus amount detection. And controlling the focus lens drive so as to stop the drive of the focus lens when a predetermined number of times less than the predetermined number of times is detected. A detection step of detecting a defocus amount of the photographing optical system and reliability of the defocus amount based on an image signal used for focus detection of a phase difference detection method acquired from an image sensor;
A control step of controlling driving of a focus lens included in the photographing optical system,
In the control step, a defocus amount whose reliability is better than a predetermined value and equal to or less than a predetermined amount is detected by the first defocus amount detection performed in advance by the detection step. A control method for an imaging apparatus, wherein the driving of the focus lens is controlled so as to stop the driving of the focus lens when it is detected a plurality of predetermined second or more times. A computer imaging apparatus has a program to function as each unit of the imaging apparatus as claimed in any one of claims 7.

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