JP2015152749A - Imaging device and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device that enables reduction of a fall in definition quality of a photographing image due to a change in magnification without taking time for a focus detection.SOLUTION: A photographing optical system including a focus lens performing a focus adjustment by a movement comprises: first focus detection means that is configured to perform a focus detection by a contrast AF having a wobbling mode causing the focus lens to move toward an in-focus direction to detect an in-focus position; second focus detection means that is configured to perform the focus detection by a focus detection pixel discretely arranged in an image pickup element. When a change in magnification of the photographing optical system due to the wobbling action of the first focus detection means is smaller than a prescribed range, a focus detection is performed by the first focus detection means, and when the change in magnification of the photographing optical system due to the wobbling action of the first focus detection means is larger than the prescribed range, the focus detection is performed by the second focus detection means.

Description

  The present invention relates to an image pickup apparatus that picks up an image of a subject, and more particularly to an image pickup apparatus capable of hybrid AF of a phase difference detection method and a contrast detection method in an image pickup element.

  Regarding an imaging apparatus capable of hybrid AF of focus control by a contrast detection method (hereinafter referred to as a first AF method) and focus control by a phase difference detection method (hereinafter referred to as a second AF method) in an image sensor. A technique as disclosed in Patent Document 1 is proposed. According to the contents disclosed in Patent Document 1, since the pupil of the focus detection pixel for performing the second AF method is focused by narrowing the aperture of the photographing lens, it is difficult to perform normal focus detection. It is described that when the lens is mounted and the photographing lens is narrowed down, focusing accuracy is improved by performing a focus detection operation by wobbling using the first AF method.

  Further, a technique as disclosed in Patent Document 2 has been proposed regarding control when a wobbling operation is performed. In Patent Document 2, as a method for preventing deterioration in the quality of a photographed image due to the magnification fluctuation caused by the focus detection operation by wobbling using the first AF method, the magnification fluctuation in the required wobbling width is large, and the quality of the photographed image is high. A method for improving the quality of a captured image by limiting the wobbling width and increasing the number of samplings is disclosed.

JP2012-118154A JP 2008-170508 A

  However, in the prior art disclosed in Patent Document 1 described above, by narrowing down the aperture, the depth of field becomes deeper and the contrast difference becomes difficult to occur, so that it is difficult to detect contrast in a narrow wobbling range. There is a possibility that the wobbling width necessary for the detection may deteriorate the quality of the photographed image due to the magnification fluctuation accompanying the wobbling operation during moving image photographing. In addition, with the technique disclosed in Patent Document 2, it is possible to improve the deterioration of the quality of the captured image due to the magnification variation, but it takes time to detect the focus.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an imaging apparatus that can reduce deterioration in quality of a captured image due to magnification fluctuations without taking time for focus detection.

  In order to achieve the above object, according to the present invention, in an imaging apparatus that forms an image of a subject on an imaging element by the imaging optical system to generate an image representing the subject, the imaging optical system performs focus adjustment by movement. It includes a focus lens, detects the focus position by detecting the contrast of the image obtained by the image sensor while moving the focus lens, and performs the wobbling operation to recognize the focus direction. However, the first focus detecting means by contrast AF having a wobbling mode for detecting the in-focus position by moving the focus lens in the in-focus direction, and the second by the focus detection pixels discretely arranged on the image sensor. When the magnification fluctuation of the photographing optical system is smaller than a predetermined range due to the wobbling operation of the first focus detection means. , The focus detection by the first focus detection unit, wherein when the change in magnification of the photographing optical system is greater than the predetermined range, and performs the focus detection by the second focus detection unit.

  Further, the magnification variation amount accompanying the wobbling operation is calculated from the aperture and magnification variation information of the photographing optical system.

  Further, the focus detection accuracy by the second focus detection unit is determined, and when the second focus detection method accuracy is equal to or higher than a predetermined value, the focus detection by the second focus detection unit is performed with an accuracy of a predetermined value or less. In this case, the focus detection by the first focus detection means is performed.

  Further, the focus detection accuracy by the second focus detection unit is determined, and when the second focus detection method accuracy is equal to or higher than a predetermined value, the focus detection by the second focus detection unit is performed with an accuracy of a predetermined value or less. In such a case, a warning is displayed.

  According to the present invention, in an imaging apparatus capable of hybrid AF of a phase difference detection method and a contrast detection method with an image sensor, the quality of a captured image is improved by using the first AF method and the second AF method separately. An imaging device capable of reducing the decrease can be provided.

  Further, it is possible to calculate in advance the magnification fluctuation associated with the wobbling operation from the aperture and magnification fluctuation information of the photographing optical system.

  Further, when the second AF method accuracy is NG, priority is given to focusing, and focus detection can be performed by the first AF method.

  When the second AF method accuracy is NG, it is possible to make the user recognize by giving a warning to the user.

Schematic which shows the structure of the imaging device based on embodiment of this invention Schematic which shows the structure of the imaging device at the time of live view based on embodiment of this invention The block diagram which shows the electrical constitution of the imaging device based on embodiment of this invention The figure which shows an example of the pixel arrangement | sequence of an image pick-up element group and a focus detection pixel group Schematic diagram for explaining image phase shift due to focus shift Flowchart of focus detection according to an embodiment of the present invention The figure which shows an example of the magnification fluctuation by the focus of a taking lens

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

[Example 1]
1 and 2 are schematic diagrams showing the configuration of an imaging apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 100 denotes an imaging apparatus main body. Reference numeral 101 denotes a CPU which controls the imaging apparatus 100. Reference numeral 102 denotes an interchangeable photographic lens body, which has a focus lens 103 that moves in the optical axis direction during focus adjustment, a zoom lens (not shown) that moves in the optical axis direction during zooming, lens information such as a diaphragm 104 and a lens ID. And a lens CPU 105 that controls the focus lens 103 and the diaphragm 104 based on a command from the CPU 101 of the imaging apparatus 100. Reference numeral 106 denotes an imaging element made of CMOS (Complementary Metal Oxide Semiconductor), and has an imaging pixel group 107a made up of pixels used for acquiring image signals for imaging, with RGB color filters provided on the light receiving surface.

  Further, the image sensor 106 is a pair of phase difference sensors whose optical configurations are used for focus detection and whose optical axes are targets, and includes a plurality of sets of phase difference sensors and a focus detection pixel group existing in a plurality of focus detection areas. 107b. Reference numeral 109 denotes a main mirror, which is configured as a semi-transmissive mirror. Reference numeral 112 denotes a focusing screen, which is disposed on an imaging plane equivalent to the imaging plane of the image sensor 106 on which the subject image transmitted through the photographing lens 102 is formed. Reference numeral 117 denotes a subject optical path, and the light beam that has passed through the photographing lens 102 is reflected by the main mirror 109 and is primarily imaged on the focusing screen 112.

  The pentaprism 113 changes the subject optical path 117 and corrects the subject image formed on the focusing screen 112 to an erect image. The eyepiece 114 allows the photographer 115 to observe the subject image formed on the focusing screen 112. Reference numeral 110 denotes a sub mirror, and the subject light flux that has passed through the main mirror 109, which is a half mirror, is guided to the focus detection device 111 by the sub mirror 110, and the focus detection operation of a known phase difference detection method is performed by the focus detection device 111.

  FIG. 2 is a diagram in which the main mirror 109 and the sub mirror 110 are retracted from the subject optical path 117 that has passed through the photographing lens 102. When the photographer 115 presses a release switch (not shown) or sets the live view state by operating the imaging apparatus 100 when shooting, the main mirror 109 causes the subject light flux passing through the shooting lens 102 from the viewfinder observation position. Is automatically retracted out of the subject optical path 117, and the subject image from the photographing lens 102 can be exposed to the image sensor 106.

  The focal plane shutter (hereinafter referred to as shutter) 108 includes a magnet MG-1 that opens the front curtain when energized, and a magnet MG-2 that closes the rear curtain of the shutter 108 when energized. The light flux of the subject focused by the photographing lens 102 is controlled by controlling the amount of time until the rear curtain starts running after the front curtain of the shutter 108 has run, and the image sensor 106 performs photoelectric conversion processing as a subject image. Is done. The image data after the photoelectric conversion process is recorded on a recording medium and displayed as an image on the external display device 116. The external display device 116 displays the image of the subject exposed to the image sensor 106 in real time when the imaging device 100 is in the live view state.

  FIG. 3 is a block diagram showing an electrical configuration of the imaging apparatus according to the embodiment of the present invention. In FIG. 3, the pupil division optical system 301 restricts the incident light beam so that the light beam is incident on each phase difference sensor forming a pair of focus detection pixel groups 107 b so that the pupil is divided into the target. Furthermore, the imaging apparatus 100 includes a focus detection unit 302 that detects a focus from the image shift amount of each pixel column of two types of phase difference sensors whose optical configurations are symmetrical with respect to the optical axis in the focus detection pixel group 107b. Furthermore, the imaging apparatus 100 includes a spatial frequency detection unit 303 that detects the intensity of a high-frequency component of an image signal including a plurality of pixels located in the vicinity of the focus detection pixel group 107b in the imaging pixel group 107a.

  Further, the imaging apparatus 100 performs interpolation processing by a pixel interpolation unit 310 (to be described later) based on the focus detection result using the focus detection pixel group 107b, or uses the spatial frequency detection unit 303 to perform pixel processing based on the intensity of the high frequency component. A determination switching unit 304 is provided for selecting whether the interpolation unit 310 performs the interpolation process. Furthermore, the field of view of the focus detection pixel group 107b is limited by a light shielding layer (not shown), and no color filter is provided on the light incident surface. Therefore, the level of the image signal of the focus detection pixel group 107b is different from the level of the image signal composed of a plurality of pixels (hereinafter referred to as the vicinity pixel group) located in the vicinity of the focus detection pixel group 107b in the imaging pixel group 107a. End up.

  Therefore, the imaging apparatus 100 includes a gain adjustment unit 305 that adjusts the gain of the focus detection pixel group 107b in order to bring the image signal of the focus detection pixel group 107b closer to the level of the image signal of the neighboring pixel group. Further, based on the determination of the determination switching unit 304, the imaging apparatus 100 obtains image data corresponding to the position of the phase difference sensor of the focus detection pixel group 107b based on the image signal of the imaging pixel group 107a obtained from the imaging element 106. A pixel interpolation unit 310 that generates by interpolation calculation. Furthermore, the imaging apparatus 100 includes an image processing unit 306 that performs gamma correction, white balance adjustment, resampling, and predetermined image compression encoding on the image signal output from the imaging pixel group 107a.

  Furthermore, the imaging apparatus 100 includes a display control unit 309 that performs control to display the image data output from the image processing unit 306 on the external display device 116 and a recording unit 307 that records the operation data of the photographer 115. And an operation unit 308 for receiving. In addition, the focus detection device control unit 311 receives an operation via the operation unit 308 of the photographer 115 and controls the focus detection device 111 according to a command from the CPU 101 to perform a focus detection operation of a known phase difference detection method. . The mirror control unit 312 receives an operation via the operation unit 308 of the photographer 115 and performs operation control of the main mirror 109 and the sub mirror 110 in accordance with a command from the CPU 101. The shutter control unit 313 receives an operation via the operation unit 308 of the photographer 115 and controls the operation of the shutter 108 in accordance with a command from the CPU 101.

  FIG. 4 is a diagram illustrating an arrangement of the imaging pixel group 107a and the focus detection pixel group 107b. In FIG. 4, one of the pair of phase difference sensors in the focus detection pixel group 107b is indicated as S1, and the other as S2. Further, the pixels corresponding to the focus detection pixel group 107b are emphasized by the net line processing. A pair of pixel rows in which S1 is discretely inserted and a pixel row in which S2 is discretely inserted at a predetermined interval form one distance measuring point. In FIG. 4, the first distance measuring point is shown in the upper part and the second distance measuring point is shown in the lower part. The focus detection unit 302 performs focus detection individually for each distance measuring point.

  FIG. 5 is a schematic diagram for explaining image phase shift due to focus shift. In FIG. 5, S1 and S2 are abstractly brought close to each other and indicated by points A and B. For the sake of simplicity, illustration of RGB pixels for imaging is omitted, and it is shown as if phase difference sensors are arranged. The light from a specific point of the subject is divided into a light beam (ΦLa) that enters the corresponding A through the pupil corresponding to A and a light beam (ΦLb) that enters the corresponding B through the pupil corresponding to B. , The image formed on the phase difference sensor by the light beam entering A is called an A image, and the image formed on the phase difference sensor by the light beam entering B is called a B image.

  Since these two light fluxes are from the same point, if the focus of the image pickup optical system is on the image pickup element surface, it reaches one point bundled by the same microlens (a). However, for example, if the focus is in front of x, only the change in the incident angle θ of the light beam is displaced (b). Moreover, if there is a focus in the back by x, it will shift in the reverse direction.

  FIG. 6 is a flowchart showing an autofocus operation on the imaging surface according to the present embodiment. First, in the present embodiment, there are two types of autofocus methods on the imaging surface. Among them, the focus lens 103 is finely driven (wobbled) in the optical axis direction, and the signal from the imaging pixel group 107a in the imaging element 106 is used. Based on the obtained contrast evaluation value, the first AF method is used for focus detection based on contrast, and signals from the focus detection pixel group 107b discretely arranged in the image sensor 106 are detected, and a pair of subjects is detected. When an image is photoelectrically converted by the focus detection pixel group 107b, a pair of image signals is obtained. Each of the pair of image signals is hereinafter referred to as an A image and a B image. A method of performing phase difference AF on the imaging surface by taking a correlation between the A image and the B image is a second AF method.

  In FIG. 6, the imaging apparatus 100 starts the imaging operation in accordance with the AF start operation of the photographer 115 (for example, start of the live view operation). In S101, the imaging conditions of the imaging apparatus 100, such as ISO sensitivity and aperture value, are confirmed. Thereafter, in S102, information on the photographing lens 102 is acquired. Here, the photographic lens 102 has a lens ID indicating information such as a lens name and a focal length, and information on magnification at each focus position and zoom position in the lens CPU 105, and the information is obtained in S102. get. In S103, when performing the first AF method, the contrast evaluation value is acquired from the information acquired in S101 and S102 and the imaging information, and the focus lens 103 is required to perform the wobbling operation in the optical axis direction. The defocus amount (wobbling width) is calculated. First, if the F number of the photographing lens 102 is F and the allowable circle of confusion on the image sensor 106 is defined as δ, the wobbling width W can be expressed by the following equation.

  Here, k is a coefficient that determines the magnitude of the amplitude, and a numerical value of 1 or less such as 1/4 or 1/3 is often used. That is, since the coefficient k and the allowable confusion circle diameter δ are determined by the imaging apparatus 100, the wobbling width can be calculated by acquiring the current F number information of the photographing lens 102. Based on the information acquired in S101 and S102, the CPU 101 calculates the wobbling width.

  Subsequently, in S104, using the defocus amount obtained in S103 and the lens information in S102, a magnification variation amount associated with the wobbling operation is calculated. The calculation of the magnification fluctuation amount will be described with reference to FIG. FIG. 7 is a graph showing the amount of magnification variation with respect to the change in the focus position of the photographic lens 102. In FIG. 7A, a solid line represents a change in magnification due to a change in the focus position when a certain photographing lens 102 is set to a certain zoom position, and is stored as a function in the lens CPU 105. Then, although it is a linear function, it may be a curve function. A broken line is a focus peak position of the main subject. The broken line arrow is the defocus amount necessary for the wobbling operation calculated in S103. A solid line arrow indicates the amount of change in magnification when the focus lens 103 is moved by the defocus amount.

  FIG. 7B is a graph showing the amount of magnification variation with respect to a change in the focus position of the photographing lens 102 when the zoom position is changed from FIG. 7A with the same photographing lens 102 as FIG. 7A. It is. In FIG. 7B, the amount of change in magnification when the focus lens 103 is moved by the same defocus amount as in FIG. 7A is smaller than that in FIG. 7A. In this way, in the case of a zoom lens, a function representing a plurality of magnification fluctuations for a plurality of zoom positions, and in the case of a single focus lens, a function representing a single magnification fluctuation is given to the lens CPU 105 as magnification fluctuation information. The CPU 101 calculates the fluctuation amount of the magnification.

  In S105, the magnification fluctuation amount generated during the wobbling operation calculated in S104 is compared with a predetermined value. Here, the predetermined value is a magnification fluctuation amount in a range in which the magnification fluctuation due to the wobbling operation is not conspicuous in the imaging apparatus 100 being used, and an arbitrary numerical value is stored in the CPU 101 in the imaging apparatus 100 in advance. Yes. If it is determined in S105 that the amount of magnification variation is equal to or less than a predetermined value, that is, it is determined that the quality of the photographed image due to the variation in magnification does not deteriorate even if a wobbling operation is performed, the first AF method is adopted in S109 to To focus.

  On the other hand, if the magnification fluctuation amount is greater than or equal to the predetermined value in S105, that is, if the wobbling operation is performed, there is a possibility that the quality of the photographed image is deteriorated due to the magnification fluctuation, the process proceeds to S106. In S106, the AF accuracy is confirmed when the second AF method is performed. With respect to the accuracy confirmation method, in this embodiment, an S level (SELECTLEVEL) value disclosed in Japanese Patent Application Laid-Open No. 2007-052072 is used as an evaluation value indicating reliability, which is obtained using information on a pair of image signals. SL is used. The S level value SL is a value using, as parameters, a matching degree U, a number of edges (correlation change ΔV), a sharpness SH, and a light / dark ratio PBD as a pair of image signals. It is expressed as

  Note that the information related to the pair of image signals may not necessarily be information related to both of the pair of image signals, and may be information related to any one of the image signals. Further, the degree of coincidence U, the correlation change amount ΔV, the sharpness SH, and the contrast ratio PBD may be paraphrased as information obtained from a pair of image signals.

  Here, the degree of coincidence U is higher in reliability as the value is smaller. The larger the value of the correlation change amount ΔV, the higher the reliability. The sharpness SH is more reliable as the value thereof is larger. The greater the value of the light / dark ratio PBD, the higher the reliability. Therefore, by defining the degree of coincidence U as the numerator and the product of the correlation change amount ΔV, the sharpness SH, and the light / dark ratio PBD as the denominator, the S level value SL is defined to be small when the reliability is high for each parameter. doing.

  The coincidence degree U will be described. When a pair of subject images is photoelectrically converted by the focus detection pixel group 107b, a pair of image signals is obtained. Each of the pair of image signals is hereinafter referred to as an A image and a B image. Here, for easy understanding of the degree of coincidence, a case where unnecessary light such as ghost light is incident on one of the A and B images and the A and B images do not have the same shape will be described. Since the A image and the B image have different shapes, a portion that does not match even in a focused state is generated. The area of this non-matching part is defined as the matching degree.

  When the number of light receiving elements in the focus detection pixel group 107b is N, and the outputs of the i-th pixel of the A image and the B image at the time of focusing are a [i] and b [i], the matching degree U is as follows: I can express.

  As shown in Expression (1), the degree of coincidence between the A image and the B image can be accurately expressed by defining the absolute sum of the pixel output differences between the A image and the B image as the coincidence degree U. When the coincidence between the A image and the B image is low, the coincidence U increases, and when the coincidence between the A image and the B image is high, the coincidence U decreases.

  Next, the number of edges, that is, the correlation change amount ΔV will be described. The correlation change amount calculated in the correlation calculation is used as a parameter indicating the number of edges. The amount of change in the correlation amount between the A image and the B image in a state shifted by one pixel from the in-focus state with respect to the correlation amount between the A image and the B image in the focused state corresponds to the correlation change amount. When the correlation amount between the A image and the B image in the focused state is V1, and the correlation amount between the A image and the B image in the state shifted by one pixel from the focused state is V2, the correlation change amount ΔV is as follows: Is required.

  The correlation change amount ΔV is an area of a non-matching portion generated by shifting from a state where the edges of the A image and the B image are shifted from a state where they are shifted by one pixel from the focused state. For this reason, when the number of edges of the A image and the B image increases, the area of the non-matching portion caused by the deviation also increases. From this, it is understood that the correlation change amount ΔV is appropriate as a parameter representing the number of edges. Note that the shift amount may be larger than one pixel.

  Next, the sharpness SH will be described. The sharpness referred to in the present embodiment represents whether the value changes sharply or gradually when the signal values of the A and B images change from a certain bottom value to a peak value. In the present embodiment, the sharpness is a ratio between the primary contrast evaluation value C1 and the secondary contrast evaluation value C2 obtained from the A image and the B image. The primary contrast evaluation value is the sum of absolute values of output differences between adjacent pixels in the A and B images, and the secondary contrast evaluation value is the sum of squares of output differences between adjacent pixels in the A and B images. . When the number of pixel columns of the focus detection pixel group 107b is N and the i-th pixel outputs of the A and B images in the focused state are a [i] and b [i], the primary contrast evaluation value C1 and The secondary contrast evaluation value C2 can be expressed as follows. MAX means the larger of the two in {}.

  Since the primary contrast evaluation value C1 is an absolute sum of output differences between adjacent pixels, the primary contrast evaluation value C1 obtained from the edge portion of the signal waveform is gentle even if the gradation change of the edge portion is steep. Even if it exists, it will be the same if the peak value and the bottom value of the edge part are the same. For example, the primary contrast evaluation value C1 obtained from a subject in which half is white, half is black, and white and black are in contact with the boundary line, is white at one end, black at the other end, and from the white end to the black end. This is the same as the primary contrast evaluation value C1 obtained from a subject whose color changes gently.

  On the other hand, since the secondary contrast evaluation value C2 is the sum of squares of the output differences of adjacent pixels, what is obtained from the edge portion where the gradation change is steep is more than that obtained from the edge portion where the gradation change is gentle. growing. This is also clear from equation (6). For this reason, it is appropriate to estimate the magnitude of the gradation change of the edge portion based on the secondary contrast evaluation value C2. When the sharpness of the subject image is SH, the sharpness SH can be expressed as a ratio of the primary contrast evaluation value C1 and the secondary contrast evaluation value C2 as follows.

  Here, the reason why the sharpness SH is not expressed by the secondary contrast evaluation value C2 and is divided by the primary contrast evaluation value C1 is to remove the influence of the number of edges. For example, C2_1 is a secondary contrast evaluation value obtained from a subject in which half is white, half is black, and white and black are bordered by a boundary line, both ends are black, the center is white, and white and black are two boundary lines. Let C2_2 be the secondary contrast evaluation value obtained from the subject that is in contact with.

  Sharpness represents whether the value changes sharply or gradually when the A image and B image change from a certain bottom value to a peak value. Whether it is one or two, it should be the same value. Now, the following relationship is established between the secondary contrast evaluation value C2_1 and the secondary contrast evaluation value C2_2.

  As shown in Expression (8), the secondary contrast evaluation value C2 increases as the number of edges increases. Therefore, it is inappropriate to express the sharpness only by the secondary contrast evaluation value C2. Therefore, in order to eliminate the influence of the number of edges, normalization is performed by dividing by the primary contrast evaluation value C1. C1_1 is a primary contrast evaluation value obtained from a subject in which half is white, half is black, and white and black meet at the boundary, black at both ends, white at the center, and white and black meet at two boundaries If the primary contrast evaluation value obtained from such a subject is C1_2, the following relationship is established.

  In addition, the sharpness obtained from a subject in which half is white, half is black, and white and black are in contact with the boundary line is SH_1, both ends are black, the center is white, and white and black are in contact with two boundary lines. When the sharpness obtained from such a subject is SH_2, it can be expressed as follows.

  When Expression (8) and Expression (9) are substituted into Expression (11), SH_2 can be expressed as follows.

  From equation (12), sharpness SH_1 obtained from a subject in which half is white, half is black, and white and black are in contact with the border, and two borders are black at both ends, white at the center, and white and black It can be seen that the sharpness SH_2 obtained from the subject in contact with is the same. From the same consideration, it can be seen that the value of the sharpness SH does not change no matter how many edges are added.

  From the above, the sharpness of the subject image can be accurately expressed by setting the ratio between the primary contrast evaluation value and the secondary contrast evaluation value as sharpness.

  Next, the light / dark ratio PBD will be described. The brightness / darkness ratio PBD referred to in the present embodiment is a parameter indicating whether the density of the subject image is clear. Specifically, it indicates how much the height from the bottom value to the peak value of the subject image (signal value) is larger than the height from the dark value to the peak value of the sensor output. Yes.

  The dark value, bottom value, and peak value of the A image in the focused state are DARK_A, BOTTOM_A, and PEAK_A, respectively, and the dark value, bottom value, and peak value of the B image are DARK_B, BOTTOM_B, and PEAK_B. In this case, the light / dark ratio PBD_A obtained from the A image and the light / dark ratio PBD_B obtained from the B image can be expressed as follows.

  Of the light / dark ratios obtained from the A and B images as described above, the larger one is defined as the light / dark ratio PBD.

  According to the light / dark ratio PBD shown in Expression (15), the height from the bottom value to the peak value of the subject image becomes larger than the height from the dark value to the peak value of the sensor output. Can be expressed. As can be seen from Equation (15), the light / dark ratio PBD is a number between 0 and 1. When the light / dark ratio PBD is close to 1, it means that the height from the bottom value to the peak value of the subject image is substantially the same as the height from the dark value to the peak value of the sensor output. In this case, it is determined that the subject image is clear.

  On the contrary, when the contrast ratio is close to 0, it means that the height from the bottom value to the peak value is very small compared to the height from the dark value to the peak value. In this case, it is determined that the subject is not clear.

  As described above, by using the light / dark ratio PBD calculated based on the dark value, the bottom value, and the peak value of the subject image, it can be accurately determined whether or not the subject image is clear.

  In the present embodiment, the accuracy of the phase difference AF can be determined by using the above-described S level value SL as the reliability evaluation value. That is, if it is determined that the reliability is high using the S level value SL, the subject at that time should be able to obtain a highly accurate in-focus state even if the second AF method is used. Therefore, by using the S level value SL as the accuracy determination value of the second AF method, the AF accuracy of the second AF method is determined.

  In S107, the result of the accuracy check of the second AF method in S106 is received, and it is determined whether the accuracy, that is, the S level value SL is equal to or greater than a predetermined value. The predetermined value here is AF accuracy in a range where the main subject is not blurred, and an arbitrary numerical value is stored in advance in the CPU 101 in the imaging apparatus 100 and compared. If it is determined in S107 that the accuracy of the second AF method is within a predetermined value, that is, it is possible to focus on the main subject with high accuracy, the operation of the second phase difference AF is started in S107, and the subject is moved to the subject. And focus on. If it is determined in S107 that the accuracy of the second AF method is equal to or lower than a predetermined value, that is, the main subject may not be in focus, priority is given to focus detection, and the calculation in S103 is performed in S109. The focusing operation in the first AF method is started with the defocus amount necessary for wobbling, and focusing is performed.

  In the present embodiment, when the amount of magnification fluctuation is large in the flowchart S105 of FIG. 6 and the accuracy of the second AF method becomes NG in S107, priority is given to focusing with the first AF method. However, the user may be warned.

  In this embodiment, when AF on the imaging surface is performed, the magnification fluctuation at the time of focus drive is calculated, and when the magnification fluctuation is small, a good image in focus can be acquired by performing a wobbling operation. When the magnification fluctuation is large, the imaging surface phase difference AF is used, and it is possible to focus and perform the focusing operation speedily.

100 Imaging device 101 CPU
102 Shooting Lens 103 Focus Lens 105 Lens CPU
106 Imaging element 107a Imaging pixel group 107b Focus detection pixel group 302 Focus detection unit

Claims (4)

In the imaging apparatus (100) that forms an image of a subject on the imaging element (106) by the imaging optical system (102) and generates an image representing the subject, the imaging optical system (102) performs focus adjustment by movement. A focus lens (103) is included, the focus position is detected by detecting the contrast of the image obtained by the image sensor (106) while moving the focus lens (103), and the wobbling operation is performed. A first focus detection means using contrast AF having a wobbling mode for detecting the in-focus position by moving the focus lens (103) in the in-focus direction while recognizing the in-focus direction; Second focus detection means by discretely arranged focus detection pixels,
When the magnification variation of the photographing optical system due to the wobbling operation of the first focus detection unit is smaller than a predetermined range, the focus detection by the first focus detection unit is performed, and the magnification variation of the photographing optical system is within the predetermined range. If larger, an imaging apparatus that performs focus detection by the second focus detection means. The imaging apparatus according to claim 1, wherein a magnification fluctuation amount associated with a wobbling operation is calculated from an aperture (104) and magnification fluctuation information of the photographing optical system (102). The focus detection accuracy by the second focus detection means is determined, and when the accuracy of the second focus detection method is equal to or greater than a predetermined value, the accuracy of focus detection by the second focus detection means is less than a predetermined value. The imaging apparatus according to claim 1, wherein focus detection is performed by the first focus detection unit. The focus detection accuracy by the second focus detection means is determined, and when the accuracy of the second focus detection method is equal to or greater than a predetermined value, the accuracy of focus detection by the second focus detection means is less than a predetermined value. The imaging apparatus according to claim 1, wherein a warning display is performed.