JP2019090855A - Imaging device and control method therefor - Google Patents

Abstract

To achieve stable focus tracking when performing focus control during zooming operation.SOLUTION: The present invention includes: a setting step for setting a plurality of focus detection regions; and a selection step for executing a first region selection process of selecting a focus detection region that is the object of focus adjustment on the basis of the result of focus detection in the plurality of focus detection regions and a second region selection process of selecting a focus detection region that is the object of focus adjustment from the focus detection regions, among the plurality of focus detection regions, that conform to a specific condition. In the selection step, the first region selection process is executed when a zoom lens is not moving, and the second region selection process is executed when the zoom lens is moving.SELECTED DRAWING: Figure 12

Description

  The present invention relates to focusing technology in an imaging apparatus having a zoom function.

  2. Description of the Related Art Conventionally, in an imaging apparatus such as an electronic still camera, there is known an imaging apparatus that moves a focusing lens in accordance with the movement of a zoom lens in order to shoot an image in focus on a subject during zoom operation.

  Patent Document 1 proposes a method of focusing during zooming using imaging surface phase difference AF. Further, Patent Document 2 proposes a method of focusing during zooming using contrast detection AF.

Patent No. 6127730 JP, 2013-29628, A

  However, in the prior art disclosed in Patent Documents 1 and 2 described above, there is a possibility that a change in focus unintended by the photographer may occur. Specifically, this is the case of an imaging apparatus provided with a block of a focus detection area composed of a plurality of focus detection areas. In the case of such an imaging device, the photographer roughly designates the position of the block of the focus detection area with respect to the subject to be focused on, and focuses on the focus detection result of the block of the designated focus detection area. I expect that. Therefore, according to the methods of Patent Documents 1 and 2, when the block of the focus detection area is set apart from the position of the block of the designated focus detection area, in particular, near the center of the optical axis, the photographer The focus may change to an unintended position.

  On the other hand, when the block of the focus detection area is disposed out of the vicinity of the optical axis center, it is difficult to keep on capturing the same subject compared to the case where the block is disposed near the optical axis center. Challenges that In particular, in the case of a focus adjustment method where focus detection results are calculated in a short time, such as imaging plane phase difference AF, and in-focus state can be efficiently obtained, each focus detection area is affected by movement of the subject. Detection results may change frequently. When such a focus detection result is used for focus control during zooming, an unexpected change in focus may occur to the photographer, resulting in a moving image with a sense of discomfort.

  Therefore, an object of the present invention is to provide an imaging device that enables stable focus tracking even when zoom operation is performed.

  A technical feature of the present invention is a control method of an imaging apparatus capable of changing a focal length by movement of a zoom lens, which comprises: setting a plurality of focus detection areas; and focus detection results of the plurality of focus detection areas And selecting a focus detection area to be subjected to focus adjustment from among focus detection areas that meet specific conditions among the plurality of focus detection areas. And a second step of selecting a second area, and in the selecting step, if the zoom lens is not moving, the first area selecting process is performed, and the zoom lens is moving. In some cases, the second area selection process is performed.

  According to the present invention, stable focus tracking can be performed even when the zoom operation is performed.

FIG. 1 is a block diagram showing an imaging device of a first embodiment. It is an explanatory view showing a partial field of an image sensor. It is a figure which shows the image signal obtained from the detection area which detects defocusing quantity. It is a figure which shows a correlation amount waveform, a correlation change amount waveform, and a focus shift amount. It is a figure which shows the method of calculating 2 image coincidence. 5 is a flowchart of phase difference AF processing. It is an explanatory view showing a cam locus. 5 is a flowchart showing an AF control process of the first embodiment. 5 is a flowchart showing a target position selection process of the first embodiment. FIG. 8 is an explanatory diagram regarding focus control during zooming in the first embodiment. FIG. 7 is an explanatory diagram of a block of a focus detection area configured by the multipoint focus detection area according to the first embodiment. 5 is a flowchart showing focus detection area selection processing according to the first embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

<Configuration of Imaging Device>
In this embodiment, an example in which the present invention is applied to an imaging apparatus in which a lens barrel and an imaging apparatus are integrated is shown.

  FIG. 1 is a block diagram showing the configuration of the main part of the imaging apparatus.

  As shown in FIG. 1, the imaging device 100 of the lens barrel is configured around a camera control unit 114 that supervises the operations of the lens barrel and the entire imaging device. The control of the imaging apparatus is executed based on a control program stored in a ROM and a RAM (not shown) in the camera control unit 114 and various data necessary for the control.

  First, the configuration of the portion related to the lens barrel will be described. The lens barrel includes a zoom lens 101, an aperture 102, a focus lens 103, a zoom lens drive unit 104, an aperture drive unit 105, and a focus lens drive unit 106.

  The zoom lens 101 is driven by the zoom lens drive unit 104, and the focal length (zoom magnification) can be changed. The diaphragm 102 is driven by the diaphragm driving unit 105, and controls the amount of light incident on the image sensor 107 described later. The focus lens 103 is driven by the focus lens drive unit 106, and adjusts the focus formed on the image sensor 107 described later. The zoom lens drive unit 104, the diaphragm drive unit 105, and the focus lens drive unit 106 are controlled by the camera control unit 114. These determine the position of the zoom lens 101, the aperture amount of the diaphragm 102, and the position of the focus lens 103, and the camera control unit 114 controls the lens from the zoom lens drive unit 104, the diaphragm drive unit 105, and the focus lens drive unit 106. get information.

  Next, the configuration of the part related to the imaging function of acquiring an imaging signal from the light flux that has passed through the imaging optical system will be described. The imaging device 107, the CDS / AGC circuit 108, a camera signal processing unit 109, an AF signal processing unit 110, a display unit 111, a recording unit 112, a camera control unit 114, and a camera operation unit 115 are provided. The image sensor 107 is a member as an image sensor, and is configured of a CCD, a CMOS sensor, or the like. The light flux that has passed through the photographing optical system of the lens barrel is imaged on the light receiving surface of the image sensor 107, and is converted into a signal charge corresponding to the amount of incident light by the photodiode. The signal charge stored in each photodiode is sequentially read out from the imaging element 107 as a voltage signal corresponding to the signal charge based on the drive pulse supplied from the timing generator 113 in accordance with an instruction from the camera control unit 114.

  The video signal and the AF signal read out from the image sensor 107 are input to the CDS / AGC circuit 108 for sampling and gain adjustment, and the video signal is sent to the camera signal processing unit 109 and the signal for imaging plane phase difference AF is The respective signals are output to the AF signal processing unit 110.

  The camera signal processing unit 109 performs various types of image processing on the signal output from the CDS / AGC circuit 108 to generate a video signal.

  A display unit 111 configured by an LCD or the like displays the video signal output from the camera signal processing unit 109 as a captured image.

  The recording unit 112 records the video signal from the camera signal processing unit 109 on a recording medium such as a magnetic tape, an optical disk, or a semiconductor memory.

  The AF signal processing unit 110 performs correlation calculation based on the two image signals for AF output from the CDS / AGC circuit 108, and the defocus amount, reliability information (two-image coincidence, two-image steepness, contrast) Information, saturation information, flaw information etc.) are calculated. The calculated defocus amount and the reliability information are output to the camera control unit 114. Also, the camera control unit 114 notifies the AF signal processing unit 110 of a change in settings for calculating these based on the acquired defocus amount and reliability information. The details of the correlation calculation will be described later with reference to FIGS. 3 to 5.

  The camera control unit 114 performs control by exchanging information with the entire imaging apparatus 100. In addition to the processing in the imaging apparatus 100, the user performs operations such as power on / off, setting change, start of recording, start of AF control, confirmation of recorded video, etc. according to an input from the camera operation unit 115 Perform various camera functions.

<Configuration of Image Sensor>
FIG. 2 shows a part of the light receiving surface of the image sensor 107 as an image sensor. In order to enable imaging surface phase difference AF, the imaging element 107 arranges pixel portions holding two photodiodes as light receiving portions as an optical photoelectric conversion unit in an array. Thus, it is possible to receive the luminous flux obtained by dividing the exit pupil of the lens barrel in each pixel portion.

  FIG. 2A is a schematic view of a part of the image sensor surface of the example of the Bayer arrangement example of red (R), blue (B) and green (Gb, Gr) as a reference. FIG. 2B is an example of a pixel portion in which two photodiodes as photoelectric conversion means are held with respect to one microlens corresponding to the arrangement of the color filters in FIG. 2A.

  The image sensor having such a configuration can output two signals (hereinafter also referred to as an A image signal and a B image signal) for phase difference AF from each pixel unit.

  Also, it is possible to output a signal for recording of imaging (image A signal + image B signal) obtained by adding the signals of two photodiodes. In the case of the added signal, a signal equivalent to the output of the image sensor of the Bayer arrangement example schematically described in FIG. 2A is output. The AF signal processing unit 110 described later performs correlation calculation of two image signals using such an output signal from the image sensor 107 as an image sensor, and calculates information such as defocus amount and various reliability.

  In the present embodiment, a total of three signals of a signal for imaging and two signals for phase difference AF are output from the imaging element 107. This point is not limited to such a method. For example, a total of two signals of one of two signals of a signal for imaging and an image signal for phase difference AF may be output. In this case, the other one of the two signals of the image signal for phase difference AF after output is calculated using the two output signals from the imaging element 107.

  Further, FIG. 2 shows an example in which pixel portions holding two photodiodes as photoelectric conversion means for one microlens are arranged in an array. In this respect, pixel portions holding three or more photodiodes as photoelectric conversion means may be arrayed in an array with respect to one microlens. In addition, a plurality of pixel units in which the opening position of the light receiving unit is different from the microlens may be provided. That is, it is sufficient if two signals for phase difference detection, such as an A image signal and a B image signal, can be obtained as a result.

<Correlation calculation of imaging surface phase difference AF method>
FIG. 3D illustrates an area for acquiring an image signal, and is a conceptual diagram on a pixel array of the imaging element 107 as an image sensor. In contrast to a pixel array 303 in which pixel units (not shown) are arranged in an array, an area to be described below is an area 304. A combination of the shift area 305 necessary for the correlation calculation at the time of calculating the defocus amount of the area 304 and the area 304 is the shift area 306 necessary for performing the correlation calculation.

  In FIGS. 3 and 4, p, q, s, and t represent coordinates in the x-axis direction, p to q represent the shift area 306, and s to t represent the area 304.

  FIGS. 3A, 3B, and 3C are image signals acquired from the shift area 306 set in FIG. 3D. s to t correspond to the area 304, and p to q are image signals corresponding to the shift area 306 in the range necessary for calculation for calculating the defocus amount based on the shift amount. FIG. 3A is a diagram conceptually showing waveforms of the A and B image signals before shift for correlation calculation. The solid line 301 is an A image signal A, and the broken line 302 is a B image signal.

  FIG. 3 (B) is a conceptual diagram in the case of mutually shifting the image waveform before shift in (A) in the positive direction, and FIG. 3 (C) in the negative direction with respect to the image waveform before shift in (A). It is a conceptual diagram at the time of making it mutually shift. When calculating the correlation amount which is the condition of the correlation between the two images, for example, it is possible to shift the A image signal 301 and the B image signal 302 in the direction of the arrows by one bit.

  Subsequently, a method of calculating the correlation amount COR will be described. First, as shown in FIGS. 3B and 3C, for example, the image signal A and the image signal B are shifted one bit at a time, and the absolute value of the difference between the A and B image signals in each state is calculated. Calculate the sum. At this time, the shift amount is represented by i, the minimum shift number is p-s in FIG. 4, and the maximum shift number is q-t in FIG. Also, x is the start coordinate of the focus detection area, and y is the end coordinate of the focus detection area. Using these, it is computable by the following formula (1).

  FIG. 4A is a conceptual diagram showing the correlation amount as a waveform graph. The horizontal axis of the graph indicates the shift amount, and the vertical axis indicates the correlation amount. The correlation amount waveform 401 is an example diagram having extreme values near 402 and 403. Among them, the smaller the correlation amount, the higher the degree of coincidence between the A image and the B image.

Subsequently, a method of calculating the correlation change amount ΔCOR will be described. First, from the conceptual diagram of the correlation amount waveform of FIG. 4A, for example, the correlation change amount is calculated from the difference between the correlation amounts of one shift skipping. At this time, the shift amount is represented by i, the minimum shift number is p−s in FIG. 3 (D), and the maximum shift number is q−t in FIG. 3 (D). Using these, it can calculate by the following formula (2).
ΔCOR [i] = COR [i-1] -COR [i + 1]
{(P−s + 1) <i <(q−t−1)} (2)

  FIG. 4B is a conceptual diagram illustrating the correlation change amount ΔCOR with a waveform graph. The horizontal axis of the graph indicates the shift amount, and the vertical axis indicates the correlation change amount. The correlation variation waveform 404 has points 405 and 406 at which the correlation variation goes from positive to negative. From this point 405, it is the shift amount between the A image signal and the B image signal that the degree of coincidence between the A image and the B image is relatively high when the correlation change amount becomes 0. The shift amount at that time corresponds to the defocus amount.

  FIG. 5A is an enlarged view of the point 405 in FIG. 4B, and the waveform of a part of the waveform 404 of the correlation change amount is a waveform 501. A method of calculating the defocus amount PRD corresponding to the defocus amount will be illustrated using FIG. 5 (A). The focus deviation amount is divided into an integer part β and a decimal part α for conception. The fractional part α can be calculated by the following equation (3) from the similarity relationship between the triangle ABC and the triangle ADE in the figure.

Subsequently, the fractional part β can be calculated by the following equation (4) from FIG. 5 (A).
β = k−1 (4)

  As described above, the defocus amount PRD can be calculated from the sum of α and β.

When there are a plurality of zero crossings as shown in FIG. 4B, the place where the steepness maxder (hereinafter referred to as the steepness) of the correlation amount change at the zero crossings is large is taken as a first zero crossing. The steepness is an index indicating the ease of AF, and indicates that the larger the value, the easier the point is to perform AF. The steepness can be calculated by the following equation (5).
maxder = │ΔCOR [k-1] │ + │ΔCOR [k] │ (5)

  As described above, when there are a plurality of zero crossings, the first zero crossing is determined by the steepness.

Subsequently, a method of calculating the reliability level of the focus shift amount will be illustrated. This corresponds to the reliability of the defocus amount, but the description given below may be used to calculate the reliability level by another known method by way of example. The reliability can be defined by the above-described sharpness and the degree of coincidence fnclvl (hereinafter referred to as the degree of coincidence of two images) of the two images of the A and B image signals. The degree of image coincidence is an index that represents the accuracy of the amount of focus shift, and the smaller the value, the better the accuracy. FIG. 5B is an enlarged view of a portion near the extreme value 402 in FIG. 4A, which is a waveform 502 which is a waveform of a part of the correlation amount waveform 401. From this, the steepness and the degree of coincidence between two images are illustrated for the calculation method. The degree of image coincidence can be calculated by the following equation (6).
(I) When | ΔCOR [k−1] | × 2 ≦ maxder
fnclvl = COR [k-1] + ΔCOR [k-1] / 4
(Ii) when | ΔCOR [k−1] | × 2> maxder
fnclvl = COR [k] -ΔCOR [k] / 4 (6)

<Calculating defocus amount>
FIG. 6 shows the flow of a series of processing up to calculation of the defocus amount. In the following description of the example, the defocus amount and the defocus amount are distinguished and illustrated. In this respect, the defocus amount in the technical concept of the present application may be conceptualized as an absolute distance from the in-focus position or the number of pulses, or may be a conceptual or relative concept different from such concept, dimension or unit. It is a concept indicating how much it can be determined that the subject is out of focus and how much focus control can be made to make it possible to shift to the in-focus state. Acquisition of defocus information as such a concept is described as "acquisition of focus information".

  In step S601, the image signals A and B are acquired from the pixel at the position of the imaging element 107 corresponding to each of the areas set as illustrated above. Next, the amount of correlation is calculated from the acquired image signal (step S602). Subsequently, the correlation change amount is calculated from the calculated correlation amount (step S603). Then, the focus shift amount is calculated from the calculated correlation change amount (step S604). Further, a reliability level indicating how much the calculated defocus amount can be trusted is calculated (step S605). A number of these processes is performed according to the number of focus detection areas. Then, the defocus amount is converted into the defocus amount for each focus detection area (step S606).

<Reliability level of defocus amount>
Next, the reliability level of the defocus amount in the present embodiment will be described.

  The reliability level of the defocus amount is an index indicating the accuracy of the calculated defocus amount, and is calculated by the AF signal processing unit 110 in FIG. Basically, the reliability level is high when it can be judged that the defocus amount calculated is reliable, and the reliability level is lowered as it becomes unreliable. The reliability level in the present embodiment is expressed by numerical values from 1 to 4, 1 being the highest reliability and 4 being the lowest reliability. The detail of each reliability is as follows.

  The contrast between the A image signal and the B image signal is high, and the shapes of the A image signal and the B image signal are similar to those in the case where the reliability level of the defocus amount is “1” (two image coincidence level is high) This is the case where the camera is in a state or in a state in which the image of the main subject is already in focus. In this case, the drive is performed by relying on the defocus amount.

  When the reliability level of the defocus amount is “2”, the contrast of the A image signal and the B image signal is high but the shapes of the A image signal and the B image signal are similar although the reliability level is not as low as “1”. Show the status. Alternatively, it shows a state in which the main subject image is already in the vicinity of the in-focus position within a certain error range. In this case, the target position is determined and driven based on the defocus amount.

  When the reliability level of the defocus amount is "3", although the two-image coincidence degree level calculated by the AF signal processing unit 110 is lower than a predetermined value, the A and B image signals are relatively shifted. There is a fixed tendency in the correlation obtained by the above, and the defocus direction is in a reliable state. For example, the determination is often performed in a state in which the main subject is slightly blurred.

  When the defocus amount and the defocus direction are not reliable either, it is determined that the reliability level is “4”. For example, the contrast of the A image signal and the B image signal is low, and the image matching level is also low. This is often the case where the object is largely blurred, and it is difficult to calculate the defocus amount.

<Block of focus detection area>
Next, the blocks of the focus detection area configured by the multi-point focus detection area in the present embodiment will be described.

  The block in the focus detection area is the area to be calculated in FIG. 3D arranged in a grid, and as shown in FIGS. 11A and 11B, the focus detection of 3 × 3 points in this embodiment is performed. Set the area. The image sensor 107 as an image sensor in the present embodiment described above with reference to FIG. 2 can output two signals for phase difference AF from each pixel unit, and the focus detection area is set at an arbitrary position. It is possible. Therefore, as shown in FIG. 11 (a), it is possible to move one arranged in a lattice at the center of the optical axis to the position shown in FIG. 11 (b) according to an input from the camera operation unit 115 and set it.

  In this embodiment, the defocus amount is calculated from each focus detection area of the block of the focus detection area, and focus adjustment is performed based on the result.

<AF control processing>
Next, AF control processing performed by the camera control unit 114 will be described using FIG.

  FIG. 8 is a flowchart showing the AF control process performed by the camera control unit 114 in FIG. This process is executed according to a computer program stored on the ROM in the camera control unit 114. For example, it is executed at a reading cycle (for each vertical synchronization period) of an imaging signal from the imaging element 107 for generating one field image (hereinafter, also referred to as one frame or one screen). In addition, it may be repeated every plural vertical synchronization periods (V rates).

  First, in step S801 in FIG. 8, the AF signal processing unit 110 confirms whether the AF signal has been updated. At this time, when the AF signal is updated, the result (the defocus amount and the reliability) is acquired in the next step S802. On the other hand, when the AF signal is not updated at step S801, the process is ended as it is.

  Next, in step S803, it is determined whether the zoom lens 101 is moving. Specifically, when the photographer operates the zoom operation lever or the like in the camera operation unit 115, the camera control unit 114 that detects it controls the zoom lens drive unit 104 to drive the zoom lens 101 at a predetermined speed. Do. Thus, the camera control unit 114 recognizes the movement state of the zoom lens 101. When the zoom lens 101 is not moving at step S803, the process proceeds to the focus detection area selection processing at zoom stop at step S804, and when the zoom lens 101 is moving at step S803, the zoom is performed at next step S809. The process proceeds to focus detection area selection processing. The processes in steps S804 and S809 are both processes for selecting a focus detection area to be subjected to focus adjustment, which is used when determining the target position when moving the focus lens 103 at the current control timing, and the details will be described later. Do.

  If the zoom lens 101 is not moving at step S803, the process proceeds to step S805 after step S804. Step S805 is processing for selecting a target position at the time of zoom stop, which is processing for selecting a target position when moving the focus lens 103, and the details will be described later. Next, in step S806, it is determined whether the in-focus state is achieved. Specifically, as a result of steps S804 and S805, it is determined whether the defocus amount in the selected focus detection area is within a predetermined range. In this embodiment, the focusing state is determined based on whether or not it falls within a range of ± 1 · F · δ with reference to the depth of focus F · δ (F: F value, δ: allowable confusion circle diameter) as a predetermined range. Determine. If it is determined in step S806 that the image is in focus, the process proceeds to step S807, and the focus detection area information (focusing frame information) selected in step S804 is stored. On the other hand, if it is not determined in step S806 that the image is in focus, the process proceeds to step S808 to clear focus detection area information (focusing frame information) selected in the past. Thereafter, in step S812, the camera control unit 114 controls the focus lens drive unit 106 to move the focus lens 103 with respect to the selected and determined target position.

  If the zoom lens 101 is moving at step S803, the process proceeds to step S810 after step S809. Step S810 is processing for selecting a zoom target position, which is processing for selecting a target position when moving the focus lens 103, the details of which will be described later.

  In step S811, the focus lens position at the next control timing is predicted based on the target distance selected in step S810. Specifically, as shown by the cam locus at each object distance in FIG. 7, in order to maintain the in-focus state at a certain object distance, the cam locus of the object distance matching the change of the focal distance is traced It is necessary to control the focus lens. Therefore, in step S811, in order to maintain a state in which the target position selected in step S810 is in focus, it is determined based on the cam locus at which position the focus lens should be controlled at the next control timing. In the present embodiment, it is assumed that the AF control process is executed every vertical synchronization period, so the focal length of the zoom lens 101 advanced by an amount suitable for that time is calculated, and based on that, the focus lens position is calculated from the cam locus. Identify. Further, the cam locus information in this embodiment is stored in the ROM in the camera control unit 114, and the cam locus of the object distance not held on the ROM is obtained by interpolation from the adjacent cam locus.

  Next, in step S812, the camera control unit 114 controls the focus lens drive unit 106 to move the focus lens 103 to the selected and determined target position.

<Selection process of focus detection area at zoom stop>
Next, the zoom stop time focus detection area selection process shown in step S804 in FIG. 8 described above will be described using FIG.

  FIG. 12A is a flowchart illustrating the zoom stop time focus detection area selection process performed by the camera control unit 114 in FIG. As in the case of the AF control process described above, the computer program is executed according to a computer program stored on the ROM in the camera control unit 114.

  First, in step S1201a of FIG. 12A, selection frame information is initialized as preparation in advance. In the zoom stop focus detection area selection process of this embodiment, the focus detection area for determining the defocus amount and the reliability to be used in the zoom stop target position selection process described later is selected from the blocks of the focus detection area. Do. At this time, in step S1201a, a temporary storage area used in the process of selecting a focus detection area that meets the conditions is initialized. The initial selection frame information at this point of time is set as a 3 × 3 center frame.

  Next, in step S1202a, a focus detection area to be evaluated in the subsequent processing is determined. In this embodiment, each focus detection area constituting the block of the focus detection area shown in FIGS. 11a and 11b is processed as an evaluation object frame in the order of (1) to (9).

  Next, in step S1203a, it is determined whether the evaluation of all the focus detection areas constituting the block of the focus detection area has been completed. If the evaluation of all the focus detection areas is completed in step S1203a, the process ends. On the other hand, if the evaluation of all the focus detection areas has not been completed, the process proceeds to the next step S1204a.

  In step S1204a, the degree of reliability generated from the focus detection area to be evaluated is determined. In the present embodiment, if the reliability is higher than 4 in step S1203a, the process proceeds to the next step S1204a, and if smaller, the process returns to step S1202a to process the next focus detection area for evaluation.

  In step S1205a, it is determined whether the evaluation object frame is higher than the reliability of the current selection frame. If it is determined in step S1205a that the evaluation object frame is higher than the reliability of the current selection frame, the process proceeds to step S1206a. If the evaluation object frame is lower, the process returns to step S1202a to process the next evaluation object focus detection area.

  In step S1206a, the detection position calculated based on the defocus amount of the evaluation target frame and the current focus lens position is compared with the detection position of the current selection frame, and the detection position of the evaluation target frame is from the current detection position of the selection frame. Determine if it is also close. If it is determined in step S1206a that the detection position of the evaluation target frame is closer, the process proceeds to step S1207a. If not, the process returns to step S1202a to process the next focus detection area for evaluation.

  In step S1207a, the processing from step S1202a to step S1206a is performed to select and store the focus detection area having the higher reliability and the closest result among the focus detection areas evaluated up to that point. After that, the process returns to step S1202a and proceeds to the processing of the next focus detection area to be evaluated.

  As described above, in the zoom stop time focal point detection area selection process, the focal point detection areas having higher reliability and indicating the near side result are selected from the respective focal point detection areas constituting the blocks of the focal point detection area.

<Selection process of target position at zoom stop>
Next, the zoom-stop target position selection process shown in step S805 in FIG. 8 will be described with reference to FIGS. 9 (A) and 10 (A).

  FIG. 9A is a flowchart showing a zoom stop target position selection process performed by the camera control unit 114 in FIG. Similar to the AF control process described above, the process is executed according to a computer program stored on the ROM in the camera control unit 114.

  First, in step S901a of FIG. 9A, it is determined whether the acquired reliability is “1” based on the reliability of the focus detection area selected in step S804 of FIG. If the degree of reliability is "1" at step S901a, the process proceeds to step S906a. If the degree of reliability is not "1", the process proceeds to step S902a.

  In the case where the reliability is “1”, that is, the accuracy of the defocus amount detected as described above is high, and focusing can be performed by controlling the focus lens to the target position calculated from the defocus amount. is there. Therefore, in step S906a, the focus lens position (detection position) calculated based on the detected defocus amount and the current focus lens position is set as the target position. Thus, how to move the focus lens 103 directly to the detection position is referred to as target drive in this embodiment.

  Thereafter, in step S910a, the search flag is set to OFF, and the process ends. In this embodiment, a target position to be described later is set at the infinite end or the near end of the movable range of the focus lens 103, and the movement for specifying the in-focus position while moving the focus lens 103 is called search drive. The indicated flag is called a search flag.

  Next, in step S 902 a, it is determined whether the acquired reliability is “2”. If the degree of reliability is "2" in step S902a, the process proceeds to step S907a. If the degree of reliability is not "2", the process proceeds to step S903a.

  When the reliability is "2", it means that the accuracy of the defocus amount detected as described above includes a constant error. Therefore, in step S 907 a, the target position is set by multiplying the detected position calculated based on the detected defocus amount and the current focus lens position by the coefficient γ. The coefficient γ is a numerical value less than 1, and γ assumed in this embodiment is 0.8. Therefore, step S 907 a sets the position of 80% of the detected position as the target position. Thus, how to move the focus lens 103 so as to be insufficient at the detection position is called defocus drive in this embodiment.

  Thereafter, in step S910a, the search flag is set to OFF, and the process ends.

  Next, in step S903a, it is determined whether the acquired reliability is "3". If the degree of reliability is "3" in step S903a, the process proceeds to step S908a. If the degree of reliability is not "3", the process proceeds to step S904a.

  In the case where the reliability is "3", that is, although the accuracy of the defocus amount itself detected as described above is low, the defocus direction indicates a reliable state. Therefore, in step S908a, the end of the detected defocus direction is set as the target position, and search drive is performed. Then, in the next step S911a, the search flag is set to ON, and the process ends.

  In step S904a, it is determined whether the search flag is OFF. If the search flag is OFF in step S904a, the process advances to step S909a. If the search flag is ON, the process advances to step S905a.

  The case where the reliability is not "3" in step S903a means that the reliability is "4", and the defocus amount and the defocus direction can not be relied upon. In this case, it is difficult to specify the in-focus position only with the information obtained from the AF signal processing unit 110. Therefore, in step S909a, the end on the wide side of the drive range is set as the target position based on the positional relationship between the current focus lens position and the infinity end and the close end of the focus lens 103, and search drive is performed.

  Then, in the next step S911a, the search flag is set to ON, and the process ends.

  In step S905a, it is determined whether the focus lens 103 has reached either the infinite end or the near end. If one of the ends is reached in step S905a, the process advances to step S909a to reset the target position again. As described above, in order to set the end on the wide side of the drive range as the target position, when the end is reached, the target position is set on the opposite end. On the other hand, if the end has not been reached in step S 905 a, the process ends and the search drive is continued.

  As described above, in the zoom-stop target position selection process in the present embodiment, as shown in the table of FIG. 10A, when the reliability of the defocus amount is high, the target position is set based on the defocus amount. Then, if the degree of reliability is low, the target position is set at the end of the movable range of the focus lens 103. Therefore, as the movement of the entire AF, as the reliability is lower, the movement is performed to specify the in-focus position with a large change in focus.

<Selection process of focus detection area at zoom>
Next, the zoom focus detection area selection process shown in step S809 in FIG. 8 will be described with reference to FIG.

  FIG. 12B is a flowchart showing a zoom focus detection area selection process performed by the camera control unit 114 in FIG. As in the case of the AF control process described above, the computer program is executed according to a computer program stored on the ROM in the camera control unit 114.

  First, in step S1201b of FIG. 12B, it is determined whether it is the first execution. If it is the first time in step S1201b, the process proceeds to step 1202b, and if it is not the first time, the process proceeds to step S1206b.

  In step S1202b, it is determined whether the in-focus frame recorded in step S807 in FIG. 8 exists. If the in-focus frame is present at step S1202b, the process proceeds to the next step S1203b, and if not, the process proceeds to step S1210b.

In step S1203b, the selection frame is set as the in-focus frame. That is, when the in-focus frame exists before the zoom start, the initial selection frame at the zoom uses the in-focus frame immediately before the zoom start.
Next, in step S 1204 b, using the defocus amount of the selected frame and the detection position calculated from the current focus lens position and the current focal length, the subject distance is calculated based on the current focus detection result.

  Next, in step S1205b, the subject distance of the in-focus frame calculated in step S1204b is recorded, and the process is ended. In the series of processes from step S1201b to step S1205b, the in-focus frame before the start of zooming is set as the selection frame during zooming, and the subject distance calculated from the focus detection result of the selection frame is used as the determination criterion for entering and leaving the object in the selection frame. Remember.

  If there is no in-focus frame in step S1202b, the process advances to step S1210b to set the selection frame in the center frame of the 3 × 3 focus detection area block, and the processing ends.

  If it is determined in step S1201b that the process is performed after the first process, the process advances to step S1206b.

  If it is determined in step S1206b that the selection frame is the in-focus frame (if step S1203b is performed), the process advances to step S1207b. If the selection frame is not the in-focus frame, the process advances to step S1210b.

  In step S1207b, the subject distance is calculated based on the focus detection result of the current selection frame, as in step S1204b.

  In step S1208b, the subject distance calculated in step S1207b is compared with the subject distance stored in step S1205b at the start of zooming to determine whether a predetermined distance change has occurred. Note that the predetermined distance change in the present embodiment means a subject distance change equivalent to ± 3 · F · δ with reference to the focal depth F · δ (F: F value, δ: permissible circle of confusion diameter) at the current focal length. Point to If a change in the subject distance to follow is detected in S1208b, the process proceeds to step S1209b, and if a change in the subject distance is not detected, the process proceeds to S1211b.

  When a change in the subject distance is detected, in step S1209b, the in-focus frame is cleared as in step S808 in FIG. 8, and the process proceeds to step S1210b to switch the selection frame.

  In step S1210b, the selection frame is set to the center frame of the block of the 3 × 3 focus detection area, and the process ends.

  If the change in subject distance to follow in step S1208b is not detected, the process advances to step S1211b, and it is determined in step S1211b whether the subject distance to follow in the focusable range at the current focal distance is included. . In this embodiment, it is assumed that the optical system is configured such that the focusable range (focusable distance range) changes between the wide angle side and the telephoto side. In the case of such a configuration, for example, it is assumed that the subject distance focused when starting the zoom operation is out of the focusable range at the focal distance at that point in the process of zooming. Assuming such a case, it is determined in step S1211b whether or not the subject distance to be followed is within the focusable range, and if it is within the range, the processing is ended as it is, and if it is out of the range, the step is Go to S1209 b. The processes after step S1209b are the same as those described above.

  As described above, in the zoom-time focus detection area selection process in this embodiment, the center frame of the block of the focus detection area is used as the selection frame in many cases during zooming. Thus, it is possible to suppress the influence of the in / out of the subject in each focus detection area on the focus control during zooming. In addition, when focusing is performed in any focus detection area of the block of the focus detection area when the zoom is stopped, the focus detection area during zooming is selected taking over the focus detection area. This makes it possible to suppress a large change in focus immediately after the start of zooming. Furthermore, when the in-focus frame is taken over as the selection frame, the change in the subject distance calculated based on the focus detection result of the selection frame used during zooming is monitored to detect the change of the subject in the selection frame. Is possible. Thus, when it is detected that the subject in the selection frame at the start of zooming has moved out of the focus detection area by zooming, the central frame of the block in the focus detection area is switched to the selection frame. For this reason, it is possible to continue the focus control during zooming in a manner that reflects the position of the block in the focus detection area designated by the photographer.

<Selection process of target position at zoom>
Next, the zoom target position selection process shown in step S 808 in FIG. 8 will be described with reference to FIGS. 9B and 10C.

  FIG. 9B is a flowchart showing a zoom target position selection process performed by the camera control unit 114 in FIG. Similar to the AF control process described above, the process is executed according to a computer program stored on the ROM in the camera control unit 114.

  First, in step S 901 b of FIG. 9B, it is determined whether the acquired reliability is “1” based on the reliability of the focus detection area selected in step S 809 of FIG. 8. If the degree of reliability is “1” in step S901 b, the process proceeds to step S904 b. If the degree of reliability is not “1”, the process proceeds to step S902 b.

  In the case where the reliability is “1”, that is, the accuracy of the defocus amount detected as described above is high, and focusing can be performed by controlling the focus lens to the target position calculated from the defocus amount. is there. Therefore, in step S904b, the focus lens position (detection position) calculated based on the detected defocus amount and the current focus lens position is set as the target position.

  Next, in step S902b, it is determined whether the acquired reliability is "2". If the degree of reliability is "2" in step S902b, the process proceeds to step S905b. If the degree of reliability is not "2", the process proceeds to step S903b.

  When the reliability is "2", it means that the accuracy of the defocus amount detected as described above includes a constant error. Therefore, in step S905b, the target position is set by multiplying the detected position calculated based on the detected defocus amount and the current focus lens position by the coefficient α. The coefficient α is a numerical value less than 1 and α assumed in this embodiment is 0.8. Therefore, step S 905 b sets the position of 80% of the detected position as the target position.

  Next, in step S 903 b, it is determined whether the acquired reliability is “3”. If the degree of reliability is "3" in step S903b, the process proceeds to step S906b, and if the degree of reliability is not "3", the process proceeds to step S907b.

  In the case where the reliability is "3", that is, although the accuracy of the defocus amount itself detected as described above is low, the defocus direction indicates a reliable state. Therefore, in step S906b, based on the defocus direction and the current focus lens position, a position shifted from the current position by the shift amount β in the defocus direction is set as the target position. Note that β assumed in the present embodiment is set to about 1 · F · δ based on the focal depth F · δ (F: F value, δ: diameter of permissible circle of confusion).

  If it is determined in step S903b that the reliability is not "3", that is, if the reliability is "4", the process advances to step S907b to set the target position to the current focus lens position.

  After the target position is selected via steps S904b, S905b, S906b, and S907b, the process proceeds to step S908b.

  In step S908b, an actual lens drive amount (actual drive amount in the figure) is calculated from the target position determined in steps S903b to S907b described above and the current focus lens position. It is determined whether it is larger than F · δ. In step S 908 b, the actual driving amount is N. If larger than F · δ, the process proceeds to step S 909 b and the actual driving amount is N.V. In the case of F · δ or less, the processing ends.

  In step S909 b, the actual drive amount is N.V. The target position is set to the current position + N.N so as not to exceed F · δ. Change to F · δ. As described above, when a focus change larger than the predetermined lens drive amount (N · F · δ) occurs regardless of the reliability of the defocus amount by the steps S908 b and S 909 b, the predetermined lens drive amount is settled. Correct the target position. Here, a predetermined lens driving amount N.V. With respect to F · δ, the coefficient N in this embodiment is set to 5, and if there is a possibility that 5 · F · δ, ie, a focus change of about 5 depths or more may occur, the target position is corrected to suppress the focus change.

  As described above, in the zoom target position selection process in the present embodiment, as shown in the table of FIG. 10B, when the reliability of the defocus amount is high, the target position is set based on the defocus amount, and the reliability If is low, the target position is set based on the current lens position. FIG. 10C shows the positional relationship between the current time t1 and the next control timing t2 when the target position is selected by the zoom target position selection process and a series of AF control processes are performed.

  ● at time t1 indicates the current lens position, which matches the distance A. The target position in the case of the reliability levels 1 to 4 of FIG. 10B corresponds to (1) to (4) at time t1 of FIG. That is, in the case of the reliability "1", the distance B, in the case of the reliability "2", the distance C, in the case of the reliability "3", the distance D, and in the case of the reliability "4", the same distance A as the current position. is there. Further, as shown in step S 908 b and step S 909 b in FIG. 9B, when the target position is larger than the predetermined lens driving amount (N · F · δ), the distance E is satisfied at (5) at time t1. . In this case, the zoom stop target position selection process is corrected to the distance F of (6).

  In the zoom target position selection process, target positions (1) to (4) and (6) at the current time t1 are selected and determined in accordance with the reliability of the defocus amount. Then, in step S810 in FIG. 8, each lens position at time t2 of the next control timing is calculated from the cam locus, and in step S811 the focus lens is driven toward the target position at time t2.

  According to this embodiment, during the zoom operation, the focus detection area to be followed is selected based on the selection rule of the focus detection area different from the case where the zoom operation is not performed, and the focus lens is controlled based on the focus detection result. This enables stable focus tracking.

(Other embodiments)
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. Can also be realized. It can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

  Moreover, in each embodiment mentioned above, although the case where this invention was applied to a digital camera was made into an example and demonstrated, this is not limited to this example. That is, the present invention may be applied to any device associated with an imaging device. That is, the present invention is applicable to any device capable of capturing an image, such as a mobile phone terminal, a portable image viewer, a television equipped with a camera, a digital photo frame, a music player, a game machine, and an electronic book reader.

  Further, in the above-described embodiment, the imaging apparatus in which the lens barrel and the imaging apparatus are integrated is described. However, the imaging apparatus may be an interchangeable lens type. The interchangeable lens type imaging device is configured to include an interchangeable lens unit (lens barrel) and a camera body (imaging device). A lens control unit that generally controls the operation of the entire lens unit and a camera control unit that generally controls the operation of the camera system including the lens unit are configured to be able to communicate with each other through terminals provided on the lens mount.

DESCRIPTION OF SYMBOLS 100 Imaging device 101 Zoom lens 103 Focus lens 104 Zoom lens drive part 106 Focus lens drive part 107 Image sensor 110 AF signal processing part 111 Display part 112 Recording part 114 Camera control part 115 Camera operation part

Claims (9)

An imaging apparatus capable of changing a focal length by movement of a zoom lens,
Setting means for setting a plurality of focus detection areas;
A first area selection process for selecting a focus detection area to be adjusted based on the focus detection results of the plurality of focus detection areas, and a focus detection area that meets a specific condition among the plurality of focus detection areas And selecting means for performing a second area selection process of selecting a focus detection area to be subjected to focus adjustment.
The selection unit performs the first area selection process when the zoom lens is not moving, and performs the second area selection process when the zoom lens is moving. Imaging device.   The image pickup apparatus according to claim 1, wherein the plurality of focus detection areas are configured by a plurality of grid-like focus detection areas.   The image pickup apparatus according to claim 1, wherein the first area selection process selects a focus detection area of a closest focus detection result.   The focus detection area meeting the specific condition in the second area selection process is a focus detection area located at the center of the plurality of focus detection areas, and the specific area is satisfied in the second area selection process. The imaging apparatus according to any one of claims 1 to 3, wherein the focus detection area is continuously selected.   A focus detection area that meets the specific condition in the second area selection process when the zoom lens starts moving is a focus that has been selected by the first area selection process and focused by focus adjustment. The imaging device according to any one of claims 1 to 3, which is a detection area. It further comprises detection means for detecting changes in subject distance,
When there is no change in the subject distance of the focus detection area selected when the zoom lens starts moving, the focus detection area meeting the specific condition in the second area selection process while the zoom lens is moving The focus detection area is the selected focus detection area, and when there is a change in the subject distance, the focus detection area is located at the center of the plurality of focus detection areas. The imaging device according to.   When the zoom lens starts moving, if focusing is not achieved in the focus detection area selected by the first area selection processing, the focus detection areas of the plurality of focus detection areas are selected in the second area selection processing. 7. The image pickup apparatus according to claim 5, wherein a focus detection area located at the center is selected, and the zoom lens is continuously selected even during movement.   In the case where the focus detection area is selected by taking over the result of the first area selection processing in the second area selection processing, the subject distance exceeds the focusable range at the focal length at that time. In the second area selection process, the focus detection area located at the center of the plurality of focus detection areas is selected, and the selection is continuously continued even while the zoom lens is moving. The imaging device according to. It is a control method of an imaging apparatus in which a focal length can be changed by movement of a zoom lens,
Setting steps of setting a plurality of focus detection areas;
A first area selection process for selecting a focus detection area to be adjusted based on the focus detection results of the plurality of focus detection areas, and a focus detection area that meets a specific condition among the plurality of focus detection areas And a second step of selecting a focus detection area to be subjected to focus adjustment.
In the selection step, the first area selection process is performed when the zoom lens is not moving, and the second area selection process is performed when the zoom lens is moving. Control method.

Images