JP2013011783A - Focus detection device and imaging apparatus - Google Patents

Abstract

A focus detection apparatus capable of detecting a focus state of an optical system satisfactorily.
An imaging unit having an imaging pixel that outputs an image signal corresponding to an image by an optical system, a pair of focus detection pixel rows that receive a pair of light beams, and a pair of focus detection pixel rows. While the output first data string and second data string are relatively shifted in a one-dimensional manner, the correlation amount between the first data string and the second data string is calculated, and the extreme value of the correlation amount is calculated. By detecting the shift amount obtained, the phase difference detection unit 21 that detects the focus state of the optical system, the diaphragm 34 that limits the light beam incident on the imaging unit, and the aperture of the correlation amount based on the aperture value by the diaphragm. A shift calculation range in which the first data string and the second data string are relatively shifted when detecting the shift amount from which the value is obtained is determined as the first shift calculation range, and the phase difference is determined in the first shift calculation range. Calculate the amount of correlation in the detector Focus detection device, characterized in that it comprises a control unit 21, a to.
[Selection] Figure 1

Description

  The present invention relates to a focus detection apparatus and an imaging apparatus.

  Conventionally, the imaging device includes a pair of focus detection pixel rows, and the first data row and the second data row output from the pair of focus detection pixel rows are relatively shifted. A focus detection device is known that calculates a defocus amount based on a shift amount by which a correlation amount with a second data string is calculated and an extreme value of the correlation amount is obtained (for example, Patent Document 1).

JP 2011-90143 A

  However, in the related art, since the imaging element includes a focus detection pixel, the distance detection pupil of the focus detection pixel may be larger than the exit pupil, and even when the defocus amount is the same, depending on the aperture value In some cases, the amount of shift between the first data row and the second data row output from the pair of focus detection pixel rows is greatly different. Therefore, depending on the aperture value, the shift range for shifting the first data string and the second data string becomes too small with respect to the shift amount between the first data string and the second data string, and the defocus amount is reduced. When it is impossible to calculate, or conversely, the shift range becomes too large with respect to the shift amount between the first data string and the second data string, and the time required to calculate the defocus amount becomes long. was there.

  The problem to be solved by the present invention is to provide a focus detection device that can detect the focus state of an optical system satisfactorily.

  The present invention solves the above problems by the following means. In the following description, reference numerals corresponding to the drawings showing the embodiment of the present invention are given and described. However, the reference numerals are only for facilitating the understanding of the invention and are not intended to limit the invention. .

  [1] A focus detection apparatus according to the present invention captures an image by an optical system and outputs an image signal corresponding to the captured image (221), and a pair that receives a pair of pupil-divided light beams. An imaging unit (22) having a plurality of focus detection pixel rows (22a, 22b, 22c), and a first data row and a second data row respectively output from the pair of focus detection pixel rows are arranged in a one-dimensional manner. And calculating a correlation amount between the first data string and the second data string, and detecting a shift amount at which an extreme value of the correlation amount is obtained. Based on the phase difference detection unit (21) for detecting the focus state, the diaphragm (34) for limiting the light beam that passes through the optical system and is incident on the imaging unit, and the aperture value by the diaphragm, the correlation amount When detecting the shift amount that can obtain the extreme value, A shift calculation range for relatively shifting the first data string and the second data string is determined as a first shift calculation range, and the phase difference detection unit calculates the correlation amount in the first shift calculation range. And a control unit (21) for performing the above.

  [2] In the invention related to the focus detection apparatus, the control unit (21) can be configured to make the first shift calculation range smaller as the aperture value by the aperture (34) is larger. .

  [3] In the invention related to the focus detection device, an evaluation value related to the contrast of the image by the optical system is calculated based on the image signal output from the imaging pixel (221), thereby A contrast detection unit (21) for detecting the focus state can be further provided.

  [4] In the invention related to the focus detection apparatus, the control unit (21) detects a shift amount that can obtain the extreme value of the correlation amount, and the reliability of the calculation result of the correlation amount is predetermined. A second shift calculation range that is narrower than the first shift calculation range is determined based on the shift amount from which the detected extreme value of the correlation amount is obtained, and the second shift calculation range The phase difference detector (21) can be configured to calculate the correlation amount.

  [5] In the invention related to the focus detection device, the control unit (21) drives the focus adjustment lens (32) to the in-focus position based on the shift amount that can obtain the extreme value of the correlation amount. And determining whether or not the shift amount for obtaining the extreme value of the correlation amount is detected and the reliability of the calculation result of the correlation amount is equal to or greater than a predetermined value, and based on the determination result In the second shift calculation range, it can be configured to determine whether or not to cause the phase difference detection unit (21) to calculate the correlation amount.

  [6] An imaging apparatus according to the present invention includes the focus detection apparatus.

  According to the present invention, the focus state of the optical system can be detected satisfactorily.

FIG. 1 is a block diagram showing a camera according to the present embodiment. FIG. 2 is a front view showing a focus detection position on the imaging surface of the imaging device shown in FIG. FIG. 3 is a front view schematically showing the arrangement of the focus detection pixels 222a and 222b by enlarging the III part of FIG. FIG. 4 is an enlarged front view showing one of the imaging pixels 221. FIG. 5A is an enlarged front view showing one of the focus detection pixels 222a, and FIG. 5B is an enlarged front view showing one of the focus detection pixels 222b. FIG. 6 is an enlarged cross-sectional view showing one of the imaging pixels 221. FIG. 7A is an enlarged cross-sectional view showing one of the focus detection pixels 222a, and FIG. 7B is an enlarged cross-sectional view showing one of the focus detection pixels 222b. 8 is a cross-sectional view taken along line VIII-VIII in FIG. FIG. 9 is a flowchart showing the operation of the camera according to the present embodiment. FIG. 10A is a diagram showing an example of the relationship between the exit pupil and the distance measurement pupil of the focus detection pixel when the aperture value is F2.8, and FIG. 8 is a graph showing an example of signal strengths of a first data string and a second data string when the number is 8. FIG. FIG. 11A is a diagram showing an example of the relationship between the exit pupil and the distance measurement pupil of the focus detection pixel when the aperture value is F5.6, and FIG. 6 is a graph showing an example of signal intensities of a first data string and a second data string in the case of 6. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a main part configuration diagram showing a digital camera 1 according to an embodiment of the present invention. A digital camera 1 according to the present embodiment (hereinafter simply referred to as a camera 1) includes a camera body 2 and a lens barrel 3, and the camera body 2 and the lens barrel 3 are detachably coupled by a mount unit 4. Yes.

  The lens barrel 3 is an interchangeable lens that can be attached to and detached from the camera body 2. As shown in FIG. 1, the lens barrel 3 includes a photographic optical system including lenses 31, 32, 33 and a diaphragm 34.

  The lens 32 is a focus lens, and can adjust the focal length of the photographing optical system by moving in the direction of the optical axis L1. The focus lens 32 is provided so as to be movable along the optical axis L1 of the lens barrel 3, and its position is adjusted by the focus lens drive motor 36 while its position is detected by the encoder 35.

  The specific configuration of the moving mechanism along the optical axis L1 of the focus lens 32 is not particularly limited. For example, a rotating cylinder is rotatably inserted into a fixed cylinder fixed to the lens barrel 3, a helicoid groove (spiral groove) is formed on the inner peripheral surface of the rotating cylinder, and the focus lens 32 is fixed. The end of the lens frame is fitted into the helicoid groove. Then, by rotating the rotating cylinder by the focus lens drive motor 36, the focus lens 32 fixed to the lens frame moves straight along the optical axis L1.

  As described above, the focus lens 32 fixed to the lens frame by rotating the rotary cylinder with respect to the lens barrel 3 moves straight in the direction of the optical axis L1, but the focus lens drive motor 36 as the drive source is the lens. The lens barrel 3 is provided. The focus lens drive motor 36 and the rotary cylinder are connected by a transmission composed of a plurality of gears, for example, and when the drive shaft of the focus lens drive motor 36 is driven to rotate in any one direction, it is transmitted to the rotary cylinder at a predetermined gear ratio. Then, when the rotating cylinder rotates in any one direction, the focus lens 32 fixed to the lens frame moves linearly in any direction of the optical axis L1. When the drive shaft of the focus lens drive motor 36 is rotated in the reverse direction, the plurality of gears constituting the transmission also rotate in the reverse direction, and the focus lens 32 moves straight in the reverse direction of the optical axis L1. .

  The position of the focus lens 32 is detected by the encoder 35. As described above, the position of the focus lens 32 in the optical axis L1 direction correlates with the rotation angle of the rotating cylinder, and can be obtained by detecting the relative rotation angle of the rotating cylinder with respect to the lens barrel 3, for example.

  As the encoder 35 of this embodiment, an encoder that detects the rotation of a rotating disk coupled to the rotational drive of the rotating cylinder with an optical sensor such as a photo interrupter and outputs a pulse signal corresponding to the number of rotations, or a fixed cylinder And the contact point of the brush on the surface of the flexible printed wiring board provided on either one of the rotating cylinders, and the brush contact provided on the other, the amount of movement of the rotating cylinder (in either the rotational direction or the optical axis direction) A device that detects a change in the contact position according to the detection circuit using a detection circuit can be used.

  The focus lens 32 can move in the direction of the optical axis L1 from the end on the camera body side (also referred to as the closest end) to the end on the subject side (also referred to as the infinite end) by the rotation of the rotating cylinder described above. it can. Incidentally, the current position information of the focus lens 32 detected by the encoder 35 is sent to the camera control unit 21 to be described later via the lens control unit 37, and the focus lens drive motor 36 calculates the focus calculated based on this information. The driving position of the lens 32 is driven by being sent from the camera control unit 21 via the lens control unit 37.

  The diaphragm 34 is configured such that the aperture diameter around the optical axis L1 can be adjusted in order to limit the amount of light flux that passes through the photographing optical system and reaches the image sensor 22 and to adjust the blur amount. Adjustment of the aperture diameter by the diaphragm 34 is performed, for example, by sending the aperture diameter calculated in the automatic exposure mode from the camera control unit 21 via the lens control unit 37. Further, the aperture diameter corresponding to the set aperture value is input from the camera control unit 21 to the lens control unit 37 by a manual operation by the operation unit 28 provided in the camera body 2. The aperture diameter of the aperture 34 is detected by an aperture sensor (not shown), and the lens controller 37 recognizes the current aperture diameter.

  On the other hand, the camera body 2 is provided with an imaging element 22 that receives the light beam L1 from the photographing optical system on a planned focal plane of the photographing optical system, and a shutter 23 is provided on the front surface thereof. The image sensor 22 is composed of a device such as a CCD or CMOS, converts the received optical signal into an electrical signal, and sends it to the camera control unit 21. The captured image information sent to the camera control unit 21 is sequentially sent to the liquid crystal drive circuit 25 and displayed on the electronic viewfinder (EVF) 26 of the observation optical system, and a release button ( When (not shown) is fully pressed, the photographed image information is recorded in the memory 24 that is a recording medium. As the memory 24, any of a removable card type memory and a built-in type memory can be used. An infrared cut filter for cutting infrared light and an optical low-pass filter for preventing image aliasing noise are disposed in front of the imaging surface of the image sensor 22. Details of the structure of the image sensor 22 will be described later.

  The camera body 2 is provided with an observation optical system for observing an image picked up by the image pickup device 22. The observation optical system of the present embodiment includes an electronic viewfinder (EVF) 26 composed of a liquid crystal display element, a liquid crystal driving circuit 25 that drives the electronic viewfinder (EVF) 26, and an eyepiece lens 27. The liquid crystal drive circuit 25 reads the captured image information captured by the image sensor 22 and sent to the camera control unit 21, and drives the electronic viewfinder 26 based on the read image information. Thereby, the user can observe the current captured image through the eyepiece lens 27. Note that, instead of or in addition to the observation optical system using the optical axis L2, a liquid crystal display may be provided on the back surface of the camera body 2, and a photographed image may be displayed on the liquid crystal display.

  A camera control unit 21 is provided in the camera body 2. The camera control unit 21 is electrically connected to the lens control unit 37 through an electric signal contact unit 41 provided in the mount unit 4, receives lens information from the lens control unit 37, and defocuses to the lens control unit 37. Send information such as volume and aperture diameter. The camera control unit 21 reads out the pixel output from the image sensor 22 as described above, generates image information by performing predetermined information processing on the read out pixel output as necessary, and generates the generated image information. Is output to the liquid crystal driving circuit 25 and the memory 24 of the electronic viewfinder 26. The camera control unit 21 controls the entire camera 1 such as correction of image information from the image sensor 22 and detection of a focus adjustment state and an aperture adjustment state of the lens barrel 3.

  In addition to the above, the camera control unit 21 detects the focus state of the photographic optical system by the phase detection method and the focus state of the photographic optical system by the contrast detection method based on the pixel data read from the image sensor 22. I do. A specific focus state detection method will be described later.

  The operation unit 28 is a shutter release button or an input switch for the user to set various operation modes of the camera 1. Switching between the autofocus mode / manual focus mode and the one-shot mode / continuous mode is also possible in the autofocus mode. The as mode can be switched. Here, the one-shot mode is a mode in which the position of the focus lens 32 once adjusted is fixed and photographing is performed at the focus lens position, whereas the continuous mode is a mode in which the position of the focus lens 32 is fixed. In this mode, the focus lens position is adjusted according to the subject. Various modes set by the operation unit 28 are sent to the camera control unit 21, and the operation of the entire camera 1 is controlled by the camera control unit 21. The shutter release button includes a first switch SW1 that is turned on when the button is half-pressed and a second switch SW2 that is turned on when the button is fully pressed.

  Next, the image sensor 22 according to the present embodiment will be described.

  FIG. 2 is a front view showing the imaging surface of the image sensor 22, and FIG. 3 is a front view schematically showing the arrangement of the focus detection pixels 222a and 222b by enlarging the III part of FIG.

  As shown in FIG. 3, the imaging element 22 of the present embodiment includes a green pixel G having a color filter in which a plurality of imaging pixels 221 are two-dimensionally arranged on the plane of the imaging surface and transmit a green wavelength region. A red pixel R having a color filter that transmits a red wavelength region and a blue pixel B having a color filter that transmits a blue wavelength region are arranged in a so-called Bayer Arrangement. That is, in four adjacent pixel groups 223 (dense square lattice arrangement), two green pixels are arranged on one diagonal line, and one red pixel and one blue pixel are arranged on the other diagonal line. The image sensor 22 is configured by repeatedly arranging the pixel group 223 on the imaging surface of the image sensor 22 in a two-dimensional manner with the Bayer array pixel group 223 as a unit.

  The unit pixel group 223 may be arranged in a dense hexagonal lattice arrangement other than the dense square lattice shown in the figure. Further, the configuration and arrangement of the color filters are not limited to this, and an arrangement of complementary color filters (green: G, yellow: Ye, magenta: Mg, cyan: Cy) can also be adopted.

  FIG. 4 is an enlarged front view showing one of the imaging pixels 221, and FIG. 6 is a cross-sectional view. One imaging pixel 221 includes a micro lens 2211, a photoelectric conversion unit 2212, and a color filter (not shown), and a photoelectric conversion unit is formed on the surface of the semiconductor circuit substrate 2213 of the image sensor 22 as shown in the cross-sectional view of FIG. 2212 is built in and a microlens 2211 is formed on the surface. The photoelectric conversion unit 2212 is configured to receive an imaging light beam that passes through an exit pupil (for example, F1.0) of the photographing optical system by the micro lens 2211, and receives the imaging light beam.

  In addition, focus detection pixel rows 22a, 22b, and 22c in which focus detection pixels 222a and 222b are arranged in place of the above-described imaging pixels 221 at the center of the image pickup surface of the image pickup element 22 and three positions that are symmetrical from the center. Is provided. As shown in FIG. 3, one focus detection pixel column includes a plurality of focus detection pixels 222 a and 222 b that are alternately arranged adjacent to each other in a horizontal row (22 a, 22 c, 22 c). Yes. In the present embodiment, the focus detection pixels 222a and 222b are densely arranged without providing a gap at the position of the green pixel G and the blue pixel B of the image pickup pixel 221 arranged in the Bayer array.

  Note that the positions of the focus detection pixel rows 22a to 22c shown in FIG. 2 are not limited to the illustrated positions, and may be any one or two, or may be arranged at four or more positions. it can. In actual focus detection, the photographer manually operates the operation unit 28 from among a plurality of focus detection pixel rows 22a to 22c, and selects a desired focus detection pixel row as a focus detection position. You can also.

  FIG. 5A is an enlarged front view showing one of the focus detection pixels 222a, and FIG. 7A is a cross-sectional view of the focus detection pixel 222a. FIG. 5B is an enlarged front view showing one of the focus detection pixels 222b, and FIG. 7B is a cross-sectional view of the focus detection pixel 222b. As shown in FIG. 5A, the focus detection pixel 222a includes a micro lens 2221a and a semicircular photoelectric conversion unit 2222a. As shown in the cross-sectional view of FIG. A photoelectric conversion portion 2222a is formed on the surface of the semiconductor circuit substrate 2213, and a micro lens 2221a is formed on the surface. The focus detection pixel 222b includes a micro lens 2221b and a photoelectric conversion unit 2222b as shown in FIG. 5B, and a semiconductor of the image sensor 22 as shown in a cross-sectional view of FIG. 7B. A photoelectric conversion unit 2222b is formed on the surface of the circuit board 2213, and a microlens 2221b is formed on the surface. Then, as shown in FIG. 3, these focus detection pixels 222a and 222b are alternately arranged adjacent to each other in a horizontal row, thereby forming focus detection pixel rows 22a to 22c shown in FIG.

  The photoelectric conversion units 2222a and 2222b of the focus detection pixels 222a and 222b have such a shape that the microlenses 2221a and 2221b receive a light beam that passes through a predetermined region (eg, F2.8) of the exit pupil of the photographing optical system. Is done. Further, the focus detection pixels 222a and 222b are not provided with color filters, and their spectral characteristics are the total of the spectral characteristics of a photodiode that performs photoelectric conversion and the spectral characteristics of an infrared cut filter (not shown). ing. However, it may be configured to include one of the same color filters as the imaging pixel 221, for example, a green filter.

  In addition, although the photoelectric conversion units 2222a and 2222b of the focus detection pixels 222a and 222b illustrated in FIGS. 5A and 5B have a semicircular shape, the shapes of the photoelectric conversion units 2222a and 2222b are not limited thereto. Other shapes such as an elliptical shape, a rectangular shape, and a polygonal shape can also be used.

  Here, a so-called phase difference detection method for detecting the focus state of the photographing optical system based on the pixel outputs of the focus detection pixels 222a and 222b described above will be described.

  FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG. 3. The focus detection pixels 222 a-1, 222 b-1, 222 a-2, and 222 b-2 that are arranged in the vicinity of the photographing optical axis L 1 and adjacent to each other are It shows that light beams AB1-1, AB2-1, AB1-2, and AB2-2 irradiated from the distance measuring pupils 341 and 342 of the exit pupil 34 are received, respectively. 8 illustrates only the focus detection pixels 222a and 222b that are located in the vicinity of the photographing optical axis L1, but other focus detection pixels other than the focus detection pixels illustrated in FIG. 8 are illustrated. In the same manner, the light beams emitted from the pair of distance measuring pupils 341 and 342 are respectively received.

  Here, the exit pupil 34 is an image set at a distance D in front of the microlenses 2221a and 2221b of the focus detection pixels 222a and 222b arranged on the planned focal plane of the photographing optical system. The distance D is a value uniquely determined according to the curvature and refractive index of the microlens, the distance between the microlens and the photoelectric conversion unit, and the distance D is referred to as a distance measurement pupil distance. The distance measurement pupils 341 and 342 are images of the photoelectric conversion units 2222a and 2222b respectively projected by the micro lenses 2221a and 2221b of the focus detection pixels 222a and 222b.

  In FIG. 8, the arrangement direction of the focus detection pixels 222a-1, 222b-1, 222a-2, 222b-2 coincides with the arrangement direction of the pair of distance measuring pupils 341, 342.

  As shown in FIG. 8, the microlenses 2221a-1, 2221b-1, 2221a-2, and 2221b-2 of the focus detection pixels 222a-1, 222b-1, 222a-2, and 222b-2 are photographic optical systems. Near the planned focal plane. The shapes of the photoelectric conversion units 2222a-1, 2222b-1, 2222a-2, 2222b-2 arranged behind the micro lenses 2221a-1, 2221b-1, 2221a-2, 2221b-2 are the same as the micro lenses 2221a-1, 2221b-1, 2221a-2, 2221b-2. Projected onto the exit pupil 34 separated from the lenses 2221a-1, 2221b-1, 2221a-2, 2221b-2 by the distance measurement distance D, and the projection shape forms the distance measurement pupils 341, 342.

  In other words, on the exit pupil 34 at the distance measurement distance D, the microlens and the photoelectric conversion unit in each focus detection pixel so that the projection shapes (the distance measurement pupils 341 and 342) of the photoelectric conversion unit of each focus detection pixel match. Is determined, and the projection direction of the photoelectric conversion unit in each focus detection pixel is thereby determined.

  As shown in FIG. 8, the photoelectric conversion unit 2222a-1 of the focus detection pixel 222a-1 is formed on the microlens 2221a-1 by the light beam AB1-1 that passes through the distance measuring pupil 341 and goes to the microlens 2221a-1. A signal corresponding to the intensity of the image to be output is output. Similarly, the photoelectric conversion unit 2222a-2 of the focus detection pixel 222a-2 passes through the distance measuring pupil 341, and the intensity of the image formed on the microlens 2221a-2 by the light beam AB1-2 toward the microlens 2221a-2. The signal corresponding to is output.

  Further, the photoelectric conversion unit 2222b-1 of the focus detection pixel 222b-1 passes through the distance measuring pupil 342, and the intensity of the image formed on the microlens 2221b-1 by the light beam AB2-1 directed to the microlens 2221b-1. Output the corresponding signal. Similarly, the photoelectric conversion unit 2222b-2 of the focus detection pixel 222b-2 passes through the distance measuring pupil 342, and the intensity of the image formed on the microlens 2221b-2 by the light beam AB2-2 toward the microlens 2221b-2. The signal corresponding to is output.

  Then, a plurality of the above-described two types of focus detection pixels 222a and 222b are arranged in a straight line as shown in FIG. 3, and the outputs of the photoelectric conversion units 2222a and 2222b of the focus detection pixels 222a and 222b are converted into the distance measurement pupil 341, respectively. Of the pair of images formed on the focus detection pixel row by the focus detection light fluxes that pass through each of the distance measurement pupil 341 and the distance measurement pupil 342. Data relating to the distribution (hereinafter also referred to as a first data string and a second data string) is obtained. Then, by applying an image shift detection calculation process such as a correlation calculation process or a phase difference detection process to the first data string and the second data string, an image shift amount by a so-called phase difference detection method can be detected.

  Then, a conversion calculation is performed on the obtained image shift amount according to the center-of-gravity interval of the pair of distance measuring pupils, thereby obtaining a current focal plane with respect to the planned focal plane (the focal point corresponding to the position of the microlens array on the planned focal plane). The deviation of the focal plane at the detection position, that is, the defocus amount can be obtained. The details of the detection method of the image shift amount by the phase difference detection method and the calculation method of the defocus amount will be described later.

  The calculation of the image shift amount by the phase difference detection method and the calculation of the defocus amount based thereon are executed by the camera control unit 21.

  Further, the camera control unit 21 reads the output of the imaging pixel 221 of the imaging element 22 and calculates a focus evaluation value based on the read pixel output. This focus evaluation value can be obtained by, for example, extracting a high frequency component of an image output from the imaging pixel 221 of the imaging element 22 using a high frequency transmission filter and integrating the extracted high frequency component. It can also be obtained by extracting high-frequency components using two high-frequency transmission filters having different cutoff frequencies and integrating them.

  Then, the camera control unit 21 sends a control signal to the lens control unit 37 to drive the focus lens 32 at a predetermined sampling interval (distance) to obtain a focus evaluation value at each position, and the focus evaluation value is maximum. The focus detection by the contrast detection method is performed in which the position of the focus lens 32 is determined as the in-focus position. Note that this in-focus position is obtained when, for example, when the focus evaluation value is calculated while driving the focus lens 32, the focus evaluation value rises twice and then moves down twice. It can be obtained by performing calculations such as interpolation using five focus evaluation values. Note that the number of focus evaluation values used for detecting the peak of the focus evaluation value is preferably five as described above, but is not limited to five and may be three or more. Good. For example, when three focus evaluation values are acquired, and these focus evaluation values rise once and then move down once, using these three focus evaluation values, the focus evaluation value peaks. It is good also as a structure which detects.

  Next, an operation example of the camera 1 according to the present embodiment will be described. FIG. 9 is a flowchart showing an operation example of the camera 1 according to the present embodiment. The following operation is started, for example, when the photographer presses the shutter release button provided in the operation unit 28 halfway. In the following, a description will be given by taking as an example a case where the one-shot mode, that is, the mode in which the focus lens 32 that has been adjusted once is fixed and the mode for photographing at the focus lens position is selected.

  First, in step S101, the aperture value is acquired by the camera control unit 21, and in the subsequent step S102, the first shift calculation range is determined based on the aperture value acquired in step S101 by the camera control unit 21. The process for doing is performed.

  Here, with reference to FIG. 10 and FIG. 11, the relationship between the aperture value and the shift amount of the pair of data strings will be described. FIG. 10A is a diagram illustrating an example of the relationship between the exit pupil 34 and the distance measurement pupils 341 and 342 of the focus detection pixels when the aperture value is F2.8. FIG. It is a figure which shows an example of the relationship between the exit pupil 34 in case a value is F5.6, and the ranging pupils 341 and 342 of a focus detection pixel. 10A and 11A both show a scene in which the defocus amount is also 1 mm, for example (the lens position of the focus lens 32 is at a distance of, for example, 1 mm in terms of the image plane movement amount to the in-focus position). Example).

Compared to the example shown in FIG. 11A, in the example shown in FIG. 10A, the aperture value is F2.8 and the exit pupil 34 is large, so that most of the distance measurement pupils 341 and 342 are exit pupils. 34. Therefore, in the example shown in FIG. 10A, the light receiving areas of the distance measuring pupils 341 and 342 included in the exit pupil 34 are also large, and the barycentric position 351 of the light receiving area of the distance measuring pupil 341 (light reception of the distance measuring pupils 341 and 342). and position) of the center of gravity of the region, also increases the distance between the centers of gravity L ₁ between the center-of-gravity position 352 of the light receiving area of the range-finding pupils 341. On the other hand, compared with the example shown in FIG. 10A, in the example shown in FIG. 11A, the aperture value is F5.6, and the exit pupil 34 is small. Therefore, the distance measuring pupil 341 included in the exit pupil 34 , 342 also has a small light receiving area. Therefore, in the example shown in FIG. 11 (A), also shortens the distance between the centers of gravity L ₂ between the center-of-gravity position 352 of the light receiving area of the center-of-gravity position 351 with range-finding pupils 342 of the light-receiving region of the range-finding pupils 341.

  FIG. 10B shows an example of signal intensities of the first data row and the second data row output from the pair of focus detection pixel rows 22a, 22b, and 22c when the aperture value is F2.8. 11B is a graph showing the first and second data strings output from the pair of focus detection pixel strings 22a, 22b, and 22c when the aperture value is F5.6. It is a graph which shows an example of signal strength. 10 (A) and 11 (A), both FIG. 10 (B) and FIG. 11 (B) exemplify a scene where the defocus amount is 1 mm, for example. 10B and 11B, the horizontal axis indicates the pixel position of each pixel in the focus detection pixel rows 22a, 22b, and 22c.

As shown in FIG. 10B, in the case where the aperture value is F2.8, compared to the case where the aperture value shown in FIG. 11B is F5.6, the light-receiving areas of the distance measurement pupils 341 and 342 are reduced. since the distance between the centers of gravity _{L 1} between the gravity center position 351 and 352 is long, the deviation amount _{W 1} between the first and second data streams increases. On the other hand, as shown in FIG. 11B, in the case where the aperture value is F5.6, compared to the case where the aperture value shown in FIG. is short distance between the centroids L ₂ between the center of gravity position 351 and 352 of the light receiving area, the deviation amount W ₂ between the first and second data streams is reduced. As described above, even when the defocus amount is the same, the shift amount between the first data row and the second data row may differ depending on the aperture value.

  In the present embodiment, as described later, the correlation amount between the first data string and the second data string is calculated while shifting the first data string and the second data string within a predetermined shift range, and the correlation is calculated. The shift amount that provides the extreme value of the amount is detected as the shift amount between the first data string and the second data string. Therefore, as described above, if the shift amount between the first data string and the second data string changes according to the aperture value, a shift range for shifting the first data string and the second data string is set. When the amount of deviation between the first data row and the second data row becomes too small and the defocus amount cannot be calculated, or the shift range becomes too large, the defocus amount It may take a long time to calculate.

Therefore, in step S102, the camera control unit 21 performs the first operation as shown in the following equation (1) so that the amount of deviation between the first data sequence and the second data sequence can be detected appropriately. A shift range for shifting the data string and the second data string is determined as the first shift calculation range Sna based on the aperture value.
Sna = So × (k1 / k2) (1)
In the above equation (1), So is a shift range that is a reference for determining the first shift calculation range. For example, when the aperture value is F5.6 and the defocus amount is 1 mm, A shift range in which the extreme value of the correlation amount between the first data string and the second data string can be obtained by relatively shifting the one data string and the second data string (the aperture value is F5.6). The shift range in which the extreme value of the correlation amount can be obtained when the lens position of the focus lens 32 is at a distance of 1 mm in terms of image plane movement to the in-focus position. In addition, So is not limited to the above-described range. For example, when the defocus amount is 5 mm at a predetermined aperture value, the extreme value of the correlation amount between the first data string and the second data string is obtained. It is also possible to set a shift range in which In the above equation (1), k1 is a reference shift range among conversion coefficients (conversion coefficients will be described later) for converting a shift amount for obtaining an extreme value of the correlation amount into a defocus amount. A conversion coefficient corresponding to the aperture value of So, for example, a shift that can obtain an extreme value of the correlation amount when the standard shift range So is an aperture value of F2.8 and a defocus amount of 1 mm. When set as a range, k1 is a conversion coefficient corresponding to the aperture value F2.8. Further, in the above equation (1), k2 is a conversion coefficient corresponding to the aperture value acquired in step S101, among the conversion coefficients for converting the shift amount from which the extreme value of the correlation amount is obtained into the defocus amount. is there.

  For example, the reference shift range So is a shift range in which the extreme value of the correlation amount can be obtained when the aperture value is F5.6 and the defocus amount is 1 mm, and the aperture value acquired in step S101 is In the case of F2.8, when the conversion coefficient k1 at the aperture value F5.6 is, for example, twice the conversion coefficient k2 at the aperture value F2.8, based on the above equation (1), The 1-shift calculation range Sna can be determined as a range twice as large as the shift range So at the aperture value F5.6. Note that Sna and So are both integers. In this embodiment, when the first shift calculation range Sna is obtained, the decimal part of So × (k1 / k2) is rounded and Sna is calculated as an integer.

Note that the method for determining the first shift calculation range is not particularly limited to the above-described method. For example, since the conversion coefficient corresponding to the aperture value and the aperture value have a substantially linear relationship, the shift amount is determined as the defocus amount. The first shift calculation range may be determined using the aperture value as it is, instead of the conversion coefficient for converting to. Specifically, the first shift calculation range Sna may be determined based on the following formula (2).
Sna = So × (f1 / f2) (2)
In the above formula (2), f1 is the aperture value in the reference shift range So, and f2 is the aperture value acquired in step S101.

  In step S103, the camera control unit 21 performs the defocus amount calculation in the first shift calculation range determined in step S102. Specifically, the camera control unit 21 performs an image shift detection calculation process (correlation calculation process) based on the first data string and the second data string read from the focus detection pixels 222a and 222b, and the first data string. And the second data string are calculated, and the defocus amount is calculated based on the calculated shift amount.

Specifically, first, the camera control unit 21 first data columns a ₁ , a ₂ ,... Read from the focus detection pixel columns 22a, 22b, and 22c. . . , _An and the second data string b ₁ , b ₂ ,. . . While _n is relatively shifted in a one-dimensional manner within the first shift calculation range determined in step S102, the correlation calculation shown in the following equation (3) is performed.
C (k) = Σ | a (n + k) −b (n) | (3)
In the above equation (3), the Σ operation indicates a cumulative operation (phase sum operation) for n. The image shift amount k is an integer, and is a shift amount in units of pixel intervals of the focus detection pixel rows 22a to 22c. In this embodiment, since the correlation calculation is performed by shifting the first data string and the second data string in the first shift calculation range, the image shift amount k is the first shift calculation range within the first shift calculation range. The shift amount is limited to a shift amount that can shift the one data string and the second data string. In the calculation result of the above formula (3), the correlation amount C (k) is minimal (the correlation degree is higher as the correlation is smaller) in the shift amount where the correlation between the first data sequence and the second data sequence is high. Become.

Next, the camera control unit 21 uses the three-point interpolation method shown in the following formulas (4) to (7) below to determine the shift amount x that provides the minimum value C (x) for the continuous correlation amount. Ask. Note that C (kj) shown in the following equation is the smallest value among the correlation amounts C (k) obtained by the above equation (3).
D = {C (kj−1) −C (kj + 1)} / 2 (4)
C (x) = C (kj) − | D | (5)
x = kj + D / SLOP (6)
SLOP = MAX {C (kj + 1) -C (kj), C (kj-1) -C (kj)} (7)

  Furthermore, the camera control unit 21 determines the reliability of the shift amount x that provides the minimum value C (x) of the correlation amount. For example, when the correlation between the pair of data strings is low, the camera control unit 21 increases the value of the interpolated correlation minimum value C (x), so that C (x) is equal to or greater than a predetermined threshold value. In addition, it can be determined that the reliability of the calculated shift amount is low. Further, the camera control unit 21 calculates C (x) when the value obtained by dividing C (x) by SLOP that is proportional to the contrast is equal to or greater than a predetermined value in order to normalize C (x) with the data contrast. It can be determined that the reliability of the shift amount is low. Further, the camera control unit 21 can determine that the subject has low contrast and the reliability of the calculated shift amount is low when SLOP, which is a value proportional to the contrast, is equal to or less than a predetermined value.

Then, the camera control unit 21 calculates the defocus amount df according to the following equation (8) based on the shift amount x from which the minimum value C (x) of the correlation amount is obtained.
df = x · k · p (8)
In the above equation (8), k is a conversion coefficient for converting the shift amount x from which the minimum value C (x) of the correlation amount is obtained into the defocus amount. As described above, since the shift amount for obtaining the extreme value of the correlation amount differs depending on the aperture value, the conversion coefficient is preset according to the aperture value. Further, p is a constant determined by the pitch width of the focus detection pixels 222a and 222b constituting the focus detection pixel rows 22a to 22c.

  Next, in step S104, the camera control unit 21 calculates the lens driving amount necessary to drive the focus lens 32 to the in-focus position based on the defocus amount calculated in step S103. The obtained lens driving amount is sent to the focus lens driving motor 36 via the lens control unit 37. Thereby, the lens driving amount is acquired by the focus lens driving motor 36, and the driving of the focus lens 32 is started based on the acquired lens driving amount.

  In step S105, the camera control unit 21 performs a process for determining a second shift calculation range narrower than the first shift calculation range based on the calculation result of the defocus amount calculation in step S103 or step S106. The In the subsequent step S106, the camera control unit 21 performs the defocus amount calculation in the second shift calculation range determined in step S105. Thus, in this embodiment, even when driving of the focus lens 32 to the in-focus position is started in step S104, the defocus amount is calculated while driving the focus lens 32 in steps S105 and S106. The process is executed.

Here, the shift amount between the first data string and the second data string becomes smaller as the focus lens 32 approaches the in-focus position. Therefore, the shift range for calculating the correlation amount between the first data string and the second data string can also be reduced as the focus lens 32 approaches the in-focus position. Therefore, in step S105, in order to set the shift range for calculating the correlation amount to an appropriate size range in accordance with the driving of the focus lens 32 to the in-focus position, it is obtained in step S103 or step S106. Based on the calculation result of the defocus amount calculation, a second shift calculation range Snp that satisfies the relationship of the following equation (9) is determined.
Snp ≦ | Sf | + Sp (where Snp <Sna) (9)
In the above equation (9), Sf is the shift amount x that gives the minimum value C (x) of the correlation amount obtained by the defocus amount calculation in step S103 or step S106. Sp is a shift range necessary at least for detecting the minimum value C (x) of the correlation amount. For example, when obtaining the minimum value C (x) of the correlation amount by the three-point interpolation method, A shift range in which three correlation amounts between the first data string and the second data string can be obtained while relatively shifting the first data string and the second data string can be obtained.

  In addition, since the shift range can be reduced as the focus lens 32 approaches the in-focus position, in the present embodiment, the second shift calculation range Snp is determined before driving the focus lens 32 to the in-focus position. The range is determined to be smaller than the first shift calculation range Sna. The second shift calculation range Snp is an integer, and when the second shift calculation range Snp is obtained in the present embodiment, the second shift calculation range Snp is calculated as an integer by rounding off the decimal part of Sf.

  In step S106, the camera control unit 21 performs a defocus amount calculation in the second shift calculation range determined in step S105. Note that the defocus amount calculation in step S106 performs a correlation calculation between the first data string and the second data string while shifting the first data string and the second data string in the second shift calculation range. Except for this, it can be performed by the same method as the defocus amount calculation in step S104.

  In step S107, the camera control unit 21 performs in-focus determination. In the present embodiment, for example, when the defocus amount calculated in step S106 is equal to or less than a predetermined value, it is determined to be in focus, and the process proceeds to step S108. On the other hand, if the defocus amount exceeds the predetermined value and is not determined to be in focus, the process returns to step S105, and the determination of the second shift calculation range and the determination in the second shift calculation range are performed until the defocus amount is equal to or less than the predetermined value. The defocus amount calculation is repeatedly executed.

  If the process returns to step S105 without being determined to be in focus, the lens position of the focus lens 32 is closer to the focus position than when the second shift calculation range was previously determined. Therefore, when the camera control unit 21 newly determines the second shift calculation range in step S105, the camera control unit 21 sets the second shift calculation range to the previously determined second shift calculation range based on the above equation (9). Decide on a smaller range. As described above, in this embodiment, the shift range in which the first data string and the second data string are shifted can be reduced as the focus lens 32 approaches the in-focus position.

  If it is determined in step S107 that the in-focus state is obtained, the process proceeds to step S108, where focus lock (processing for prohibiting driving of the focus lens 32) is performed. Thereby, the operation of the camera 1 ends.

  As described above, in the present embodiment, the first shift calculation range is determined based on the aperture value, and the first shift calculation range output from the pair of focus detection pixel rows 22a, 22b, and 22c in the determined first shift calculation range. While shifting the first data string and the second data string, the amount of correlation between the first data string and the second data string is detected, and the shift amount that provides the extreme value of the correlation amount is detected. As described above, in this embodiment, the shift range in which the first data string and the second data string are shifted is determined according to the aperture value, and depending on the aperture value, the first data sequence and the second data sequence are determined. It is possible to effectively prevent the shift range from becoming too small and the defocus amount from being unable to be calculated with respect to the deviation amount, and thus focus detection accuracy can be improved. Further, by determining the shift range for shifting the first data string and the second data string according to the aperture value, depending on the aperture value, the shift amount between the first data sequence and the second data sequence is Since it can be effectively prevented that the shift range becomes too large and the time for calculating the defocus amount becomes long, it is possible to improve the response in focus detection.

  In the present embodiment, a second shift calculation range smaller than the first shift calculation range is determined based on the calculation result of the defocus amount calculation while driving the focus lens 32 to the in-focus position. Then, the defocus amount calculation is executed in the determined second shift calculation range. In particular, in this embodiment, the closer the focus lens 32 is to the in-focus position, the smaller the amount of deviation between the first data row and the second data row is. Therefore, as the focus lens 32 approaches the in-focus position, The 2-shift calculation range is determined to be a small range. Thereby, in this embodiment, the time for calculating the defocus amount can be further shortened. Therefore, for example, the number of times of defocus amount calculation can be increased until the focus lens 32 is driven to the in-focus position, and the focus detection accuracy can be further increased.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  For example, in the above-described embodiment, when the first shift calculation range is determined according to the aperture value, as shown in the equation (1), the predetermined shift range So corresponding to the predetermined aperture value is used as a reference. The first shift calculation range is calculated. For example, when continuous shooting is performed in the continuous mode, the reference shift range So is set to be higher than usual in consideration of the shooting speed of continuous shooting. It is good also as a structure which makes a 1st shift calculation range a range smaller than usual by setting to a small range. Further, when the defocus amount cannot be calculated at the current lens position of the focus lens 32, in a scanning operation in which the defocus amount is calculated at a different lens position while driving the focus lens 32, the focus detection accuracy is increased. The reference shift range So may be set to a range larger than normal so that the first shift calculation range is larger than normal. In this case, if the time for calculating the defocus amount becomes longer by setting the first shift calculation range to a range larger than usual, the balance between the focus detection accuracy and the defocus amount calculation time is taken into consideration. In addition, for example, instead of performing the correlation operation between the first data string and the second data string while shifting the first data string and the second data string at an interval of one pixel, the first data string The second data string and the second data string may be shifted at intervals of two pixels, and the correlation calculation between the first data string and the second data string may be performed.

  In the above-described embodiment, the second shift calculation range is determined based on the calculation result of the defocus amount calculation while the focus lens 32 is being driven to the in-focus position, and the determined second shift is determined. In the calculation range, the configuration for performing the defocus amount calculation is exemplified, but in this case, the reliability of the calculation result of the defocus amount calculation is further determined, and only when the reliability is determined to be greater than or equal to the predetermined value, The second shift calculation range may be determined based on the calculation result of the defocus amount calculation, and the defocus amount calculation may be performed in the determined second shift calculation range. Further, in this case, when it is determined that the reliability of the calculation result of the defocus amount calculation is less than the predetermined value, the first shift calculation determined based on the aperture value in order to effectively prevent false focusing. The defocus amount calculation may be performed in the range. In addition, when the first shift calculation range is determined by the operation of the camera 1, such as when continuous shooting is performed in the continuous mode or when a scan operation is performed, the size of the shift range So serving as a reference changes. May be configured to perform the defocus amount calculation in a smaller range of the first shift calculation range Sna and the second shift calculation range Spn.

  Furthermore, in the above-described embodiment, the configuration in which focus detection is performed by the phase difference detection method has been illustrated. However, in addition to this configuration, for example, focus detection is performed by the phase difference detection method, and the focus state is detected by the phase difference detection method. If this is not possible, focus detection may be performed using a contrast detection method. Alternatively, a configuration may be adopted in which focus detection is performed by the phase difference detection method, and focus detection by the phase difference detection method and focus detection by the contrast detection method are performed simultaneously when the focus state cannot be detected by the phase difference detection method.

  The camera 1 of the above-described embodiment is not particularly limited. For example, the present invention is applied to other optical devices such as a digital video camera, a single-lens reflex digital camera, a lens-integrated digital camera, and a camera for a mobile phone. May be.

DESCRIPTION OF SYMBOLS 1 ... Digital camera 2 ... Camera body 21 ... Camera control part 22 ... Imaging device 221 ... Imaging pixel 222a, 222b ... Focus detection pixel 24 ... Memory 28 ... Operation part 3 ... Lens barrel 32 ... Focus lens 36 ... Focus lens drive motor 37 ... Lens control unit

Claims (6)

An imaging unit including an imaging pixel that captures an image by an optical system and outputs an image signal corresponding to the captured image; and a pair of focus detection pixel rows that receive a pair of pupil-divided light beams;
While the first data row and the second data row respectively output from the pair of focus detection pixel rows are relatively shifted in a one-dimensional manner, between the first data row and the second data row. A phase difference detection unit that detects a focus state of the optical system by calculating a correlation amount and detecting a shift amount at which an extreme value of the correlation amount is obtained;
A diaphragm that passes through the optical system and restricts a light beam incident on the imaging unit;
A shift calculation range in which the first data sequence and the second data sequence are relatively shifted when detecting the shift amount at which the extreme value of the correlation amount is obtained based on the aperture value by the aperture is defined as a first range. And a control unit that determines the shift calculation range and causes the phase difference detection unit to calculate the correlation amount in the first shift calculation range. The focus detection apparatus according to claim 1,
The focus detection device, wherein the control unit sets the first shift calculation range to a smaller range as the aperture value by the aperture is larger. The focus detection apparatus according to claim 1 or 2,
A contrast detection unit that detects a focus state of the optical system by calculating an evaluation value related to a contrast of the image by the optical system based on the image signal output by the imaging pixel, Focus detection device. The focus detection apparatus according to claim 1,
The control unit detects the extreme value of the detected correlation amount when a shift amount at which the extreme value of the correlation amount is obtained is detected and the reliability of the calculation result of the correlation amount is equal to or greater than a predetermined value. A second shift calculation range that is narrower than the first shift calculation range is determined based on a shift amount from which a value is obtained, and the phase difference detection unit calculates the correlation amount in the second shift calculation range. A focus detection apparatus. The focus detection apparatus according to claim 4,
The control unit determines a shift amount at which the extreme value of the correlation amount is obtained when the focus adjustment lens is driven to the in-focus position based on the shift amount at which the extreme value of the correlation amount is obtained. It is detected and the reliability of the calculation result of the correlation amount is determined to be equal to or greater than a predetermined value, and based on the determination result, the correlation is sent to the phase difference detection unit in the second shift calculation range. A focus detection apparatus that determines whether or not to perform an amount calculation.   An imaging device provided with the focus detection apparatus in any one of Claims 1-5.

Images