JP2014238517A - Imaging device, imaging system, imaging device control method, program, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device capable of ensuring highly reliable and high speed focus detection by setting an appropriate diaphragm value depending on a defocus amount.SOLUTION: An imaging device comprises: an imaging element photoelectrically converting an optical image via an imaging optical system; focus detection means detecting a focus by phase difference scheme on the basis of an image signal obtained from a focus detection pixel of the imaging element, and calculating a defocus amount; diaphragm value setting means setting a diaphragm value within a predetermined range excluding an open diaphragm value depending on the defocus amount calculated by the focus detection means; and control means controlling a diaphragm to have the diaphragm value set by the diaphragm value setting means to exert focusing control.

Description

  The present invention relates to an imaging apparatus that performs focus detection.

  Patent Document 1 discloses a focus detection apparatus using a pupil division method (phase difference method) using a CMOS sensor. The pupil-division focus detection device can detect the defocus amount by a single measurement even in a largely blurred state. Therefore, high-speed focus adjustment is possible, which is a promising method. The reason why the defocus amount can be detected by one measurement is that the shift amount and shift direction of two image signals generated by pupil division can be detected.

  Patent Document 2 discloses an imaging apparatus that performs focus detection by controlling the aperture with an aperture value larger than the open aperture value in order to improve the detection accuracy of the defocus amount.

Japanese Unexamined Patent Publication No. 01-216306 JP 2008-242182 A

  However, when the pupil division type focus detection device does not have sufficient pupil division performance, the defocus amount detectable range and the reliability of the focus detection result greatly differ depending on the aperture value. For this reason, high-speed focus detection may not be performed.

  Therefore, the present invention provides an imaging apparatus, an imaging system, an imaging apparatus control method, a program, and a storage medium that can perform high-reliability and high-speed focus detection by setting an appropriate aperture value according to the defocus amount. I will provide a.

  An imaging apparatus according to an aspect of the present invention includes an imaging element that photoelectrically converts an optical image via an imaging optical system, and focus detection by a phase difference method based on an image signal obtained from a focus detection pixel of the imaging element. A focus detection unit that calculates a defocus amount, and an aperture value setting unit that sets an aperture value within a predetermined range that does not include an open aperture value according to the defocus amount calculated by the focus detection unit And a control unit that performs focusing control by controlling the aperture so as to be the aperture value set by the aperture value setting unit.

  An imaging system as another aspect of the present invention includes a lens device including an imaging optical system and the imaging device.

  According to another aspect of the present invention, there is provided a method for controlling an imaging apparatus, the step of photoelectrically converting an optical image through an imaging optical system, and a phase difference method based on an image signal obtained from a focus detection pixel of an imaging element. Performing focus detection, calculating a defocus amount, setting an aperture value within a predetermined range that does not include an open aperture value according to the calculated defocus amount, and the set aperture value And controlling the aperture so as to achieve focusing control.

  A program according to another aspect of the present invention is configured to cause a computer to execute the control method of the imaging apparatus.

  A storage medium according to another aspect of the present invention stores the program.

  Other objects and features of the present invention are illustrated in the following examples.

  According to the present invention, an imaging device, an imaging system, an imaging device control method, a program, and a storage capable of performing high-reliability and high-speed focus detection by setting an appropriate aperture value according to the defocus amount A medium can be provided.

It is a block diagram which shows the structure of the imaging device in a present Example. It is a figure which shows the pixel structure in a present Example. It is explanatory drawing of the pupil division function of the image pick-up element in a present Example. It is explanatory drawing of the pupil intensity distribution and a line image in a present Example. In this example, it is explanatory drawing of a pupil intensity distribution and a line image in case an aperture value is small. In this example, it is explanatory drawing of a pupil intensity distribution and a line image in case an aperture value is large. In this example, it is explanatory drawing of the dispersion | variation in the calculation defocus amount by the difference in a to-be-photographed object. In the present embodiment, it is an explanatory diagram of the variation in the calculated defocus amount under the same subject condition. It is explanatory drawing of the method of calculating | requiring the minimum value of an aperture value in a present Example. It is explanatory drawing of the method of calculating | requiring the maximum aperture value in a present Example. It is a block diagram which shows the structure which performs the focus detection in a present Example. 3 is a flowchart of a focus detection method in the first embodiment. 6 is a flowchart of a focus detection method in Embodiment 2.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

(Configuration of imaging system)
First, an imaging apparatus (imaging system) in an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus (imaging system 100) in the present embodiment. The imaging system 100 of this embodiment is a digital camera system that includes an imaging device (camera body) and a lens device (interchangeable lens) that can be attached to and detached from the imaging device.

  The first lens group 101 is disposed in the forefront (subject side) of the plurality of lens groups constituting the photographing lens (imaging optical system), and can advance and retreat in the direction of the optical axis OA (optical axis direction). The lens barrel is held in a state. The aperture / shutter 102 (aperture) adjusts the aperture to adjust the amount of light during shooting, and also functions as an exposure time adjustment shutter during still image shooting. The second lens group 103 has a zoom function of moving forward and backward in the optical axis direction integrally with the diaphragm / shutter 102 and performing a zooming operation in conjunction with the forward / backward movement of the first lens group 101. The third lens group 105 is a focus lens group that performs focus adjustment (adjustment of defocus amount) by moving forward and backward in the optical axis direction. The optical low-pass filter 106 is an optical element for reducing false colors and moire in the captured image.

  The image sensor 107 performs photoelectric conversion of a subject image (optical image) via an imaging optical system, and includes, for example, a CMOS sensor or a CCD sensor and its peripheral circuits. As the image sensor 107, for example, a two-dimensional single-plate color sensor in which a Bayer array primary color mosaic filter is formed on-chip on a light receiving pixel having m pixels in the horizontal direction and n pixels in the vertical direction is used. It is done.

  The lens ROM 110 (storage means) stores unique data (lens information such as lens ID and exit pupil distance) for each interchangeable lens that can be attached to and detached from the camera body. The lens information stored in the lens ROM 110 is provided to a later-described CPU 121 (central processing unit) by communication when performing focus detection or the like.

  The zoom actuator 111 performs a zooming operation by moving the first lens group 101 and the second lens group 103 along the optical axis direction by rotating (driving) a cam cylinder (not shown). The aperture shutter actuator 112 controls the aperture diameter of the aperture / shutter 102 to adjust the amount of light (photographing light amount), and also controls the exposure time during still image shooting. The focus actuator 114 adjusts the focus by moving the third lens group 105 in the optical axis direction.

  The electronic flash 115 is an illumination device used to illuminate a subject. As the electronic flash 115, a flash illumination device including a xenon tube or an illumination device including an LED (light emitting diode) that continuously emits light is used. The AF auxiliary light unit 116 projects an image of a mask having a predetermined opening pattern onto the object field via a light projection lens. As a result, the focus detection capability for a dark subject or a low-contrast subject can be improved.

  The CPU 121 is a control unit that performs various controls of the imaging apparatus (camera body). The CPU 121 includes a calculation unit, a ROM, a RAM, an A / D converter, a D / A converter, a communication interface circuit, and the like. The CPU 121 drives each unit by reading and executing a predetermined program stored in the ROM, and controls a series of operations such as focus detection, photographing, image processing, or recording.

  The CPU 121 includes an aperture value switching unit 121a (aperture value setting unit) and a focus detection unit 121b. The focus detection unit 121b performs focus detection by a phase difference method based on an image signal obtained from the focus detection pixel of the image sensor 107, and calculates a defocus amount. The aperture value switching unit 121a sets the aperture value (F value) within a predetermined range that does not include the full aperture value, according to the defocus amount calculated by the focus detection unit 121b. Then, the CPU 121 performs focusing control by controlling the diaphragm / shutter 102 (aperture) so that the diaphragm value set by the diaphragm value switching unit 121a is obtained.

  The electronic flash control circuit 122 controls lighting of the electronic flash 115 in synchronization with the photographing operation. The auxiliary light driving circuit 123 performs lighting control of the AF auxiliary light unit 116 in synchronization with the focus detection operation. The image sensor driving circuit 124 controls the image capturing operation of the image sensor 107, A / D converts the acquired image signal, and transmits it to the CPU 121. The image processing circuit 125 performs processing such as γ (gamma) conversion, color interpolation, or JPEG (Joint Photographic Experts Group) compression of image data acquired from the image sensor 107.

  The focus driving circuit 126 (driving means) drives the focus actuator 114 based on the focus detection result, and moves the third lens group 105 along the optical axis direction to adjust the defocus amount (defocus amount). To do. The aperture shutter drive circuit 128 drives the aperture shutter actuator 112 to control the aperture diameter of the aperture / shutter 102. A combination of the aperture shutter actuator 112 and the aperture shutter drive circuit 128 is an aperture control means.

  The zoom drive circuit 129 drives the zoom actuator 111 according to the zoom operation of the photographer. The focus driving circuit 126, the aperture shutter driving circuit 128, and the zoom driving circuit 129 are each connected to the CPU 121 in the imaging apparatus (camera body) via the terminal 130 (communication unit).

  The display 131 includes, for example, an LCD (Liquid Crystal Display). The display 131 displays information related to the shooting mode, a preview image before shooting, a confirmation image after shooting, a focus state display image at the time of focus detection, and the like. The operation unit 132 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. The release switch has a two-stage switch in a half-pressed state (a state where SW1 is ON) and a full-pressed state (a state where SW2 is ON). The recording medium 133 is, for example, a flash memory that can be attached to and detached from the imaging apparatus, and records captured images (image data).

(Image sensor structure)
Next, the pixel structure of the image sensor 107 in this embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating a pixel structure of the image sensor 107. 2A is an explanatory diagram of a pixel array of the image sensor 107, FIG. 2B is an enlarged view of the pixel 210G in FIG. 2A, and FIG. 2C is a line a in FIG. -A shows cross-sectional views, respectively.

  FIG. 2A shows a pixel array of the image sensor 107 (two-dimensional CMOS sensor) in a pixel range of 4 rows × 4 columns. The arrangement of the pixels 210 is 2 rows × 2 columns, and a Bayer arrangement is adopted. As the two pixels in the diagonal direction, a pixel 210G having a spectral sensitivity of G (green) is arranged. Further, as the other two pixels, a pixel 210R having a spectral sensitivity of R (red) and a pixel 210B having a spectral sensitivity of B (blue) are respectively arranged. The pixels 210R, 210G, and 210B have two subpixels 201a and 201b for pupil division, respectively. The sub-pixel 201a is a first pixel that receives the light beam that has passed through the first pupil region of the imaging optical system. The sub-pixel 201b is a second pixel that receives the light beam that has passed through the second pupil region of the imaging optical system. Each pixel functions as an imaging pixel and a focus detection pixel.

  Regarding the coordinate axes indicated by x, y, and z in FIG. 2B, the xy plane is located within the paper surface of FIG. 2B, and the z axis is an axis perpendicular to the paper surface. The subpixels 201a and 201b are arranged along a direction parallel to the x axis.

  Regarding the coordinate axes indicated by x, y, and z in FIG. 2C, the xz plane is located in the plane of FIG. 2C, and the y axis is an axis perpendicular to the plane of the paper. The detection unit includes a photodiode including a p-type layer 200 and an n-type layer. The micro lens 202 is arranged at a position away from the light receiving surface by a predetermined distance in the z-axis direction (the direction of the optical axis OA). The microlens 202 is formed on the wiring layer 203.

  In the present embodiment, all pixels 210R, 210G, and 210B of the image sensor 107 are provided with pupil-dividing sub-pixels 201a and 201b. The sub-pixels 201a and 201b are used as focus detection pixels. However, the present embodiment is not limited to this, and the configuration may be such that focus detection pixels that can be divided into pupils are provided in only some of the pixels.

(Concept of pupil division function by image sensor)
Next, the pupil division function of the image sensor 107 will be described with reference to FIG. FIG. 3 is an explanatory diagram of the pupil division function of the image sensor 107 and shows a state of pupil division in one pixel unit.

  With respect to the coordinate axes (x, y, z) of the pixel portion shown in the lower part of FIG. 3, the xz plane is located within the paper surface of FIG. 3, and the y axis is an axis perpendicular to the paper surface. The pixel includes a p-type layer 300 and n-type layers 301a and 301b. The p-type layer 300 and the n-type layer 301a constitute the subpixel 201a in FIG. 2, and the p-type layer 300 and the n-type layer 301b constitute the subpixel 201b. The microlens 304 is disposed on the z axis.

  In addition, an exit pupil 302 and a frame 303 (for example, a diaphragm frame or a lens frame) are shown in the upper part of FIG. Regarding the coordinate axes (x, y, z) shown in the upper part of FIG. 3, the xy plane is located in the plane of FIG. 3, and the z axis is an axis perpendicular to the plane of the paper.

  One sub-pixel is formed by providing n-type layers 301 a and 301 b embedded in the p-type layer 300 in one pixel. The two subpixels are regularly arranged along the x direction. Further, since the two sub-pixels are decentered in the + x direction and the −x direction, pupil division can be performed using one microlens 304. In FIG. 3, as the exit pupil 302, a pupil 302a of the image signal A and a pupil 302b of the image signal B are shown. The image signal A is a first image signal acquired by a subpixel corresponding to the n-type layer 301a eccentric in the −x direction. The image signal B is a second image signal acquired by a subpixel corresponding to the n-type layer 301b eccentric in the + x direction.

  As described above, in this embodiment, the image signal A (first signal) is obtained by regularly arranging a plurality of subpixels 301a in the x direction as shown in FIG. It is the obtained signal. That is, the image signal A is one of image signals obtained from a pair of light fluxes that pass through different exit pupil regions of the imaging optical system and have different baseline lengths depending on the aperture value. Further, the image signal B (second signal) is a signal obtained from a plurality of subpixels 301b in which a plurality of subpixels 301b are regularly arranged in the x direction as shown in FIG. . That is, the image signal B is the other of the image signals obtained from a pair of light fluxes that pass through different exit pupil regions of the imaging optical system and have different baseline lengths depending on the aperture value.

  The CPU 121 can obtain the focal position of the photographing lens by calculating the defocus amount from the relative image shift amount between the image signal A and the image signal B using a correlation calculation. This makes it possible to adjust the defocus amount of the photographic lens. In the present embodiment, the configuration corresponding to the subject having the luminance distribution in the x direction has been described. However, the present embodiment can also adopt a configuration corresponding to a subject having a luminance distribution in the y direction by developing the same configuration in the y direction.

(Asymmetry between vignetting and line image)
Subsequently, the pupil intensity distribution and the line image in the present embodiment will be described with reference to FIGS. FIG. 4 is an explanatory diagram of pupil intensity distribution and line images. 4A shows a pupil intensity distribution 401a related to the image signal A (A image), and FIG. 4B shows a pupil intensity distribution 401b related to the image signal B (B image). 4C is a cross-sectional view (line images 402a and 402b) along the x-axis direction of the pupil intensity distributions 401a and 401b of the image signals A and B shown in FIGS. 4A and 4B. Each is shown.

  FIG. 5 is an explanatory diagram of the pupil intensity distribution and the line image when the aperture value is small (when the aperture diameter is large). FIG. 5A shows a state (pupil intensity distribution 501a) in which the pupil intensity distribution related to the image signal A is vignetted in the frame 503 (aperture frame) when the aperture value is small (when the aperture diameter is large). Yes. FIG. 5B shows a state in which the pupil intensity distribution related to the image signal B is vignetted in the frame 503 when the aperture value is small (pupil intensity distribution 501b). FIG. 5C is a cross-sectional view (line images 502a and 502b) along the x-axis direction of the pupil intensity distributions 501a and 501b of the image signals A and B shown in FIGS. 5A and 5B. Show.

  As can be seen by comparing FIG. 4C and FIG. 5C, when the aperture value is small, with respect to the line image 502a, on the −x side, the effect of vignetting by the frame 503 (aperture frame) is large, so a steep curve is obtained. On the other hand, since the influence of the frame 503 is small on the + x side, the curve becomes a gentle curve. Thus, when the aperture value is small, the line image 502a has an asymmetric shape with respect to the optical axis. The line image 502b also has an asymmetric shape, similar to the line image 502a, except that the polarity of the line image 502a is reversed.

  FIG. 6 is an explanatory diagram of the pupil intensity distribution and the line image when the aperture value is large (when the aperture diameter is small). FIG. 6A shows a state (pupil intensity distribution 601a) in which the pupil intensity distribution related to the image signal A is vignetted in the frame 603 (aperture frame) when the aperture value is large (when the aperture diameter is small). Yes. FIG. 6B shows a state in which the pupil intensity distribution related to the image signal B is vignetted by the frame 603 when the aperture value is large (pupil intensity distribution 601b). 6C is a cross-sectional view (line images 602a and 602b) along the x-axis direction of the pupil intensity distributions 601a and 601b of the image signals A and B shown in FIGS. 6A and 6B. Show.

  As shown in FIG. 6C, when the aperture value is large, the line image 602a has a steep curve on both the −x side and the + x side because the influence of vignetting by the frame 603 (aperture frame) is large. Thus, when the aperture value is large, the line image 602a has a symmetrical shape with respect to the optical axis. Similarly, the line image 602b has a symmetrical shape.

  As shown in FIG. 6, when the line image has a symmetric shape, the image signals A and B output from the image sensor 107 have waveforms having substantially the same shape with respect to different subjects. For this reason, even when the subject changes, the set defocus amount (actual defocus amount) and the calculated defocus amount (defocus amount calculated by the correlation calculation) are close to each other. On the other hand, when the line image has an asymmetric shape as shown in FIG. 5C, the image signals A and B output from the image sensor 107 also have an asymmetric shape. The difference with the amount becomes larger.

  Next, with reference to FIG. 7, the variation in the calculated defocus amount due to the difference in subject will be described. FIG. 7 is an explanatory diagram of variations in the calculated defocus amount due to differences in subjects, and shows the relationship between the set defocus amount and the calculated defocus amount. In FIG. 7, the solid line relates to the subject A and the broken line relates to the subject B, and shows the relationship between the set defocus amount and the calculated defocus amount, respectively. A one-dot chain line indicates a case where the set defocus amount and the calculated defocus amount have the same value. For example, when the set defocus amount is D1, the calculated defocus amount for the subject A is D3, and the calculated defocus amount for the subject B is D2. That is, even if the set defocus amount D1 is the same, a variation V (= D3−D2) in the calculated defocus amount due to a difference in subjects (subjects A and B) occurs.

  As described above, when the aperture value is small when performing focus detection by the pupil division method (phase difference method), the line image is easily distorted and becomes an asymmetric shape due to the influence of vignetting by the frame (aperture frame, lens frame, etc.). Also, when the aperture value is small, the image signal is likely to spread, and as shown in FIG. 7, the variation in the calculated defocus amount due to the difference in the subject increases as the set defocus amount increases.

(Baseline length)
Next, with reference to FIG. 8, a variation in the calculated defocus amount for the same subject will be described. FIG. 8 is an explanatory diagram of variations in the calculated defocus amount with respect to the same subject (subject A), and shows the relationship between the set defocus amount and the calculated defocus amount.

  When performing focus detection by the pupil division method (phase difference method), as can be seen by comparing the line images 502a and 502b in FIG. 5C and the line images 602a and 602b in FIG. As the line length increases, the base line length (the center of gravity distance between the line images of the image signals A and B) becomes shorter. If the baseline length is short, the sensitivity increases. For this reason, as shown in FIG. 8, even if the subject conditions (the same subject, the same set defocus amount, etc.) are affected by the influence of S / N or the like, the calculated defocus amount varies. Becomes larger.

  On the other hand, when the aperture value is increased, the signal of the subject image (image signal) is reduced, and it becomes easy to ensure a sufficient field length. For this reason, the variation in the calculated defocus amount due to the difference in the subject is reduced, and the defocus amount detectable range is widened.

(Method for determining F value in direction discrimination region)
As described above, in the vicinity of focusing (a range where the calculated defocus amount is small), the smaller the aperture value, the higher the reliability of the calculated defocus amount. On the other hand, outside the in-focus vicinity (range where the calculated defocus amount is large), the reliability of the calculated defocus amount is higher when the aperture value is increased within a range where variations of the same subject can be tolerated. As an aperture value setting method for obtaining a highly reliable calculated defocus amount other than in the vicinity of in-focus, there is a method using the shape of the pupil intensity distribution.

  9 is the same cross-sectional view as FIG. 4C, and the line images 902a and 902b correspond to the line images 402a and 402b in FIG. 4C, respectively. The straight line region shown in FIG. 9 is a region where the amount of change in the inclination of each of the line images 902a and 902b is small. When the frame (aperture frame) is set within the straight line region, the asymmetry of the line image is reduced. For this reason, it is preferable to determine the aperture value (minimum aperture value) within a range in which the frame (aperture frame) falls within the linear region.

  On the other hand, the size of the frame (aperture frame) on the pupil plane is determined by the aperture value and the pupil distance. For this reason, the minimum aperture value differs depending on the type of lens. Therefore, when it is necessary to assume a plurality of lenses such as an interchangeable lens, only one minimum aperture value may be set in consideration of the difference in lens type, or the aperture value may be set for each lens type. A minimum value (a minimum value of an aperture value that differs for each lens) may be set. In addition, since the straight line region changes according to the shape of the pupil intensity distribution, the minimum value of the aperture value is also different if the sensor has a different pupil intensity distribution.

  In order to further reduce the difference in the calculated defocus amount due to the difference in the subject, when setting the aperture value to be larger than the minimum value of the aperture value, the aperture value is set in consideration of variations in the calculated defocus amount for the same subject. It is preferable to determine. One of the methods is a method of setting the maximum aperture value so that the signs of the set defocus amount and the calculated defocus amount are not reversed except in the vicinity of the in-focus state in consideration of variations in the same subject. .

  FIG. 10 is an explanatory diagram of a method for obtaining the maximum aperture value. As shown in FIG. 10, when the aperture value is large, the base line length is shortened, and the variation X of the calculated defocus amount for the same subject increases due to the influence of S / N or the like. If the variation X of the calculated defocus is too large, the sign of the set defocus amount and the calculated defocus amount may be reversed near the boundary near the focus (within the focus vicinity range A). If the sign is reversed in this way, the determination of the defocus direction is wrong and the focus adjustment is performed in the wrong direction. Therefore, it is preferable to set the aperture value smaller than the aperture value when the variation X of the calculated defocus amount for the same subject matches the in-focus range A (X = A) as the maximum aperture value. Note that the variation in the calculated defocus amount for the same subject can be calculated based on the variation in the calculated defocus amount by photographing the reference subject a plurality of times.

(Focus detection)
Next, a configuration for performing focus detection by switching the aperture value in accordance with the calculated defocus amount will be described with reference to FIG. FIG. 11 is a block diagram illustrating a configuration for performing focus detection.

  As shown in FIG. 11, the CPU 121 includes an aperture value switching unit 121a and a focus detection unit 121b. The image sensor 107 photoelectrically converts a subject light beam obtained via the imaging optical system (third lens group 105) and outputs an image signal. The focus detection unit 121b performs focus detection by correlation calculation using the image signal from the image sensor 107, and outputs a calculated defocus amount. The focus detection unit 121b outputs a drive control signal based on the focus detection result (calculated defocus amount). The focus drive circuit 126 calculates a focus drive amount based on the drive control signal, and drives and controls a part of the imaging optical system (third lens group 105).

  The aperture value switching unit 121a switches the aperture value based on the calculated defocus amount output from the focus detection unit 121b (sets the aperture value according to the calculated defocus amount). For example, in the present embodiment, the aperture value switching unit 121a sets the first aperture value when the calculated defocus amount is greater than or equal to the first threshold (other than the focus vicinity) or the calculated defocus amount is not stored. Signal (aperture value information) is output. On the other hand, when the calculated defocus amount is smaller than the first threshold (near the in-focus state), the aperture value switching unit 121a outputs a signal for setting the second aperture value.

  The aperture shutter drive circuit 128 (aperture control means) is configured to detect an aperture (a combination of apertures) based on aperture value information (a signal for setting the first aperture value or the second aperture value) output from the aperture value switching unit 121a. The shutter 102) is controlled.

(Embodiment 1)
Next, with reference to FIG. 12, a control method (focus detection method) of the imaging apparatus according to the first embodiment of the present invention will be described. FIG. 12 is a flowchart of the focus detection method in the present embodiment, and shows a method of performing focus detection by switching the aperture value according to the calculated defocus amount. Each step in FIG. 12 is executed based on a command from the CPU 121.

  When focus detection starts, first in step S1201, the aperture value switching unit 121a switches the aperture value according to the calculated defocus amount, that is, the aperture value (first aperture value or second aperture value) according to the calculated defocus amount. (Aperture value) is set. For example, the calculated defocus amount is compared with the first threshold value, and the aperture value is set (switched) according to the result. At this time, the aperture value switching means 121 a outputs aperture value information indicating the aperture value to be set to the aperture shutter drive circuit 128 to the aperture shutter drive circuit 128.

  Subsequently, in step S1202, after the aperture value switching unit 121a switches the aperture value (performs aperture control), the image sensor 107 performs photoelectric conversion on the light beam obtained via the imaging optical system, Image signals (image signals A and B) are output. The focus detection unit 121b acquires the image signals A and B output from the image sensor 107. In step 1203, the focus detection unit 121b performs focus detection. That is, the focus detection unit 121b performs a correlation calculation using the image signals A and B, and outputs a drive control signal and a calculated defocus amount.

  In step S1204, the focus detection unit 121b determines whether focus detection is completed, that is, whether an in-focus state is obtained. If focus detection has not been completed, the process returns to step S1201, and steps S1201 to S1204 are repeated. On the other hand, when the focus detection is completed, this flow ends.

  As described above, in the present embodiment, the aperture value switching unit 121a (aperture value setting unit) is a predetermined value that does not include the full aperture value according to the defocus amount (calculated defocus amount) calculated by the focus detection unit 121b. Set the aperture value within the range.

  Preferably, the aperture value switching unit 121a determines whether or not the defocus amount (calculated defocus amount) is equal to or greater than a first threshold value. The aperture value switching unit 121a sets the first aperture value as the aperture value when the defocus amount is greater than or equal to the first threshold value. On the other hand, when the defocus amount is smaller than the first threshold value, a second aperture value smaller than the first aperture value is set as the aperture value. Preferably, the aperture value switching unit 121a sets the first aperture value as the aperture value when the defocus amount is not stored. More preferably, the aperture value switching unit 121a sets the aperture value according to the imaging optical system.

  Preferably, the first aperture value is set based on the pupil intensity distribution. More preferably, the first aperture value is set such that the aperture frame is within an area where the change amount of the inclination of the line image in the pupil intensity distribution is smaller than a predetermined amount. More preferably, the first aperture value is set so that the variation in the defocus amount calculated for the same subject by the focus detection unit 121b is smaller than the predetermined variation. The variation in the defocus amount is calculated, for example, by performing a plurality of shootings on the reference subject.

(Embodiment 2)
Next, with reference to FIG. 13, a control method (focus detection method) of the imaging apparatus according to the second embodiment of the present invention will be described. Since the pupil division performance is insufficient, the detection accuracy of the in-focus position may be insufficient even if the aperture value is reduced in the vicinity of the in-focus state. In this case, the focus detection is performed near the focus by focus detection using the pupil division method except near the focus, and the contrast method focus detection is performed only near the focus, so that the contrast method focus detection is performed from other than the focus vicinity. Can be achieved.

  FIG. 13 is a flowchart of the focus detection method in the present embodiment, and shows a case where the aperture value is switched according to the calculated defocus amount and both pupil division method (phase difference method) and contrast type focus detection are performed. Yes. Each step in FIG. 13 is executed based on a command from the CPU 121. Steps S1301 to S1303 in FIG. 13 are the same as steps S1201 to S1203 in FIG.

  After the focus detection unit 121b performs focus detection in step S1303, in step S1304, the CPU 121 (focus detection unit 121b) determines whether to switch from the pupil division method (phase difference method) to the contrast method focus detection. To do. Specifically, the CPU 121 determines whether or not it is in the in-focus state based on the information obtained from the focus detection unit 121b. Whether or not it is in the in-focus state is determined, for example, based on whether or not the calculated defocus amount is less than a predetermined threshold value. Here, the focus detection range by the contrast method may be controlled to be narrower. At this time, the second aperture value smaller than the first aperture value is further pursued, and when the calculated defocus amount obtained with the second aperture value becomes less than a predetermined threshold value, the process shifts to contrast-type focus detection. Configured to do.

  In step S1304, if it is not in the in-focus state (when the calculated defocus amount is greater than or equal to the second threshold value), the process returns to step S1301, and steps S1301 to S1304 are repeated (focus detection using the pupil division method (phase difference method)). I do). On the other hand, when it is in the in-focus state (when the calculated defocus amount is smaller than the second threshold value), the process proceeds to step S1305, and focus detection is performed by the contrast method.

  In step S1305, as in step S1302, the image sensor 107 photoelectrically converts the light beam obtained via the imaging optical system and outputs image signals A and B. Then, the focus detection unit 121b acquires the image signals A and B. Subsequently, in step S1306, the focus detection unit 121b performs focus detection by a contrast method. That is, the focus detection unit 121b calculates the contrast evaluation values of the image signals A and B based on the contrast of the image signals A and B.

  Subsequently, in step S1307, the focus detection unit 121b determines whether focus detection is completed, that is, whether an in-focus state is obtained. If focus detection has not been completed, the process returns to step S1305, and steps S1305 to S1307 are repeated. On the other hand, when the focus detection by the contrast method is completed, this flow ends.

  Thus, in the present embodiment, the aperture value switching unit 121a determines whether or not the defocus amount (calculated defocus amount) is equal to or greater than the second threshold value. The focus detection unit 121b performs focus detection by the phase difference method when the defocus amount is equal to or greater than the second threshold. On the other hand, when the defocus amount is smaller than the second threshold, focus detection is performed using a contrast method.

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

  According to each embodiment, an imaging device, an imaging system, an imaging device control method, a program, and an imaging device capable of highly reliable and high-speed focus detection by setting an appropriate aperture value according to the defocus amount, and A storage medium can be provided. In addition, since the calculated defocus amount with high reliability can be obtained by appropriately setting the aperture value other than in the vicinity of the in-focus state, the number of focus detections can be reduced, and high-speed focus detection can be performed.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

100 Imaging system 121 CPU
121a Aperture value switching means 121b Focus detection means

Claims (15)

An image sensor that photoelectrically converts an optical image via an imaging optical system;
Focus detection means for performing focus detection by a phase difference method based on an image signal obtained from a focus detection pixel of the image sensor and calculating a defocus amount;
An aperture value setting means for setting an aperture value within a predetermined range that does not include an open aperture value according to the defocus amount calculated by the focus detection means;
An image pickup apparatus comprising: a control unit that performs focusing control by controlling the aperture so that the aperture value set by the aperture value setting unit is obtained. The aperture value setting means includes:
Determining whether the defocus amount is greater than or equal to a first threshold;
If the defocus amount is greater than or equal to the first threshold, the first aperture value is set as the aperture value,
The imaging apparatus according to claim 1, wherein when the defocus amount is smaller than the first threshold value, a second aperture value smaller than the first aperture value is set as the aperture value. .   The imaging apparatus according to claim 2, wherein the aperture value setting unit sets the first aperture value as the aperture value when the defocus amount is not stored.   The imaging apparatus according to claim 2, wherein the aperture value setting unit sets the aperture value according to the imaging optical system.   5. The imaging apparatus according to claim 2, wherein the first aperture value is set based on a pupil intensity distribution.   6. The first aperture value is set such that the aperture frame is set within an area where the amount of change in the inclination of the line image in the pupil intensity distribution is smaller than a predetermined amount. Imaging device.   3. The first aperture value is set such that a variation in the defocus amount calculated for the same subject by the focus detection unit is smaller than a predetermined variation. The imaging device according to any one of 1 to 6.   The imaging apparatus according to claim 7, wherein the variation in the defocus amount is calculated by performing a plurality of shootings on a reference subject. The aperture value setting means determines whether the defocus amount is greater than or equal to a second threshold value,
The focus detection means includes
When the defocus amount is greater than or equal to the second threshold, focus detection is performed by the phase difference method,
The imaging apparatus according to claim 1, wherein focus detection is performed by a contrast method when the defocus amount is smaller than the second threshold value. A lens apparatus having an imaging optical system;
An imaging system comprising: the imaging device according to claim 1. Photoelectrically converting the optical image through the imaging optical system;
Performing focus detection by a phase difference method based on an image signal obtained from a focus detection pixel of an image sensor, and calculating a defocus amount;
According to the calculated defocus amount, setting an aperture value within a predetermined range that does not include an open aperture value;
And a step of performing focusing control by controlling the aperture so that the set aperture value is obtained. In the step of setting the aperture value,
Determining whether the defocus amount is greater than or equal to a first threshold;
If the defocus amount is greater than or equal to the first threshold, the first aperture value is set as the aperture value,
The imaging apparatus according to claim 11, wherein when the defocus amount is smaller than the first threshold value, a second aperture value smaller than the first aperture value is set as the aperture value. Control method. Determining whether to perform focus detection by the phase difference method or focus method by a contrast method,
Determining whether the defocus amount is greater than or equal to a second threshold;
When the defocus amount is greater than or equal to the second threshold, focus detection is performed by the phase difference method,
The method according to claim 12, wherein when the defocus amount is smaller than the second threshold, focus detection is performed by a contrast method.   A program configured to cause a computer to execute the control method for an imaging apparatus according to any one of claims 11 to 13.   A storage medium storing the program according to claim 14.