JP2014142497A - Imaging apparatus and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of obtaining high focus detection accuracy, even when using an image blur correction function.SOLUTION: A digital camera 100A eccentrically moving a second lens group 103 in a plane orthogonal to an optical axis, to correct an image blur is configured to switch focus detection means adopting a phase difference detection system, for detecting a focus on an object by using an electrical signal outputted from a pixel for focus detection included in an imaging element 106 and focus detection means adopting a contrast evaluation system, for detecting a focus position by the contrast evaluation of an object image formed on the imaging element 106, based on an image blur correction amount for correcting the image blur.

Description

  The present invention relates to an imaging apparatus having an image blur correction function for suppressing image blur at the time of shooting and an autofocus function for a plurality of subjects, and a control method thereof.

  2. Description of the Related Art In recent years, a usage form in which shooting is performed while observing a subject image formed on an image sensor such as a CMOS sensor in real time when shooting a still image or a moving image (so-called live view shooting) is becoming common. As a focus control method for a subject at the time of performing live view shooting, for example, a focus detection method using a phase difference detection method on an imaging plane in an image sensor is known (see Patent Document 1).

JP 2004-191629 A

  However, when the focus detection method described in Patent Document 1 is used for an imaging optical system that performs image blur correction at the time of photographing by decentering the correction lens group, the change in the light vignetting is caused by the eccentricity of the correction lens group. As a result, the focus detection accuracy is lowered.

  An object of the present invention is to provide an imaging apparatus capable of obtaining high focus detection accuracy even when an image blur correction function is used.

  An image pickup apparatus according to the present invention uses an image pickup unit that picks up an image of a subject and an electric signal output from a focus detection pixel included in an image pickup element that constitutes the image pickup unit to detect a focus on the subject. Focus detection means, second focus detection means different from the first focus detection means for detecting the focus on the subject, and image blur correction means for calculating an image blur correction amount for correcting image blur. And a selection means for selecting which of the first focus detection means and the second focus detection means to use based on the image blur correction amount calculated by the image blur correction means. .

  According to the present invention, in an imaging apparatus having a focus detection element for performing focus detection of an imaging optical system on the imaging element, high focus detection accuracy can be obtained even when a mechanism that performs image blur correction is used. it can.

1 is a block diagram showing a schematic configuration of a first digital camera according to an embodiment of the present invention. It is a block diagram which shows schematic structure of the 2nd digital camera which concerns on embodiment of this invention. FIG. 3 is a plan view illustrating an example of a pixel arrangement structure of an image sensor of the first digital camera of FIG. 1 and the second digital camera of FIG. 2. It is a top view which shows the pixel arrangement | sequence structure of another image pick-up element which can be used as an image pick-up element of the 1st digital camera of FIG. 1, and the 2nd digital camera of FIG. It is a top view which shows the pixel arrangement | sequence structure of another image pick-up element which can be used as an image pick-up element of the 1st digital camera of FIG. 1, and the 2nd digital camera of FIG. FIG. 3 is a diagram illustrating an outline of an imaging optical system that performs image blur correction by decentering a second lens group in the first digital camera of FIG. 1 and an image sensor in the second digital camera of FIG. 2 in an optical format. is there. FIG. 4 is a diagram illustrating a relationship of a pupil projection image of a focus detection pixel with respect to an exit pupil of the imaging optical system when the focus detection pixel has the configuration of FIG. 3. FIG. 6 is a diagram illustrating a relationship of a pupil projection image of a focus detection pixel with respect to an exit pupil of the imaging optical system when the focus detection pixel has the configuration illustrated in FIG. 4 or FIG. 5. It is a figure which shows the output waveform of the focus detection pixel of A image and B image in the state of FIG.7 and FIG.8. It is a flowchart of the focus detection process in the digital camera of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, a digital camera such as a digital single-lens reflex camera or a compact digital camera is taken up as the imaging apparatus according to the present embodiment.

  FIG. 1 is a block diagram showing a schematic configuration of a first digital camera 100A according to an embodiment of the present invention. In the digital camera 100A, a camera body including the image sensor 106 and an imaging optical system are integrated or connected to be able to shoot a moving image and a still image. It has a camera shake correction mechanism for correcting the above.

  The digital camera 100 </ b> A includes a first lens group 101, an aperture 102, a second lens group 103, a third lens group 104, and an optical low-pass filter 105 that constitute an imaging optical system (imaging optical system). The digital camera 100 </ b> A includes an image sensor 106, a zoom actuator 111, a diaphragm actuator 112, a correction lens actuator 113, a focus actuator 114, a wireless communication unit 115, and an attitude detection unit 116.

  The first lens group 101 is a lens group disposed at the tip of the imaging optical system, and is movable in the optical axis direction. The diaphragm 102 adjusts the light amount at the time of shooting by adjusting the aperture diameter, and also has a function as an exposure time adjusting shutter at the time of still image shooting. The second lens group 103 is a correction lens group that corrects image blur at the time of hand-held shooting by performing an eccentric movement of the imaging optical system. Also, a zoom function that changes the focal length by changing the distance between the first lens group 101 and the second lens group 103 can be obtained. The third lens group 104 performs focus adjustment by movement in the optical axis direction. The optical low-pass filter 105 is an optical element for reducing false colors and moire in the captured image.

  In this embodiment, the image sensor 106 includes a CMOS sensor and its peripheral circuits. The CMOS sensor has a structure in which M pixels in the horizontal direction and N pixels (M and N are integers) in the vertical direction are squarely arranged. For example, a Bayer array primary color mosaic filter is formed on-chip. 2D single plate color sensor. The zoom actuator 111 rotates the cam cylinder (not shown) that houses the various lens groups described above to drive the various lens groups in the optical axis direction to perform zoom operations. Any one may be used.

  The aperture actuator 112 controls the aperture diameter of the aperture 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. The correction lens actuator 113 corrects the image blur of the subject image formed on the image sensor 106 by moving the second lens group 103 eccentrically in a direction orthogonal to the optical axis, for example. For example, the correction lens actuator 113 moves the second lens group 103 in two orthogonal directions in a plane orthogonal to the optical axis, and the image blur direction with respect to the image sensor 106 in the amount and direction of movement to be combined. Respond to changes. The focus actuator 114 performs focus adjustment by driving the third lens group 104 in the optical axis direction.

  The wireless communication unit 115 includes an antenna and a signal processing circuit for communicating with a server computer (not shown) through a network such as the Internet. The posture detection unit 116 is an electronic level for determining the shooting posture of the camera body, that is, whether it is horizontal position shooting or vertical position shooting.

  The digital camera 100A includes a CPU 121, a communication control circuit 122, an attitude detection circuit 123, an image sensor driving circuit 124, an image processing circuit 125, a focus driving circuit 126, and a correction lens driving circuit 127. The digital camera 100A also includes an aperture driving circuit 128, a zoom driving circuit 129, a display 131, an operation switch 132, and a flash memory 133.

  The CPU 121 includes a calculation unit that performs various controls of the camera body, a ROM, a RAM, an A / D converter, a D / A converter, a communication interface circuit, and the like. The CPU 121 drives various circuits included in the digital camera 100A based on a predetermined program stored in the ROM, and executes a series of operations such as focus detection, photographing, image processing, and image recording. The CPU 121 performs a focus detection process, a focus determination process, and a focus drive control process, which will be described later. The communication control circuit 122 transmits a captured image from the camera body to the server computer via the wireless communication unit 115, and receives images and various information from the server computer.

  The posture detection circuit 123 determines the posture of the camera body from the output signal of the posture detection unit 116. The image sensor drive circuit 124 controls the imaging operation of the image sensor 106, A / D converts the image signal acquired from the image sensor 106, and transmits the image signal to the CPU 121. The image processing circuit 125 performs processes such as γ conversion, color interpolation, and image compression of the image acquired by the image sensor 106. The focus drive circuit 126 drives and controls the focus actuator 114 based on the focus detection result, and drives the third lens group 103 in the optical axis direction to perform focus adjustment (focusing operation). The correction lens drive circuit 127 drives and controls the correction lens actuator 113 based on a signal output from a blur amount detection unit (not shown), and controls the eccentric movement of the second lens group 103 that is a correction lens group that corrects image blur. I do.

  The aperture driving circuit 128 controls the aperture of the aperture 102 by drivingly controlling the aperture actuator 112. The zoom drive circuit 129 drives the zoom actuator 111 according to the zoom operation of the photographer. The display 131 is a liquid crystal display (LCD) or the like, and includes information related to the shooting mode of the digital camera 100A, a preview image at the time of shooting, a confirmation image after shooting, a focus state display image at the time of focus detection, and the posture of the camera body. Display information. The operation switch 132 includes a power switch, a shooting start switch, a zoom operation switch, a shooting mode selection switch, and the like. The flash memory 133 is detachable from the camera body and stores captured images.

  FIG. 2 is a block diagram showing a schematic configuration of the second digital camera 100B according to the embodiment of the present invention. Compared with the first digital camera 100A shown in FIG. 1, the digital camera 100B includes an image sensor actuator 117 that drives the image sensor 106 instead of the correction lens actuator 113 that drives the second lens group 103. It is different in point. The digital camera 100B is different in that it includes an image sensor actuator drive circuit 130 that drives the image sensor actuator 117 instead of the correction lens drive circuit 127 that drives the correction lens actuator 113 provided in the digital camera 100A.

  However, the digital cameras 100 </ b> A and 100 </ b> B are common in that image blur correction is performed by moving the imaging optical system and the imaging element 106 to change the imaging position of the subject image. That is, in the digital camera 100B, the image blur correction of the subject image formed on the image sensor 106 is performed by moving the image sensor 106 eccentrically within a plane orthogonal to the optical axis.

  The image sensor actuator drive circuit 130 performs drive control of the image sensor actuator 117 based on a signal output from a blur amount detection unit (not shown), and performs eccentric movement control of the image sensor 106. The image sensor actuator 117, for example, moves the image sensor 106 in two orthogonal directions within a plane orthogonal to the optical axis, and responds to a change in the image blur direction relative to the image sensor 106 in the amount and direction of movement to be combined. I do.

  A focus detection method based on phase difference detection according to this embodiment will be described in comparison with a conventional focus detection method based on phase difference detection. Note that the focus detection method by phase difference detection according to the present embodiment is commonly used in the digital cameras 100A and 100B according to the above description.

  Conventionally, for example, as described in Japanese Patent Application Laid-Open No. 2-19813, phase difference detection is performed by deflecting some light beams of an imaging optical system to a focus detection optical system in order to detect a phase difference. Is going. In the focus detection optical system, each pair of two optical systems captures a partial light beam in the exit pupil range of the imaging optical system and forms an image on the pair of photoelectric conversion elements. Then, two formed images (hereinafter referred to as “A image” and “B image”) obtained by converting two optical images formed by the two optical systems for focus detection into electric signals by photoelectric conversion are shown. A phase difference that is a relative positional relationship is detected. Here, the relationship between the amount of change in the phase difference between the A image and the B image with respect to the shift (defocus) of the imaging position is determined by the configuration of the focus detection optical system. Can be requested. Therefore, the focal position of the subject image formed on the image sensor can be detected from the phase difference between the A image and the B image.

  The base line length K is expressed as “K = L / DEF”, where “L” is the distance (image shift amount) between the A image and B image to be correlated and the defocus amount is “DEF”. In calculating the baseline length K, it is necessary to know the optical characteristics and electrical characteristics of the imaging optical system and the focus detection pixel. Specifically, ray vignetting information for deriving the exit pupil shape of the imaging optical system, the relationship between the pupil image of the focus detection pixel projected at that position, and the light reception angle when the focus detection pixel receives light from the exit pupil Intensity distribution information is required.

  A conventional phase detection optical system for focus detection uses a light-shielding mask to separate the light transmission range of the imaging optical system (pupil separation), and light in the light-shielding range does not cause vignetting during focus detection. As described above, it is assumed that the imaging optical system is in an open state and the brightness (effective F number) exceeds a certain level. In this case, since the baseline length information necessary for focus position detection does not fluctuate, the baseline length information unique to the focus detection optical system may be stored in the imaging apparatus.

  However, many recent digital single-lens reflex cameras have a so-called live view shooting function in which a subject image formed on an image sensor is photographed while being observed in real time with a liquid crystal display device or an electronic viewfinder. . In order to obtain an in-focus state while making use of this function, a technique has been proposed in which an imaging pixel on an imaging element is used as a phase difference type focus detection pixel. In this embodiment, such a focus detection method is used, and the configuration and light receiving characteristics of the focus detection pixel will be described below.

  FIG. 3 is a plan view showing an example of a pixel arrangement structure of the image sensor 106 in the digital cameras 100A and 100B. The vertical direction in FIG. 3 is the Y direction, and the horizontal direction is the X direction. The image sensor 106 includes pixel groups 300, 301, 302, 303, and 304. The pixel group 300 is a pixel for forming a captured image, and the pixel groups 301 to 304 are focus detection pixel groups in which a light shielding structure is provided in the pixels. Note that the pixel groups 301 to 304 are equivalent to the known technique described in, for example, Japanese Patent Application Laid-Open No. 2009-244862.

  In FIG. 3, pixel groups 301 and 302 arranged in a line in the Y direction have horizontal stripe pattern shapes using a photoelectric conversion signal waveform of a subject image in the Y direction as a pair of correlation calculation electric signals for phase difference detection. The focus position of the subject is detected. Similarly, in FIG. 3, pixel groups 303 and 304 arranged in a line in the X direction are used as a pair of correlation calculation electric signals for detecting a photoelectric conversion signal waveform phase difference of the subject image in the X direction. This is for detecting the focus position of a subject having a vertical stripe pattern shape.

  FIG. 4 is a plan view showing a pixel arrangement structure of an image sensor in which two photoelectric conversion units are arranged for one microlens, and such an image sensor is used as the image sensor 106 of the digital cameras 100A and 100B. You can also The vertical direction in FIG. 4 is the Y direction, and the horizontal direction is the X direction. In FIG. 4, the pixel group 400 arranged in the X direction is for detecting the focal position of the subject in the stripe pattern in the Y direction using each electric signal from the pixels 402 and 403 as a pair of correlation calculation electric signals. It is. In FIG. 4, the pixel group 401 arranged in the Y direction detects the focal position of the subject in the X-direction stripe pattern using each electrical signal from the pixels 404 and 405 as a pair of correlation calculation electrical signals. Is. Note that the electrical signals of the pixels 402 and 403 and the electrical signals of the pixels 404 and 405 can be added to be used as a captured image signal.

  FIG. 5 is a plan view showing a pixel arrangement structure of an image sensor in which four photoelectric conversion units are arranged for one microlens. This image sensor may be used as the image sensor 106 of the digital cameras 100A and 100B. it can. The vertical direction in FIG. 5 is the Y direction, and the horizontal direction is the X direction. In the image sensor of FIG. 5, the pixel characteristics similar to those of the image sensor described with reference to FIG. 3 can be obtained by changing the addition method of the electric signals of the four photoelectric conversion units. That is, the pixel group 500 is obtained by adding the respective photoelectric conversion signals of the pixels 501 and 502 and the pixels 503 and 504 arranged in the X direction when performing focus detection of a subject having a stripe pattern in the Y direction. Two rows of electric signal waveforms are used as a pair of correlation calculation electric signals. Further, the pixel group 500 is obtained by adding the photoelectric conversion signals of the pixels 501 and 503 and the pixels 502 and 504 arranged in the Y direction when performing focus detection of a subject having a stripe pattern in the X direction. The two rows of electric signal waveforms are used as a pair of correlation calculation electric signals.

  Note that the two methods of adding photoelectric conversion signals for focus detection can be performed by dividing the imaging surface of the image sensor into a plurality of blocks and changing the pixel addition method for each block, or by staggered arrangement. For example, the pixel addition method may be changed alternately. In this case, since the vertical stripe pattern and horizontal stripe pattern subjects can be evaluated simultaneously, the subject pattern direction dependency can be eliminated during focus detection.

  Further, the photoelectric conversion signal addition method for focus detection may be switched in all pixels according to the photographing state or in time series. In this case, since the focus detection pixels for detecting the focus of the subject in the same pattern direction are in a dense state, the subject having a thin line segment generated when the focus detection pixels are sparse cannot be detected in the vicinity of the in-focus state. Can be avoided.

  On the other hand, by adding the electrical signals output from the pixels 501 to 504, they can be used as a captured image signal. When such an image pickup device structure is used, it is not necessary to branch a part of the subject image from the image pickup optical system to the focus detection optical system unlike the conventional phase difference detection method. Therefore, live view shooting can be performed while monitoring the subject image for which the image sensor receives light and records the image in real time, and the focus of the phase difference detection method that cannot be achieved without the subject beam splitting mechanism in conventional movie shooting. Detection is possible.

  However, in the above live view shooting, in order to perform image recording in real time, it is necessary to change the aperture value of the imaging optical system in accordance with the change in the brightness of the subject image. Therefore, the imaging optical system cannot always be kept open for focus detection as in the conventional phase difference detection method described above.

  The problem in this case is that if the effective F-number of the imaging optical system becomes larger (becomes darker) due to the diaphragm aperture operation at the time of shooting, the exit pupil range of the imaging optical system becomes smaller. This is the occurrence of vignetting in the light beam captured for detection. As a result, a change occurs in an electrical signal (hereinafter referred to as an “image signal”) captured for focus detection, and the relationship between the defocus amount and the change amount of the phase difference of the image signal (K = L / DEF). At the same time, an error occurs when performing correlation calculation on the image signal. Also, when performing focus detection with focus detection pixels having a peripheral image height at which the aperture efficiency of the imaging optical system is reduced, light vignetting occurs and the same problem occurs. In order to solve this problem, for example, Japanese Patent Application Laid-Open No. 2004-191629 proposes a method of acquiring light vignetting information of an imaging optical system at the time of focus detection and correcting an image signal for focus detection. .

  However, many recent photographing lenses having an image stabilization function correct image blur by moving the correction lens group constituting the imaging optical system eccentrically. In this case, the light vignetting state changes during the eccentric movement. Therefore, the focus detection accuracy is affected. On the other hand, there is also a method of performing image blur correction by moving the image sensor so as to follow the image blur direction. However, in this method, the light beam emitted to a certain area of the image pickup device moves the image pickup device, so that the apparent emission angle from the image pickup optical system always changes (the image height changes). In other words, the vignetting state also changes.

  FIG. 6 shows an outline of the imaging optical system of FIG. 1 or FIG. 2 according to the present embodiment in which the second lens group 103, which is a correction lens group, or the image sensor 106 performs image blur correction by performing an eccentric movement in an optical format. FIG. In FIG. 6, it is assumed that the first lens group 101 located on the subject side has a positive refractive power. The second lens group 103 has a negative refracting power, and performs an eccentric movement in a direction perpendicular to the optical axis to generate an imaging position displacement action, thereby correcting (cancelling) image blur. The third lens group 104 has a positive refractive power. The diaphragm 102, the optical low-pass filter 105, and the image sensor 106 shown in FIG. 6 are based on the description with reference to FIG. In FIG. 6, the center beam of the screen is “L0” and the peripheral beam is “L1”.

  FIG. 6A shows a state before image blur correction is performed. FIG. 6B shows a state in which the second lens group 103 is moved eccentrically in order to obtain an image blur correction function corresponding to the angle Δω as the amount of change in the angle of view. In the state of FIG. 6B, the effective range of the light beam of the second lens group 103 enters the pupil range of the imaging optical system at the position of the stop 102 due to the eccentricity of the second lens group 103, and as a result, asymmetrical. Light vignetting has occurred. FIG. 6C shows a state in which the image sensor 106 is moved eccentrically and image blur correction is performed, and an image blur correction action corresponding to the angle Δω is obtained as in FIG. 6B. . In the state shown in FIG. 6C, the center of the image sensor 106 apparently changes to a state where the center of the image sensor 106 has moved to the peripheral image height as viewed from the imaging optical system, and the light vignetting that occurs as the image height increases. Has occurred.

  The influence on the baseline length of the light vignetting that occurs when the second lens group 103 or the image sensor 106 in the image pickup optical system shown in FIG. 6 is decentered when performing focus detection on the subject at the center of the image sensor 106. Will be described below with reference to FIGS. In the following description with reference to FIGS. 7 and 8, the imaging optical system is assumed to have a circular aperture.

  FIG. 7 is a diagram showing the relationship of the pupil projection image of the focus detection pixel with respect to the exit pupil of the imaging optical system when the focus detection pixel has the configuration shown in FIG. FIG. 7A shows a state where the second lens group 103 or the image sensor 106 is in an undecentered state, and corresponds to FIG. FIG. 7B shows a state in which the second lens group 103 or the image sensor 106 is slightly decentered. FIG. 7C shows a state in which the second lens group 103 or the image sensor 106 is moved greatly decentered. In FIG. 7, the focus detection pixel 700 for the A image, the focus detection pixel 704 for the B image, the microlens 701, the light shielding member 702, and the photoelectric conversion unit 703 are illustrated as components of the image sensor 106.

  In FIG. 7, “EP0” and “EPO ′” indicate the exit pupil of the imaging optical system in the absence of light vignetting. “EP1” is the exit pupil of the imaging optical system when the second lens group 103 or the image sensor 106 decenters and causes vignetting during the image blur correction shown in FIGS. 6B and 6C. Show. “EPa0” and “EPb0” respectively indicate the pupil projection images of the focus detection pixels for the A image and the B image, and “EPa1” and “EPb1” respectively indicate when the second lens group 103 is moved eccentrically. The pupil projection image of the focus detection pixel for A image and B image in which the effective range was narrowed is shown. As described with reference to FIG. 3, such focus detection pixels are arranged in a line direction, interpolate photoelectric conversion signals of the respective focus detection pixels, and perform an electric signal waveform for performing a pair of correlation operations described below. Make it.

  FIG. 8 is a diagram showing the relationship of the pupil projection image of the focus detection pixel with respect to the exit pupil of the imaging optical system when the focus detection pixel has the configuration shown in FIG. 4 or FIG. An image sensor 800 shown in FIG. 8 includes two photoelectric conversion units 802 and 803 that receive light through one microlens 801 and perform photoelectric conversion for forming an A image and a B image, respectively. Since the photoelectric conversion units 802 and 803 each receive a light beam that has passed through an effective range outside the optical axis of the microlens 801, the photoelectric conversion units 802 and 803 receive transmitted light beams in different regions on the exit pupil of the imaging optical system. As a result, it is possible to obtain a pupil-separated ray necessary for focus detection by the phase difference detection method.

  FIG. 8A shows a state where the second lens group 103 or the image sensor 106 is in an undecentered state, and corresponds to FIG. FIG. 8B shows a state in which the second lens group 103 or the image sensor 106 is slightly decentered. FIG. 8C shows a state in which the second lens group 103 or the image sensor 106 is greatly decentered.

  8 has the structure of the pixel group 500 shown in FIG. 5 and the photoelectric conversion units 802 and 803 correspond to the photoelectric conversion units of the pixels 503 and 504, the pixels 501, Each photoelectric conversion unit 502 exists in the depth direction overlapping with the photoelectric conversion units 802 and 803. In this case, the addition of the electric signals output from the pixels 501 and 503 and the addition of the electric signals output from the pixels 502 and 504 may be respectively performed and used as a pair of electric signals for focus detection.

  FIG. 9A shows an A image in the state shown in FIGS. 7A and 8A (the second lens group 103 or the image sensor 106 is in an undecentered state and no light vignetting occurs). It is a figure which shows the output waveform of the focus detection pixel of B image. FIG. 9B shows an A image and a B image in the state of FIGS. 7B and 8B (the state in which the second lens group 103 or the image sensor 106 is slightly decentered). It is a figure which shows the output waveform of a focus detection pixel.

  The electrical signal waveforms AI0 and BI0 shown in FIG. 9A are obtained by interpolating and synthesizing electrical signals output from the focus detection pixel groups for the A image and the B image, respectively. L0 is indicated by the distance between the peaks of the electric signal waveforms AI0 and BI0.

  Similarly, electrical signal waveforms AI1 and BI1 shown in FIG. 9B are obtained by interpolating electrical signals output from the focus detection pixel groups for the A and B images, respectively. In FIG. 9B, as shown in FIG. 7B and FIG. 8B, a state in which light vignetting occurs in the pupil of the focus detection pixel for B image (changes in the optical axis direction of the imaging optical system). Therefore, the electric signal waveform AI1 and the electric signal waveform BI1 are asymmetrical. On the other hand, since no light vignetting occurs in the pupil of the focus detection pixel for the A image, the electric signal waveform AI1 is equivalent to the electric signal waveform AI0. The distance L1 between the gravity center positions of the signal strengths of the electric signal waveforms AI1 and BI1 is shorter than the distance L0 between the gravity center positions of the signal strengths of the electric signal waveforms AI0 and BI0 in FIG.

  Therefore, in the state of FIG. 9B, compared to the state of FIG. 9A, there is a change that the base line length is shortened due to the influence of light vignetting due to the eccentric movement of the second lens group 103 or the image sensor 106. . For this reason, if the amount of decentering movement of the second lens group 103 or the image sensor 106 exceeds the specified amount in order to perform image blur correction, the focus detection accuracy of the above-described phase difference detection method decreases.

  Therefore, in this embodiment, the focus detection method is switched when it is determined that the focus detection accuracy is hindered, and the specific processing contents will be described below with reference to the flowchart of FIG. FIG. 10 is a flowchart of focus detection processing in the digital camera 100A. The various processes shown in FIG. 10 are realized by the CPU 121 reading a predetermined program from the ROM, developing and executing it in the work area of the RAM, and driving various circuits and actuators.

  First, when the photographer turns on the power switch of the digital camera 100A, the CPU 121 checks the operation of various actuators and the image sensor 106, initializes the memory contents and the execution program, and executes the shooting preparation operation (Start). ). When the photographer operates the shutter button, the defocus amount is obtained by the phase difference detection method (first focus detection method) in steps S101 to S104.

  First, in step S101, the CPU 121 starts image blur correction by decentering movement of the second lens group 103 which is a correction lens group constituting the imaging optical system. Simultaneously with step S101, in step S102, the CPU 121 starts AF signal processing (signal processing for automatic focus detection), that is, an autofocus operation.

  Specifically, in the image blur correction in step S101, the CPU 121 performs an image blur correction amount detection process based on an output signal from the attitude detection unit 116 or the like. Further, in the AF signal processing in step S102, the CPU 121 performs an interpolation process for converting an electric signal output by photoelectric conversion of a light beam incident on the focus detection pixel into a signal waveform for correlation calculation, and if necessary. Signal correction processing. In the case of the digital camera 100B, instead of the eccentric movement of the second lens group 103, the focus detection operation is started simultaneously with the start of image blur correction by performing the eccentric movement of the image sensor 106.

  Next, in step S103 after step S102, the CPU 121 performs phase difference correlation calculation (correlation calculation of a pair of image signals) to calculate an image shift amount. In step S104, the CPU 121 calculates the defocus amount from the relationship between the image shift amount obtained in step S103 and the baseline length calculated in advance.

  Thereafter, in step S105, the CPU 121 selects whether to use a focus detection method based on a phase difference detection method or a focus detection method based on contrast evaluation. Specifically, in step S105, the CPU 121 determines whether the image blur correction amount obtained in step S101 exceeds a predetermined threshold value set in advance. In the process of step S105, the image signal obtained in step S102 does not cause an optical vignetting due to image blur correction to cause a correlation calculation error, or an error in the baseline length for calculating the defocus amount. This is a process for determining whether or not a problem has occurred by setting a threshold value.

  If the image blur correction amount does not exceed the threshold (NO in S105), the CPU 121 determines that the defocus amount obtained in step S104 is reliable, and advances the process to step S106. On the other hand, if the image blur correction amount exceeds the threshold value (YES in S105), the CPU 121 determines that the defocus amount obtained in step S104 is not reliable, and determines the focus detection method based on contrast evaluation (second detection). The process proceeds to step S107.

  In step S106, the CPU 121 performs in-focus determination based on the defocus amount obtained by the phase difference detection method obtained in step S104. If the CPU 121 determines that the in-focus state is achieved (YES in S106), the CPU 121 ends the process, and thereby the exposure process is performed. On the other hand, if the CPU 121 determines that it is not in focus (NO in S106), the process proceeds to step S110. In step S110, the CPU 121 corrects the defocus amount calculated in step S104 to obtain a focus amount for achieving a focused state, and drives the third lens group 104, which is a focus lens, in the optical axis direction. Thereafter, the CPU 121 returns the process to step S101 and repeats the process of calculating the defocus amount and determining the in-focus state again.

  In step S107, the CPU 121 finely drives the third lens group 104, which is a focus lens, in order to perform focus detection by contrast evaluation. That is, step S107 is a process of correcting the out-of-focus by detecting the out-of-focus direction (whether the subject is out of focus or the image plane is out of focus) from the defocus amount obtained in step S104. . In subsequent step S108, the CPU 121 evaluates the contrast value at an arbitrary spatial frequency of the subject image to be evaluated for focus. In subsequent step S109, the CPU 121 performs focus determination from the contrast value of the subject evaluated in step S108. In this in-focus determination, it may be determined that the in-focus state is achieved when the contrast value of the subject becomes a value greater than or equal to a specified value.

  If the CPU 121 determines that the in-focus state is achieved (YES in S109), the CPU 121 ends the process, and thereby the exposure process is performed. On the other hand, if the CPU 121 determines that it is not in focus (NO in S109), the process returns to step S101. When the focus detection method is changed to the contrast evaluation, the focus position detection (of the so-called hill-climbing method) for deriving the peak position of the contrast value from the relationship between the focus lens position and the contrast value is performed in step S102 or step S107. From step S109 to step S109.

  As described above, according to the present embodiment, in an imaging device including an imaging device that performs phase difference detection type focus detection, high-speed detection is performed while maintaining high focus detection accuracy when the image blur correction mechanism is used. A focusing operation can be realized.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of this invention, and it is also possible to combine each embodiment suitably. For example, in the above embodiment, the phase difference detection method and the contrast evaluation method are used as the focus detection method. However, the present invention is not limited to this. Instead of the contrast evaluation method, a triangular distance measurement method using an external distance measurement unit, an active method using infrared light projecting and receiving, or an external passive distance measurement method, etc. May be used. Further, the present invention is not limited to a digital camera, and can be applied to various electronic devices such as a digital video camera and a mobile phone or a portable game machine having a photographing function using an image sensor.

101 First lens group 102 Aperture mechanism 103 Second lens group (correction lens group)
104 Third lens group (focus lens)
106 Image Sensor 113 Correction Lens Actuator 114 Focus Actuator 116 Posture Detection Unit 117 Image Sensor Actuator 121 CPU
123 posture detection circuit 126 focus drive circuit 127 correction lens drive circuit 130 imaging element actuator drive circuit

Claims (6)

Imaging means for imaging a subject;
First focus detection means for detecting a focus on the subject using an electrical signal output from a focus detection pixel included in an image sensor included in the imaging means;
Second focus detection means different from the first focus detection means for detecting a focus on the subject;
Image blur correction means for calculating an image blur correction amount for correcting image blur;
An imaging apparatus comprising: a selection unit that selects which of the first focus detection unit and the second focus detection unit to use based on an image blur correction amount calculated by the image blur correction unit. .   The imaging apparatus according to claim 1, wherein the second focus detection unit detects a focus position by evaluating a contrast of a subject image formed on the imaging element.   The second focus detection unit detects the out-of-focus direction from the defocus amount obtained by the first focus detection unit, and drives the focus lens included in the imaging optical system of the imaging unit to defocus. The imaging apparatus according to claim 2, wherein correction is performed.   4. The imaging apparatus according to claim 1, wherein the image blur correction unit corrects image blur by decentering a correction lens group included in an imaging optical system of the imaging unit. 5. .   4. The image pickup apparatus according to claim 1, wherein the image blur correction unit corrects the image blur by moving the image pickup device eccentrically. 5. A method for controlling an imaging apparatus having imaging means for imaging a subject,
A first focus detection step of detecting a focus on the subject using an electrical signal output from a focus detection pixel included in an image sensor that constitutes the imaging means;
A second focus detection step for detecting a focus on the subject in a manner different from the first focus detection step;
An image blur correction step for calculating an image blur correction amount for correcting the image blur; and
An imaging method comprising: a selection step for selecting which of the first focus detection step and the second focus detection step to use based on the image blur correction amount calculated in the image blur correction step. Control method of the device.

Images