JP2014211589A - Focus adjustment device and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus adjustment device capable of performing focus adjustment excellently.SOLUTION: The focus adjustment device includes an imaging element for capturing an image formed by an optical system having a focus lens, and outputs an image signal. For a focus detection area A1 in an imaging screen, the focus adjustment device calculates a focus lens position, as a first lens position, at which an evaluation value of image contrast becomes maximum. In addition, for an extension area A2 including the focus detection area A1 and being wider than the focus detection area A1, the focus adjustment device calculates a focus lens position, as a second lens position, at which the evaluation value of image contrast becomes maximum. When the maximum value of the evaluation value calculated for the focus detection area A1 is equal to or larger than a determination threshold, the focus adjustment device determines the first lens position or the second lens position as an in-focus lens position, by using the difference between the first lens position and the second lens position.

Description

  The present invention relates to a focus adjustment device and an imaging apparatus including the focus adjustment device.

2. Description of the Related Art Conventionally, a technique for detecting a focus state of an optical system by calculating a focus evaluation value associated with driving of a focus lens for a focus detection area set in a shooting screen is known. In such a technique, for example, a true / false determination area including a focus detection area set in the shooting screen and wider than the focus detection area is set, and the peak position of the focus evaluation value in the focus detection area and the true / false are set. A technique for defocusing is known in order to avoid false focusing when the focus evaluation value peak position in the determination area is more than a predetermined distance (see, for example, Patent Document 1). ).
However, in the prior art, when the peak position of the focus evaluation value in the focus detection area and the peak position of the focus evaluation value in the authenticity determination area are more than a predetermined distance, the focus is uniformly out of focus. Actually, there is a problem that even when false focus is not achieved, it is determined that the image is out of focus.

Japanese Patent No. 4902946

  The problem to be solved by the present invention is to provide a focus adjustment device that can perform focus adjustment satisfactorily.

  The present invention solves the above problems by the following means.

  [1] A focus adjustment apparatus according to the present invention captures an image by an optical system having a focus lens, outputs an image signal corresponding to the captured image, and drives and controls the focus lens in the optical axis direction. Thus, the drive control unit that changes the focus state of the optical system, and the evaluation value related to the contrast of the image by the optical system based on the image signal output from the image sensor for the first region in the shooting screen And a first lens position calculation that calculates a position in the optical axis direction of the focus lens corresponding to the maximum evaluation value calculated for the first region as a first lens position. And the second region in the photographing screen that includes the first region and is wider than the first region, based on the image signal output from the image sensor, the optical A second evaluation value calculation unit for calculating an evaluation value related to the contrast of the image by the image sensor, and a position in the optical axis direction of the focus lens corresponding to the maximum value of the evaluation value calculated for the second region as a second lens position A second lens position calculation unit to be calculated; a first determination unit that determines whether or not a maximum evaluation value calculated for the first region is equal to or greater than a predetermined determination threshold; and a calculation for the first region When the maximum evaluated value is equal to or greater than the determination threshold, the difference between the first lens position and the second lens position is used to focus the first lens position or the second lens position. And a focusing lens position determination unit that determines the lens position.

  [2] In the focus adjustment apparatus of the present invention, when the difference between the first lens position and the second lens position is equal to or less than a predetermined first difference value, the focusing lens position determination unit A first lens position is selected as a focus lens position, and a difference between the first lens position and the second lens position is greater than the first difference and a predetermined second difference greater than the first difference value. If the second lens position is selected as the in-focus lens position and the difference between the first lens position and the second lens position is greater than the second difference value. It can be configured to determine that it is out of focus.

  [3] The focus adjustment apparatus of the present invention further includes an acquisition unit that acquires information on an effective focal length of the optical system set for each position of the focus lens in the optical axis direction, and the focus lens position determination unit The first lens position is only when the change amount of the effective focal length with respect to the change amount of the position of the focus lens in the optical axis direction in the vicinity of the first lens position is equal to or greater than a predetermined change amount threshold value. And a process of determining the first lens position or the second lens position as a focusing lens position based on a difference between the first lens position and the second lens position.

  [4] The focus adjustment apparatus of the present invention further includes an acquisition unit that acquires information on an effective focal length of the optical system set for each position of the focus lens in the optical axis direction, and the second evaluation value calculation unit However, the size of the second region can be set according to the change amount of the effective focal length with respect to the change amount of the position of the focus lens in the optical axis direction.

  [5] The focus adjustment apparatus of the present invention further includes an acquisition unit that acquires information on an effective focal length of the optical system set for each position of the focus lens in the optical axis direction, and the focusing lens position determination unit However, the first difference value and the second difference value can be set according to the change amount of the effective focal length with respect to the change amount of the position of the focus lens in the optical axis direction.

  [6] The focus adjustment apparatus of the present invention further includes a mode setting unit capable of setting a plurality of the first regions in the shooting screen, and the focusing lens position determination unit is Only when the number of the first regions in the shooting screen is set to one, the first lens position or the second lens position is based on the difference between the first lens position and the second lens position. A process for determining the lens position as the in-focus lens position may be executed.

  [7] An imaging apparatus according to the present invention includes any one of the focus adjustment apparatuses described above.

  ADVANTAGE OF THE INVENTION According to this invention, the focus adjustment apparatus which can perform a focus adjustment favorably can be provided.

FIG. 1 is a block diagram showing a camera according to the present embodiment. FIG. 2 is a front view showing an 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. 4A is an enlarged front view showing one of the imaging pixels 221, FIG. 4B is an enlarged front view showing one of the focus detection pixels 222a, and FIG. FIG. 4D is an enlarged front view showing one of the focus detection pixels 222b, FIG. 4D is a cross-sectional view showing one of the imaging pixels 221 in an enlarged manner, and FIG. 4E is one of the focus detection pixels 222a. FIG. 4F is an enlarged sectional view showing one of the focus detection pixels 222b. FIG. 5 is a sectional view taken along line VIII-VIII in FIG. FIGS. 6A and 6B are diagrams illustrating an example of a change in the angle of view caused by driving the focus lens 33. FIG. FIG. 7 is a diagram showing the relationship between the lens position of the focus lens 33 and the focus evaluation value in the scene shown in FIG. FIG. 8A and FIG. 8B are diagrams for explaining the operation of this embodiment in one scene example. FIG. 9 is a diagram showing the relationship between the lens position of the focus lens 33 and the focus evaluation value in the scene shown in FIG. FIG. 10 is a flowchart showing an operation example of this embodiment. FIG. 11A and FIG. 11B are diagrams for explaining the operation of the present embodiment in another scene example. FIG. 12 is a diagram illustrating the relationship between the lens position of the focus lens 33, the focus evaluation value, and the effective focal length.

  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 photographing optical system including lenses 31, 32, 33, 34 and a diaphragm 35.

  The lens 33 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 33 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 331 while its position is detected by the encoder 332. The current position information of the focus lens 33 detected by the encoder 332 is sent to the camera control unit 21 to be described later via the lens control unit 36, and the focus lens driving motor 331 calculates the focus lens calculated based on this information. The drive position 33 is driven by being sent from the camera control unit 21 via the lens control unit 36.

  The lens 32 is a zoom lens, and can move in the optical axis L1 direction to adjust the shooting magnification of the shooting optical system. Similarly to the focus lens 33 described above, the position of the zoom lens 32 is adjusted by the zoom lens driving motor 321 while the position thereof is detected by the zoom lens encoder 322. The position of the zoom lens 32 is adjusted by operating a zoom button provided on the operation unit 28 or operating a zoom ring (not shown) provided on the camera barrel 3.

  The diaphragm 35 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 adjust the amount of blur. The adjustment of the aperture diameter by the diaphragm 35 is performed, for example, by sending an appropriate aperture diameter calculated in the automatic exposure mode from the camera control unit 21 via the lens control unit 36. Further, the set aperture diameter is input from the camera control unit 21 to the lens control unit 36 by a manual operation by the operation unit 28 provided in the camera body 2. The aperture diameter of the aperture 35 is detected by an aperture sensor (not shown), and the lens controller 36 recognizes the current aperture diameter.

  The lens memory 37 is a memory that stores various lens information such as information on the shooting distance of the lens barrel 3 and the driving speed of the focus lens 33. In addition, the lens memory 37 includes a lens position-effective focal length table indicating the relationship between the lens position of the focus lens 33 in the optical axis L1 direction and the effective focal length at the lens position. Even when the lens position of the focus lens 33 is the same, if the lens position of the zoom lens 32 is different, the effective focal length is also different. A lens position-effective focal length table is provided.

  The lens control unit 36 is electrically connected to the camera control unit 21 by an electrical signal contact unit 41 provided on the mount unit 4, and drives the zoom lens 32 and the focus lens 33 based on a command from the camera control unit 21. And the lens diameter, such as the position of the zoom lens 32, the position of the focus lens 33, and the aperture diameter of the diaphragm 35, are transmitted to the camera control unit 21. The lens control unit 36 refers to the lens position-effective focal length table stored in the lens memory 37 and transmits the effective focal length at the current lens position of the focus lens 33 to the camera control unit 21.

  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 camera memory 24 which is a recording medium. The camera memory 24 can be either a removable card type memory or a built-in memory. 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.

  The camera body 2 is provided with a camera control unit 21. The camera control unit 21 is electrically connected to the lens control unit 36 through an electrical signal contact unit 41 provided on the mount unit 4, receives lens information from the lens control unit 36, and defocuses to the lens control unit 36. 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. Are output to the liquid crystal drive circuit 25 and the camera 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 an input switch for a photographer to set various operation modes of the camera 1 such as a shutter release button and a moving image shooting start switch. The operation unit 28 switches between an auto focus mode / manual focus mode and an auto focus mode. In particular, the one-shot mode / continuous mode can be switched. 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.

  4A is an enlarged front view showing one of the imaging pixels 221 and FIG. 4D is a cross-sectional view. One imaging pixel 221 includes a microlens 2211, a photoelectric conversion unit 2212, and a color filter (not shown), and on the surface of the semiconductor circuit substrate 2213 of the imaging element 22 as shown in the cross-sectional view of FIG. A photoelectric conversion portion 2212 is built, and a microlens 2211 is formed on the surface thereof. 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 imaging surface of the imaging 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 positions shown in the figure, and may be any one, two, or the like, and are arranged at four or more positions. You can also. In actual focus detection, the user manually operates the operation unit 28 from among the 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.

  4B is an enlarged front view of one of the focus detection pixels 222a, and FIG. 4E is a cross-sectional view of the focus detection pixel 222a. 4C is an enlarged front view showing one of the focus detection pixels 222b, and FIG. 4F is a cross-sectional view of the focus detection pixel 222b. As shown in FIG. 4B, 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. 4C, and a semiconductor of the image sensor 22 as shown in the cross-sectional view of FIG. 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. 4B and 4C have a semicircular shape, the shape of the photoelectric conversion units 2222a and 2222b is 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. 5 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 351 and 352 of the exit pupil 350 are received. In FIG. 5, only the focus detection pixels 222 a and 222 b that are located in the vicinity of the photographing optical axis L <b> 1 are illustrated, but other focus detection pixels other than the focus detection pixels illustrated in FIG. 5 are illustrated. In the same manner, the light beams emitted from the pair of distance measuring pupils 351 and 352 are respectively received.

  Here, the exit pupil 350 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 351 and 352 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. 5, the arrangement direction of the focus detection pixels 222 a-1, 222 b-1, 222 a-2, and 222 b-2 coincides with the arrangement direction of the pair of distance measuring pupils 351 and 352.

  As shown in FIG. 5, 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 Projected onto the exit pupil 350 that is separated from the lenses 2221 a-1, 2221 b-1, 2221 a-2, and 2221 b-2 by a distance measurement distance D, and the projection shape forms distance measurement pupils 351 and 352.

  That is, the microlens and the photoelectric conversion unit in each focus detection pixel so that the projection shapes (distance measurement pupils 351 and 352) of the focus detection pixels coincide on the exit pupil 350 at the distance D. Is determined, and the projection direction of the photoelectric conversion unit in each focus detection pixel is thereby determined.

  As shown in FIG. 5, the photoelectric conversion unit 2222a-1 of the focus detection pixel 222a-1 is formed on the microlens 2221a-1 by a light beam AB1-1 that passes through the distance measuring pupil 351 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 351, 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 352, 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 352, 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 used as the distance measurement pupil 351. Of the pair of images formed on the focus detection pixel array by the focus detection light fluxes passing through each of the distance measurement pupil 351 and the distance measurement pupil 352. Data on the distribution 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 intensity distribution data, 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 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 33 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 33 is determined as the in-focus position. Note that the calculation of the focus evaluation value and the focus detection based on the contrast detection method based on the calculation are performed corresponding to a predetermined focus detection area A1 provided in the shooting screen.

  Hereinafter, focus detection by the contrast detection method in the present embodiment will be described in detail. Hereinafter, as shown in FIG. 6A, a case where the focus detection area A1 is set in a predetermined area including the center of the shooting screen will be described as an example. Here, in FIG. 6A, “mountains” and “trees” exist in the shooting screen, and “mountains” are captured in the focus detection area A1, and “trees” are in the focus detection area A1. It is a scene that is out of the range. In such a case, when the focus lens 33 is search-driven from the infinity side to the close side in order to perform focus detection by the contrast detection method, as shown in FIG. When the lens position 33 is on the infinity side, the focus lens 33 is driven to the closest side even when there is no “tree” in the focus detection area A 1. As the distance changes and the angle of view changes, as shown in FIG. 6B, when the lens position of the focus lens 33 moves to the close side, “tree” enters the focus detection area A1. It will end up.

  In such a case, the focus evaluation value calculated from the luminance information in the focus detection area A1 is as shown in FIG. That is, as shown in FIG. 7, at the beginning of driving the focus lens 33 from the infinity side to the close side, “trees” do not enter the focus detection area A1, and “mountains” exist. Therefore, first, a peak (maximum value) is detected at the lens position L1 corresponding to the image plane position of “mountain”. However, on the other hand, when the focus lens 33 is further driven closer, as shown in FIG. 6B, the effective focal length changes and the angle of view changes as the focus lens 33 is driven. Consequently, “tree” enters the focus detection area A1, and as a result, as shown in FIG. 7, a peak due to “tree” is detected at the lens position L3.

  Here, the lens position corresponding to the image plane position of “tree” is the position of L2 as shown in FIG. 7, whereas in the example shown in FIGS. 6A and 6B. The peak due to the “tree” is detected as a false peak at the position of L3. In particular, the false peak detected at the position of L3 is not the actual image plane position of “tree”, but when “tree” enters the focus detection area A1 due to the change in the angle of view accompanying the drive of the focus lens 33. In general, it does not coincide with the actual image plane position of the “tree”. In the scenes shown in FIGS. 6A and 6B, the false peak lens position L3 is the position where the maximum focus evaluation value is detected, and the focus lens is located at the false peak lens position L3. When the drive 33 is driven, the “mountain” and “tree” are both out of focus, resulting in a blurred image. In this embodiment, as shown in FIGS. 6A, 6B, and 7, the focus lens 33 is driven from the infinity side to the close side, thereby widening the field angle (effective). Although an example in which the focal length is shortened) is exemplified, depending on the lens configuration, when the focus lens 33 is driven from the closest side to the infinity side, the angle of view becomes wider (the effective focal length becomes shorter). In some cases, the same applies.

  On the other hand, in this embodiment, in order to prevent the occurrence of such a problem, as shown in FIG. 8A, in addition to the focus detection area A1, the focus detection area A1 is included, and focus detection is performed. The extended area A2 includes a predetermined area wider than the area A1. In particular, in a scene similar to the scene shown in FIGS. 6A and 6B described above, as shown in FIG. 8A, the lens position of the focus lens 33 is expanded from the infinity side. “Tree” is captured in the area A2, and when the focus lens 33 is driven from the infinity side to the close side, the “tree” is always captured in the extended area A2. Yes (see FIG. 8B). In this case, as indicated by a solid line in FIG. 9, in the focus detection area A1, the false peak lens position L3 is detected as the lens position where the focus evaluation value is the maximum value. As indicated by a one-dot chain line in FIG. 9, in the extended area A2, no false peak is detected, and the lens position L2 corresponding to the image plane position of “tree” is detected as the lens position at which the focus evaluation value is the maximum value. The Rukoto. Therefore, in the present embodiment, when focus detection is performed by the contrast detection method, the extension area A2 is set, and the focus evaluation value data calculated from the luminance information in the extension area A2 is referred to, thereby the focus described above. This prevents a false peak from being detected as the angle of view of the lens 33 varies. The extension area A2 can be an area having the same center of gravity as the focus detection area A1 and a length ratio of one side that is about several percent larger than the focus detection area A1. In this case, when displaying via the liquid crystal driving circuit 25 and the electronic viewfinder 26, it is desirable to display only the area based on the focus detection area A1.

  Hereinafter, a specific operation example will be described with reference to the flowchart shown in FIG. In the operation example described below, the focus evaluation value is calculated based on the output of the imaging pixel 221 of the imaging element 22 while the focus lens 33 is search-driven from the infinity side to the near side in the camera shown in FIG. It is an operation example when performing focus detection by a contrast detection method based on the calculation. The following operation is executed by the camera control unit 21.

  First, in step S1, the camera control unit 21 outputs a drive signal to the focus lens drive motor 331 via the lens control unit 36, and moves the focus lens 33 to the search drive start position. Note that the search drive start position can be, for example, the infinity end in the present embodiment.

  Next, in step S2, the camera control unit 21 executes a process for starting search driving of the focus lens 33. Specifically, the camera control unit 21 outputs a drive signal to the focus lens drive motor 331 via the lens control unit 36, thereby moving the focus lens 33 from the infinity side to the close side at a predetermined speed. Let the drive do.

  When search driving of the focus lens 33 is started, the process proceeds to step S3. In step S3, the camera control unit 21 reads out the pixel output of the imaging pixel 221 (see FIG. 3) constituting the imaging element 22. Next, in step S4, the high frequency component of the read pixel output is extracted using a high frequency transmission filter, and the focus evaluation value is calculated by integrating the extracted high frequency components. The calculation of the focus evaluation value is performed for each of the two areas of the focus detection area A1 and the extension area A2 shown in FIG.

  Next, in step S5, the camera control unit 21 determines whether or not the focus lens 33 has moved to a predetermined search end. Note that, as the search end end, for example, in the present embodiment, the close end can be set. If the focus lens 33 has not moved to the search end, the process returns to step S3, and the pixel output of the imaging pixel 221 is read at a different lens position while driving the focus lens 33 from the infinity side to the close side ( Step S4) and calculation of the focus evaluation value (step S5) are repeatedly executed at predetermined intervals until the focus lens 33 moves to the end of search. If the focus lens 33 has moved to the search end, the process proceeds to step S6.

  In step S6, when the focus lens 33 is search-driven, the maximum focus evaluation value in the focus detection area A1 is obtained from the focus evaluation value calculated for the focus detection area A1, and the maximum focus evaluation value is obtained. The lens position P1 of the corresponding force lens 33 is detected. For example, in the examples shown in FIGS. 8A, 8B, and 9, the lens position L3 is detected as the lens position P1 corresponding to the maximum focus evaluation value. The lens position P1 is normally calculated as a value converted into the image plane position.

  In step S7, when the focus lens 33 is search-driven, the maximum focus evaluation value in the extension area A2 is obtained from the focus evaluation value calculated for the extension area A2, and corresponds to the maximum focus evaluation value. The lens position P2 of the force lens 33 is detected. For example, in the examples shown in FIGS. 8A, 8B, and 9, the lens position L2 is detected as the lens position P2 corresponding to the maximum focus evaluation value. The lens position P2 is normally calculated as a value converted into an image plane position, similarly to the lens position P1 described above.

  Next, in step S8, it is determined whether or not the maximum focus evaluation value in the focus detection area A1 calculated in step S6 described above is greater than or equal to a predetermined determination threshold value α. The determination threshold α is a threshold for determining whether or not the detected maximum focus evaluation value is obtained by detecting the subject position. For example, a low contrast such as blank paper is used. It is provided in order to avoid false focusing caused by an object, and can usually be set according to the sensitivity of the imaging element 22, the pixel output level of the imaging pixel 221 and the like. If the maximum focus evaluation value in the focus detection area A1 is greater than or equal to the determination threshold α, the process proceeds to step S9. On the other hand, if it is less than the determination threshold α, the process proceeds to step S13.

  In step S9, it corresponds to the lens position P1 corresponding to the maximum focus evaluation value of the focus detection area A1 calculated in step S6 and the maximum focus evaluation value of the extension area A2 calculated in step S7. An absolute value ΔP (ΔP = | P1−P2 |) of the difference from the lens position P2 is calculated, and the calculated absolute value ΔP of the difference between the lens position P1 and the lens position P2 is equal to or less than a predetermined first difference threshold value ΔP1. That is, it is determined whether or not ΔP ≦ ΔP1. When ΔP ≦ ΔP1, the process proceeds to step S10, and when ΔP ≦ ΔP1, the process proceeds to step S11. In addition, as 1st difference threshold-value (DELTA) P1, it can set to the range of about 1 to 2 times the depth of field, for example. That is, as the first difference threshold ΔP1, the lens position P1 corresponding to the maximum focus evaluation value of the focus detection area A1 and the lens position P2 corresponding to the maximum focus evaluation value of the expansion area A2 are substantially set. The value can be set so that it can be determined that the position corresponds to the same subject. Therefore, for example, as shown in FIGS. 11A and 11B, as shown in FIG. 11A, the focus lens 33 may be located on the infinity side as shown in FIG. As shown in (B), even when the lens position of the focus lens 33 is on the close side, the focus detection area A1 and the expansion area A2 capture only “mountains” as main subjects (that is, “trees”). ”Does not enter each of the areas A1 and A2), ΔP ≦ ΔP1, and thus the process proceeds to step S10. Alternatively, as shown in the scene examples shown in FIGS. 8A, 8 </ b> B, and 9, when a false focus peak due to a change in the angle of view caused by driving the focus lens 33 is detected, ΔP ≦ Since ΔP1 does not hold, the process proceeds to step S11.

  If it is determined in step S9 that the absolute value ΔP of the difference between the lens position P1 and the lens position P2 is equal to or smaller than the predetermined first difference threshold value ΔP1, the same subject is detected in the focus detection area A1 and the expansion area A2. It is determined that the focal position can be detected, and the lens position P1 is determined as a target drive position for performing focus drive. Then, the camera control unit 21 outputs a drive signal to the focus lens drive motor 331 via the lens control unit 36, and drives the focus lens 33 to the lens position P1. For example, in the scene example shown in FIGS. 11A and 11B, the lens position corresponding to the image plane position of “mountain” is detected as the lens position P1, and therefore the image plane position of “mountain”. A process of driving the focus lens 33 to the lens position corresponding to is executed.

  On the other hand, if it is determined in step S10 that the absolute value ΔP of the difference between the lens position P1 and the lens position P2 is greater than the predetermined first difference threshold value ΔP1, the process proceeds to step S11. It is determined whether or not the absolute value ΔP of the difference between the position P1 and the lens position P2 is equal to or smaller than a predetermined second difference threshold value ΔP2. That is, it is determined whether or not ΔP1 <ΔP ≦ ΔP2 is satisfied. The second difference threshold value ΔP2 can be set to about twice the first difference threshold value ΔP1, for example. If ΔP1 <ΔP ≦ ΔP2 is satisfied, the process proceeds to step S11. In step S11, the lens position P2 is determined as a target drive position for performing focus drive, and the camera control unit 21 performs lens control. A drive signal is output to the focus lens drive motor 331 via the unit 36, and the focus lens 33 is driven to the lens position P2. Alternatively, if ΔP1 <ΔP ≦ ΔP2 is not satisfied, the process proceeds to step S13.

  Here, in the scene example shown in FIGS. 8A and 8B, the focus detection area A1 is not focused on the “tree” at the start of the search drive of the focus lens 33, but the focus detection area A1. Due to the change in the angle of view accompanying the driving of the lens 33, “tree” enters the focus detection area A1, and as a result, a false peak is detected at the lens position L3 as shown in FIG. However, on the other hand, in the expansion area A2, since “tree” is within the range from the start of the search drive of the focus lens 33 to the end of the search drive, as shown in FIG. As the lens position P2 corresponding to the value, the lens position corresponding to the image plane position of “tree” can be appropriately detected. Therefore, in this embodiment, in such a case, the lens position P2 detected in the extended area A2 is determined as the focus position.

  However, on the other hand, the expansion area A2 is an area wider than the focus detection area A1 that is originally an area for performing focus detection, and further, in a shooting scene in which a change in magnification occurs during search driving. Since the focus position is searched using the focus evaluation value, it cannot be denied even when there is a problem in reliability. In particular, as the extended area A2, compared to the focus detection area A1, a relatively wide area is set. There is also a possibility that the peak position of the focus evaluation value is detected. Therefore, in the present embodiment, the lens position P2 detected in the extended area A2 is determined as the focus position only when the absolute value ΔP of the difference between the lens position P1 and the lens position P2 is equal to or smaller than the second difference threshold value ΔP2. To do.

  On the other hand, if it is determined in step S11 that ΔP1 <ΔP ≦ ΔP2 is not satisfied, it is further determined in step S8 described above that the maximum focus evaluation value in the focus detection area A1 is less than the determination threshold α. If YES in step S13, the flow advances to step S13 to perform out-of-focus processing. Specifically, the focus lens 33 is driven to a predetermined lens position, and the in-focus display is performed via the liquid crystal drive circuit 25 and the electronic viewfinder 26.

  The camera 1 according to the present embodiment operates as described above.

  In the present embodiment, in the shooting screen, in addition to the focus detection area A1, an extended area A2 that includes the focus detection area A1 and is wider than the focus detection area A1 is set. In these areas A1 and A2, focus areas are respectively set. Calculation of the evaluation value and detection of the lens positions P1 and P2 corresponding to the maximum value of the focus evaluation value are performed. If the absolute value ΔP of the difference between the lens position P1 and the lens position P2 is equal to or less than the predetermined first difference threshold value ΔP1, a false peak is generated due to the change in the angle of view caused by driving the focus lens 33. The lens position P1 detected in the focus detection area A1 is set as a target drive position for performing focus drive. Therefore, according to the present embodiment, it is possible to appropriately prevent the occurrence of blur due to the false peak due to the change in the angle of view due to the driving of the focus lens 33.

  In addition, according to the present embodiment, even if the absolute value ΔP of the difference between the lens position P1 and the lens position P2 is greater than the predetermined first difference threshold value ΔP1, it is equal to or less than the predetermined second difference threshold value ΔP2. In this case, the lens position P2 detected in the expansion area A2 is set as a target drive position for performing focus drive. In particular, as in the example of the scene shown in FIGS. 8A and 8B, in the extended area A2, “tree” is within the range from the start of the search drive of the focus lens 33 to the end of the search drive. 9, the lens position corresponding to the image plane position of “tree” can be appropriately detected as the lens position P2 corresponding to the maximum focus evaluation value, as shown in FIG. 9. In this case, since it is desirable to set the lens position P2 as a target drive position for performing focus drive, in this embodiment, the lens position P2 is set as a target drive position for performing focus drive. Thus, it is possible to increase the number of scenes that are in focus while effectively preventing false focusing, thereby improving convenience for the photographer. Moreover, it can suppress that it determines with being out-of-focus too much, and it can prevent effectively that this causes a troublesome photographer.

  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, the target for performing the focusing drive based on the absolute value ΔP of the difference between the lens position P1 and the lens position P2 regardless of the fluctuation ratio of the effective focal length due to the driving of the focus lens 33. Although the aspect of determining the drive position has been illustrated, for example, the process may be switched according to the variation rate of the effective focal length by driving the focus lens 33. Specifically, the camera control unit 21 calculates a focus evaluation value in the focus detection area A1 and the extended area A2 for each lens position during the search driving of the focus lens 33, and from the lens control unit 36, Get information on effective focal length for each lens position. Here, as shown in FIG. 12, the effective focal length does not change uniformly according to the change in the lens position of the focus lens 33, but has a characteristic that the fluctuation ratio also changes depending on the lens position. The occurrence of the false peak due to the change in the angle of view of the focus lens 33 has a characteristic that the possibility of occurrence becomes higher as the change in the angle of view increases.

  Therefore, in this embodiment, first, the lens position P1 corresponding to the maximum value of the focus evaluation value is detected for the focus detection area A1, and based on the information on the effective focal length for each lens position acquired from the lens control unit 36, The variation ratio of the effective focal length in the vicinity of the lens position P1 is calculated. Then, it is determined whether or not the change amount of the effective focal length with respect to the change amount of the position of the focus lens 33 in the vicinity of the lens position P1 is equal to or larger than a predetermined change amount threshold value, and is less than the predetermined change amount threshold value. Therefore, it is determined that the influence of the view angle variation is small, and the lens position P1 can be set as a target drive position for performing the focus drive. Alternatively, if it is equal to or greater than the predetermined change amount threshold value, it is determined that it is necessary to consider the influence of the change in the angle of view, and as described above, the expansion area A2 is set and the lens position P1 and the lens position P2 are set. The target drive position for performing the focus drive can be determined based on the absolute value ΔP of the difference. As described above, only when the influence of the angle of view is concerned, the focus state detection and the focus adjustment can be appropriately performed while reducing the calculation load by referring to the focus detection result in the extended area A2. . The information on the effective focal length for each lens position is, for example, a lens position indicating the relationship between the lens position in the optical axis L1 direction of the focus lens 33 stored in the lens memory 37 and the effective focal length at the lens position − It can be obtained by referring to the effective focal length table. Alternatively, instead of information on the effective focal length, flag information that can identify the driving direction of the focus lens 33 and the amount of change in the angle of view may be used as the optical characteristics of the lens barrel.

  In the above-described embodiment, the size of the extended area A2 may be changed based on the information about the effective focal length for each lens position acquired from the lens control unit 36. For example, the size of the expansion area A2 can be set according to the amount of change in the effective focal length when the focus lens 33 is driven from the infinity end to the close end. The larger the amount of change, the larger the size of the extended area A2, and the smaller the amount of change in the effective focal length, the smaller the size of the extended area A2, thereby causing the change in the effective focal length. It is possible to more appropriately perform focus detection and focus adjustment in accordance with the angle of view variation.

  Furthermore, in the above-described embodiment, the first difference threshold value ΔP1 is set to about 1 to 2 times the depth of field, and the second difference threshold value ΔP2 is set to about twice the first difference threshold value ΔP1. The values of ΔP1 and the second difference threshold value ΔP2 may be set based on the amount of change in the effective focal length when the focus lens 33 is driven from the infinity end to the close end. Specifically, the larger the change amount of the effective focal length, the larger the values of the first difference threshold value ΔP1 and the second difference threshold value ΔP2, and the smaller the change amount of the effective focal length, the first difference threshold value ΔP1 and the second difference threshold value ΔP2. The value of the two-difference threshold value ΔP2 can be set small, and thereby focus detection and focus adjustment according to the amount of change in the angle of view caused by the change in the effective focal length can be performed more appropriately.

  Alternatively, among the first difference threshold value ΔP1 and the second difference threshold value ΔP2, the first difference threshold value ΔP1 is fixed to a value of about 1 to 2 times the depth of field, and only the second difference threshold value ΔP2 is set to the focus lens 33. A configuration may be adopted in which the setting is made based on the change amount of the effective focal length when driving from the infinity end to the close end. In particular, in this case, by fixing the first difference threshold ΔP1 to a value of about 1 to 2 times the depth of field, the lens position P1 corresponding to the maximum focus evaluation value in the focus detection area A1, Only when it can be determined that the lens position P2 corresponding to the maximum focus evaluation value of the expansion area A2 is a position corresponding to the substantially same subject, the target for driving the lens position P1 to focus While it can be set as a position, for the extended area A2, focus detection and focus adjustment according to the amount of change in the angle of view caused by the change in the effective focal length can be performed. And focus adjustment can be performed.

  In the above-described embodiment, the case where there is only one focus detection area A1 has been described as an example. However, the camera 1 of the present embodiment is fixed as the focus detection area A1 via the operation unit 28. A mode in which only one focus detection area A1 such as a single area or a face recognition area is set, or an auto area mode in which a priority area is automatically selected from a plurality of focus detection areas A1 based on luminance information, a shooting mode, or the like However, in this case, the expansion area A2 is set only when the mode in which only one focus detection area A1 is set is selected, and the lens position P1 and the lens position are set. It is desirable that the target drive position for performing the focus drive is determined based on the absolute value ΔP of the difference from P2. In particular, in a mode in which focus detection is performed using a plurality of focus detection areas A1, there is a high possibility of being affected by fluctuations in the angle of view due to the large number of areas. Therefore, in such a case, an extended area When control with A2 set is performed, it may not be possible to appropriately perform focus state detection and focus adjustment. Therefore, in order to avoid such a problem, the expansion area A2 is set only when the mode in which only one focus detection area A1 is set is selected, and the absolute difference between the lens position P1 and the lens position P2 is set. It is desirable that the target drive position for performing the focus drive is determined based on the value ΔP.

  In the above-described embodiment, the camera 1 having the configuration shown in FIG. 1 has been described as an example. However, the present invention is not particularly limited to such a configuration. For example, the lens and the camera body are integrated. Of course, the present invention can also be applied to cameras having other configurations such as an integrated camera and a single-lens reflex camera with interchangeable lenses. Note that, in an integrated camera in which a lens and a camera body are integrated, the information on the effective focal length for each lens position described above is stored in, for example, a memory provided in the camera body. be able to.

DESCRIPTION OF SYMBOLS 1 ... Digital camera 2 ... Camera body 21 ... Camera control part 22 ... Imaging device 3 ... Lens barrel 32 ... Zoom lens 33 ... Focus lens 36 ... Lens control part 37 ... Lens memory

Claims (7)

An image sensor that captures an image by an optical system having a focus lens and outputs an image signal corresponding to the captured image;
A drive control unit that changes the focus state of the optical system by controlling the focus lens in the optical axis direction;
A first evaluation value calculation unit that calculates an evaluation value related to a contrast of an image by the optical system, based on the image signal output from the imaging element, for a first region in a photographing screen;
A first lens position calculation unit that calculates a position in the optical axis direction of the focus lens corresponding to the maximum value of the evaluation value calculated for the first region as a first lens position;
An evaluation value related to the contrast of an image by the optical system is calculated based on the image signal output from the imaging device for a second region in the photographing screen that includes the first region and is wider than the first region. A second evaluation value calculation unit;
A second lens position calculation unit that calculates a position in the optical axis direction of the focus lens corresponding to the maximum evaluation value calculated for the second region as a second lens position;
A first determination unit that determines whether or not a maximum evaluation value calculated for the first region is greater than or equal to a predetermined determination threshold;
When the maximum value of the evaluation value calculated for the first region is equal to or greater than the determination threshold, the difference between the first lens position and the second lens position is used to determine the first lens position or the second lens position. A focus adjustment apparatus comprising: a focusing lens position determination unit that determines a lens position as a focusing lens position. The focus adjustment apparatus according to claim 1,
The focusing lens position determining unit
When the difference between the first lens position and the second lens position is equal to or less than a predetermined first difference value, the first lens position is selected as a focusing lens position;
When the difference between the first lens position and the second lens position is greater than the first difference and less than or equal to a predetermined second difference value greater than the first difference value, the second lens position As the focus lens position, and
The focus adjusting apparatus according to claim 1, wherein when the difference between the first lens position and the second lens position is larger than the second difference value, it is determined as out of focus. The focusing apparatus according to claim 1 or 2,
An acquisition unit for acquiring information on an effective focal length of the optical system set for each position in the optical axis direction of the focus lens;
The focusing lens position determining unit
Only when the change amount of the effective focal length with respect to the change amount of the position of the focus lens in the optical axis direction in the vicinity of the first lens position is equal to or larger than a predetermined change amount threshold, the first lens position and the A focus adjustment apparatus that performs a process of determining the first lens position or the second lens position as a focusing lens position based on a difference from a second lens position. The focusing apparatus according to claim 1 or 2,
An acquisition unit for acquiring information on an effective focal length of the optical system set for each position in the optical axis direction of the focus lens;
The second evaluation value calculation unit sets the size of the second region in accordance with the amount of change in the effective focal length with respect to the amount of change in the position of the focus lens in the optical axis direction. Adjusting device. The focusing apparatus according to claim 2, wherein
An acquisition unit for acquiring information on an effective focal length of the optical system set for each position in the optical axis direction of the focus lens;
The focusing lens position determining unit
The focus adjustment apparatus, wherein the first difference value and the second difference value are set according to a change amount of the effective focal length with respect to a change amount of the position of the focus lens in the optical axis direction. In the focus adjustment apparatus in any one of Claims 1-5,
In the shooting screen, further comprising a mode setting unit capable of setting a plurality of the first region,
The focusing lens position determination unit is configured to detect the first lens position and the second lens position only when the mode setting unit sets the number of the first regions to one in the shooting screen. A focus adjustment device that executes a process of determining the first lens position or the second lens position as an in-focus lens position based on the difference between   An imaging device provided with the focus adjustment apparatus in any one of Claims 1-6.

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