JP2012247724A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of satisfactorily taking images.SOLUTION: The imaging apparatus includes: a rolling shutter type imaging device 22 in which plural pixels are disposed in a horizontal direction and a vertical direction and accumulation start time of charges at each pixel varies depending on the position of the pixel in the vertical direction; a focus detection section 21 that detects a focus state of an imaging lens in a focus detection area in an imaging screen on the basis of the output from an imaging device 22; a lens position detection section 21 that detects the position of a focus adjusting lens 32; an object position prediction section 21 that predicts the position in an optical axis direction of an object at a predetermined time; an accumulation start time calculation section 21 that calculates the accumulation start time of a pixel corresponding to the focus detection area; an object position calculation section 21 that calculates the position of the object in the optical axis direction at the accumulation start time of the pixel corresponding to the focus detection area as the object prediction position; and a drive section 36 that drives a focus adjusting lens on the basis of the object prediction position.

Description

  The present invention relates to an imaging apparatus.

  Conventionally, even if the moving subject moves in the optical axis direction after the shutter release button is fully pressed and before the exposure starts, the moving subject is focused at the start of exposure. An imaging apparatus that predicts the position of a moving subject at the start of exposure and controls the driving of a focus adjustment lens based on the prediction result is known (for example, Patent Document 1).

JP 2009-128611 A

  However, when a rolling shutter type image sensor is used, the charge accumulation start time in each pixel differs depending on the position of the pixel in the vertical direction in the image sensor. Since the shift of the charge accumulation start time for each pixel according to the pixel position is not taken into account, depending on the position of the focus detection area for performing focus detection, it may not be possible to capture an image focused on the moving subject. there were.

  The problem to be solved by the present invention is to provide an imaging apparatus capable of capturing a good image.

  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] In the imaging apparatus according to the present invention, a plurality of pixels are arranged two-dimensionally in the horizontal direction and the vertical direction, and the charge accumulation start time in each pixel varies depending on the position of the pixel in the vertical direction. A rolling shutter type image pickup device (22) and a focus detection unit that detects the focus state of the photographing lens including the focus adjustment lens (32) in the focus detection area in the image pickup screen based on the output from the image pickup device. (21), a lens position detection unit (35) for detecting the position of the focus adjustment lens, a subject position prediction unit (21) for predicting the position of the subject in the optical axis direction at a predetermined time, and the focus detection area An accumulation start time calculation unit (detecting the vertical position of the pixel corresponding to the image sensor in the image sensor and calculating the accumulation start time of the pixel corresponding to the focus detection area) 1) and a subject position calculation unit that calculates a position in the optical axis direction of the subject at the accumulation start time of the pixel corresponding to the focus detection area as a subject predicted position based on a prediction result by the subject position prediction unit. 21) and a drive unit (36) for driving the focus adjustment lens based on the predicted subject position calculated by the subject position calculation unit.

  [2] In the invention related to the imaging apparatus, the imaging element (22) includes a plurality of imaging pixels (221) arranged in a two-dimensional manner and a one-dimensional or two-dimensional configuration mixed in the imaging pixels. A plurality of focus detection pixels (222a, 222b) arranged in a shape, and the focus detection unit (21) is based on the output of the focus detection pixels and the amount of deviation of the image plane by the optical system Is used to calculate an evaluation value related to the contrast of the image by the optical system based on the focus detection of the phase difference detection method for detecting the focus state of the optical system and the output of the imaging pixel. Based on the evaluated value, focus detection can be performed by at least one of the contrast detection focus detections for detecting the focus state of the optical system.

  [3] In the invention related to the imaging apparatus, the image pickup apparatus further includes a determination unit (21) that determines whether or not the subject is stationary in the optical axis direction, and the drive unit (36) is a result of the determination by the determination unit. When it is determined that the subject is stationary in the optical axis direction, the focus adjustment lens driving process based on the predicted subject position may not be performed.

  [4] The invention according to the imaging apparatus further includes a movement speed calculation unit (21) that calculates a movement speed of the subject in the optical axis direction based on a prediction result by the subject position prediction unit (21), and the drive The unit moves the focus adjustment lens (32) while the charge is being accumulated in the pixel corresponding to the focus detection area after the accumulation start time of the pixel corresponding to the focus detection area. It can be configured to be driven at a constant speed according to the moving speed in the optical axis direction.

  [5] In the invention related to the imaging apparatus, the subject position calculation unit (21) corresponds to the focus detection area based on an exposure time of the pixel in addition to a prediction result by the subject position prediction unit (21). The position of the subject in the optical axis direction at a predetermined time while charge is being accumulated in the pixel to be calculated can be calculated as the subject predicted position.

  According to the present invention, a good image can be taken.

FIG. 1 is a block diagram showing a camera according to the present embodiment. FIG. 2 is a front view showing a focus detection area 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. 10 is a diagram for explaining a method of predicting the image plane position of the subject at the accumulation start time Ts. FIG. 11 is a diagram for explaining the operation of the camera according to the present embodiment.

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

<< First Embodiment >>
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. The adjustment of the aperture diameter by the diaphragm 34 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 37. Further, the set aperture diameter 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 imaging device 22 according to the present embodiment has a plurality of pixels arranged in a two-dimensional manner in the horizontal direction and the vertical direction on the imaging surface, and sequentially shutters each pixel row (scanning line) arranged in the horizontal direction. It is driven by a rolling shutter system that cuts off. As such an image sensor 22, for example, a CMOS image sensor can be used. The image sensor 22 receives a light beam from the subject, converts the received optical signal into an electrical signal, and sends the electrical signal 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 such a memory, either a removable card type memory or 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.

  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. Are output to the liquid crystal driving circuit 25 of the electronic viewfinder 26 and a memory (not shown) as a recording medium. 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 photographing optical system by the phase detection method and the focus state of the optical system by the contrast detection method based on the pixel data read from the image sensor 22. Do. A method for detecting the focus state will be described later.

  The operation unit 28 is a shutter release button and an input switch for the photographer to set various operation modes of the camera 1, and can switch between an autofocus mode and a manual focus mode. 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. In addition, although the optical black pixel area | region exists in the actual image pick-up element 22, in order to simplify description, description is abbreviate | omitted about FIG.

  As shown in FIG. 3, in the imaging element 22 of the present embodiment, a plurality of imaging pixels 221 are two-dimensionally arranged on the plane of the imaging surface in the horizontal direction and the vertical direction, and transmit the green wavelength region. A green pixel G having a color filter, 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. It is. 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, on the imaging surface of the imaging element 22, focus detection pixel rows 22 a to 22 e in which focus detection pixels 222 a and 222 b are arranged instead of the above-described imaging pixel 221 are provided. As shown in FIG. 3, one focus detection pixel column is configured by a plurality of focus detection pixels 222a and 222b being alternately arranged adjacent to each other in the horizontal direction. 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 22e shown in FIG. 2 are not limited to the illustrated positions, and may be any one, two, three, or four locations, and more than six locations. It can also be arranged at the position. In actual focus detection, the photographer manually operates the operation unit 28 to correspond to a plurality of the focus detection pixel rows 22a to 22e or a part of the focus detection pixel rows 22a to 22e. A desired focus detection area can also be selected from the focus detection areas.

  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. As shown in FIG. 3, these focus detection pixels 222a and 222b are alternately arranged adjacent to each other in the horizontal direction to constitute focus detection pixel rows 22a to 22e shown in FIG. FIG. 3 shows an example in which the focus detection pixel array is configured by 16 focus detection pixels 222a and 222b, but the number of focus detection pixels configuring the focus detection pixel array is not particularly limited.

  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 light beams that pass through a predetermined region (for example, 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 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 focal plane corresponding to the current focal plane (the position corresponding to the position of the microlens array on the planned focal plane). The deviation of the focal plane in the detection area), 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, for example, by extracting a high-frequency component of an image output from the imaging pixel 221 of the image sensor 22 using a high-frequency transmission filter and integrating the extracted high-frequency components to detect a focus voltage. It can also be obtained by extracting high-frequency components using two high-frequency transmission filters having different cutoff frequencies and integrating them to detect the focus voltage.

  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. Can be obtained by performing an operation such as interpolation using the focus evaluation value.

  Next, an operation example of the camera 1 according to the present embodiment will be described. FIG. 9 is a flowchart illustrating an operation example of the camera 1 according to the first embodiment.

  In step S101, the camera control unit 21 determines whether or not the shutter release button provided in the operation unit 28 is half-pressed (the first switch SW1 is turned on). If the shutter release button is half-pressed, the process proceeds to step S102. On the other hand, if the shutter release button is not half-pressed, the process waits in step S101.

  In step S102, the camera control unit 21 performs a defocus amount calculation process using a phase difference detection method. Specifically, first, the image sensor 22 receives light from the optical system, and the camera control unit 21 configures the focus detection pixels 222a constituting the five focus detection pixel rows 22a to 22e of the image sensor 22. , 222b, a pair of image data corresponding to the pair of images is read out. In this case, when a specific focus detection area is selected by a photographer's manual operation, only data from focus detection pixels corresponding to the focus detection area may be read. Then, the camera control unit 21 performs image shift detection calculation processing (correlation calculation processing) based on the read pair of image data, and images in the focus detection areas corresponding to the five focus detection pixel rows 22a to 22e. The shift amount is calculated, and the image shift amount is converted into a defocus amount.

In subsequent step S103, the camera control unit 21 drives the focus lens 32 according to the defocus amount based on the defocus amount calculated in step S102 and the current position of the focus lens 32 detected by the encoder 35. In this case, the image plane position at the lens position of the focus lens 32 after driving is detected as the image plane position of the subject. Then, the camera control unit 21 stores the detected image plane position of the subject in the memory of the camera control unit 21 in association with the time when the image plane position of the subject is detected. Here, FIG. 10 is a diagram illustrating an example of the history of the image plane position of the subject, and illustrates the history of the image plane position of the subject in a scene where the subject is moving from the infinity side to the close side. . In the example shown in FIG. 10, at time T1, is detected image plane position _{P T1} of the subject, then, at time T2, the image plane position _{P T2} of the object, near than the image plane position _{P T1} of the subject at time T1 Detected on the side. Similarly, the image plane positions P _T3 and P _T4 of the subject are detected at times T3 and T4, respectively. Then, the camera control unit 21 associates each detected image plane position with the time when the image plane position is detected and stores it in the memory of the camera control unit 21, as shown in FIG. The history of the image plane position of the subject along the series is stored in the memory of the camera control unit 21.

  In step S104, the camera control unit 21 calculates a lens driving amount for driving the focus lens 32 to the in-focus position based on the defocus amount calculated in step S102, and the calculated lens driving amount. Is sent to the focus lens drive motor 36 via the lens control unit 37. Thus, the focus lens driving motor 36 drives the focus lens 32 based on the calculated lens driving amount.

  In step S105, the camera control unit 21 determines whether or not the shutter release button is fully pressed (the second switch SW2 is turned on). When the second switch SW2 is on, the process proceeds to step S106, and when the second switch SW2 is not on, the process returns to step S101.

  In step S106, the camera control unit 21 determines whether the subject is moving in the optical axis direction based on the history of the image plane position of the subject obtained in step S103. If it is determined that the subject is moving in the optical axis direction, the process proceeds to step S107. On the other hand, if it is determined that the subject is not moving in the optical axis direction and the subject is stationary, step S107 is performed. Proceed to S111. In the present embodiment, for example, as illustrated in FIG. 10, the camera control unit 21 is configured when the image plane position of the subject is moving in a certain optical axis direction (the closest side in the example illustrated in FIG. 10). It can be determined that the subject is moving in the optical axis direction, and when the subject's image plane position has not moved, or the subject's image plane position has moved back and forth along the optical axis direction. However, when the image plane position of the subject has not moved in a certain optical axis direction, it can be determined that the subject is stationary.

  In step S107, the camera control unit 21 calculates the accumulation start time Ts at which charge accumulation is started in the pixels corresponding to the focus detection area. In the following, a method for calculating the accumulation start time Ts of the pixel corresponding to the focus detection area will be described with reference to FIG.

  FIG. 11 is a diagram for explaining the operation of the camera 1. FIG. 11B shows a shift in charge accumulation start time in each pixel in the image sensor 22 shown in FIG. . Note that the imaging element 22 illustrated in FIG. 11A detects the focus state of the optical system, and removes dark current noise from the effective pixel region including pixels for capturing an image and the output of the pixels in the effective pixel region. And an optical black pixel region composed of pixels for the purpose. In the example shown in FIG. 11, the shutter release button is fully pressed at time tS2, and a vertical synchronization signal is issued by the camera control unit 21 at time Tp. Thereby, exposure of the image sensor 22 is started from time Tp, and charge accumulation is started in order from the pixel located above the image sensor 22 toward the pixel located below the image sensor 22. Specifically, at time Tp, charge accumulation is started in the pixel of the optical black pixel region located at the top in the vertical direction among the pixels of the image sensor 22, and then, at time Ta, the pixel of the effective pixel region Charge accumulation is started in the pixel located at the top in the vertical direction. Then, in the pixels in the effective pixel region, charge accumulation is sequentially started, and the accumulation of the charge is completed for pixels for which a certain exposure time temp has elapsed from the start of charge accumulation. At time Tb, the charge accumulation is completed in the pixel located in the lowest vertical direction among the pixels in the effective pixel region, and further, at time Tc, the pixel in the image sensor 22 is located at the lowest in the vertical direction. Also in the pixels of the optical black pixel region that is positioned, the accumulation of electric charge is completed, and thus the exposure by the image sensor 22 is completed.

  The accumulation start time Ts of the pixel corresponding to the focus detection area thus differs depending on the position of the pixel in the vertical direction of the image sensor 22 and corresponds to the focus detection area among the charge accumulation start times of each pixel. This is the charge accumulation start time in the pixel. In the present embodiment, as shown in FIG. 11, the time at which the pixel located in the center in the vertical direction among the pixels corresponding to the focus detection area starts charge accumulation. And

The calculation method of the accumulation start time Ts is not particularly limited, but in the present embodiment, the accumulation start time Ts can be calculated based on the following formula (1).
Ts = Tp + tscan × (AFpos / Vsize) (1)
Here, as shown in FIG. 11B, tscan is a time Tp at which the vertical synchronization signal is generated, and charge accumulation is started in the pixel located at the top in the vertical direction among the pixels of the image sensor 22. To the time when charge accumulation is started in the pixel located at the lowest in the vertical direction among the pixels of the image sensor 22. Also, Vsize is the number of pixels in the vertical direction of the image sensor 22, and AFpos is the pixel in the vertical direction among the pixels corresponding to the focus detection area from the pixel located at the top in the vertical direction among the pixels of the image sensor 22. This is the number of pixels up to the pixel located at the center.

  In step S108, as shown in FIG. 11, the time from the time tS2 when the shutter release button is fully pressed to the accumulation start time Ts calculated in step S107 is displayed in the focus detection area by the camera control unit 21. Calculated as the accumulation delay time TR of the corresponding pixel.

In step S109, the camera control unit 21 predicts the image plane position of the subject at the accumulation start time Ts. Specifically, the camera control unit 21 calculates the image plane movement speed of the subject based on the history of the image plane position of the subject acquired in step S103, and calculates the image plane movement speed of the subject in step S108. Based on the calculated accumulation delay time TR, an image plane movement amount by which the subject moves during the accumulation delay time TR is calculated. The camera control unit 21 can predict the image plane position of the subject at the accumulation start time Ts based on the calculated image plane movement amount of the subject. For example, in the example shown in FIG. 10, the camera control unit 21, and the image plane moving amount of the subject in the storage delay time TR calculated, based on the latest position of the image plane P ₄ detected in step S103, accumulation start time The image plane position PTs of the subject at _Ts can be predicted.

  In step S110, the camera control unit 21 calculates a lens driving amount for driving the focus lens 32 to a lens position corresponding to the image plane position of the subject at the accumulation start time Ts predicted in step S109. The calculated lens driving amount is sent to the focus lens driving motor 36 via the lens control unit 37. Thus, the focus lens 32 is driven by the focus lens drive motor 36 to the lens position corresponding to the image plane position of the subject at the accumulation start time Ts based on the calculated lens drive amount.

  In step S111, exposure is started by the image sensor 22, and an image is captured. In this embodiment, as shown in FIG. 11, the exposure of the pixel corresponding to the focus detection area is started from the accumulation start time Ts, and the charge is accumulated for a predetermined exposure time temp from the accumulation start time Ts. Done. Then, the camera control unit 21 reads out image data corresponding to the accumulated charge from the image sensor 22, and the image data of the read image is stored in the memory 24.

  As described above, in the present embodiment, the image plane position of the subject at the accumulation start time Ts of the pixel corresponding to the focus detection area is predicted, and the focus lens 32 is moved to the lens position corresponding to the predicted image plane position of the subject. The image is taken by driving. Thereby, in the present embodiment, the subject moves in the optical axis direction during the accumulation delay time TR from when the shutter release button is fully pressed until the accumulation start time Ts of the pixel corresponding to the focus detection area. Even when the image plane position changes, an image in focus on the subject can be captured.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described. The second embodiment of the present invention predicts the subject image plane position at the accumulation start time Ts of the pixel corresponding to the focus detection area in the camera 1 of the first embodiment shown in FIG. After the focus lens 32 is driven to the lens position corresponding to the position, the charge is accumulated in the pixel corresponding to the focus detection area from the accumulation start time Ts according to the image plane moving speed of the subject. The configuration is the same as that of the first embodiment except that the focus lens 32 is driven at a constant speed.

  That is, in the second embodiment, as in the first embodiment, the image plane position of the subject at the accumulation start time Ts of the pixel corresponding to the focus detection area is predicted (step S109), and the predicted image plane position of the subject is set. The focus lens 32 is driven to the corresponding lens position (step S110). Then, the camera control unit 21 responds to the moving speed of the image plane of the subject from the accumulation start time Ts of the pixel corresponding to the focus detection area while charge is being accumulated in the pixel corresponding to the focus detection area. Then, an image is taken while driving the focus lens 32 at a constant speed (step S111). For example, in the example shown in FIG. 11, the camera control unit 21 drives the focus lens 32 to the lens position corresponding to the image plane position of the subject at the accumulation start time Ts, and then moves the focus lens 32 to the focus detection area. From the corresponding pixel accumulation start time Ts to the pixel accumulation end time Tg corresponding to the focus detection area, an image is captured while being driven at the image plane moving speed of the subject.

  As described above, in the second embodiment, while charge is accumulated in the pixel corresponding to the focus detection area, the image is generated while driving the focus lens 32 at a constant speed according to the image plane moving speed of the subject. Image. Thereby, in the second embodiment, in addition to the effects of the first embodiment, following the change in the image plane position of the subject while charge is being accumulated in the pixel corresponding to the focus detection area, Since an image can be captured, an image in focus on the subject can be captured more appropriately.

«Third embodiment»
Next, a third embodiment of the present invention will be described. The third embodiment of the present invention predicts the subject image plane position at a predetermined time within the exposure time of the pixel corresponding to the focus detection area in the camera 1 of the first embodiment shown in FIG. The configuration is the same as that of the first embodiment except that the focus lens 32 is driven to the lens position corresponding to the image plane position.

That is, in the third embodiment, the camera control unit 21 uses the pixel accumulation start time Ts corresponding to the focus detection area and the pixel exposure time temp within the pixel exposure time temp corresponding to the focus detection area. The predetermined time is calculated, and the image plane position of the subject at the calculated time is predicted (step S109). For example, in the example illustrated in FIG. 11, the camera control unit 21 determines the time when half of the exposure time temp of the pixel corresponding to the focus detection area has elapsed from the accumulation start time Ts of the pixel corresponding to the focus detection area. Te is calculated. Then, the camera control unit 21, as shown in FIG. 10, based on the history of the image plane position of the subject, to predict the image plane position P _Te of the object at time Te of the calculated the exposure time. Then, the lens position corresponding to the image plane position P _Te of the predicted subject, the focus lens 32 is driven (step S110), the lens position corresponding to the image plane position P _Te of the predicted subject captured image Is performed (step S111).

Thus, in the third embodiment, the image plane position of the subject at a predetermined time within the exposure time of the pixel corresponding to the focus detection area is predicted, and the focus lens is placed at the lens position corresponding to the predicted image plane position of the subject. 32 is driven to capture an image. Thus, in the third embodiment, for example, in the exposure time of the pixel corresponding to the focus detection area texp, image plane position of the object, even when moved to the image plane position P _Tg shown in FIG. 10, the focus lens 32, by driving the image plane position P _Te of the object at time Te within the exposure time of the pixels corresponding to the focus detection area texp, corresponding with the image plane position P _Tg of the object, the lens position of the focus lens Since the distance (P _Tg −P _Te ) with respect to the image plane position P _Te to be made can be made smaller than in the first embodiment, an image focused on the subject can be taken more appropriately.

  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 configuration in which the subject image plane position at the accumulation start time Ts of the pixel corresponding to the focus detection area is predicted, and the focus lens 32 is driven based on the predicted subject image plane position is illustrated. However, the present invention is not limited to this configuration. For example, the distance to the subject at the accumulation start time Ts of the pixel corresponding to the focus detection area is predicted, and the focus lens 32 is adjusted based on the predicted distance to the subject. It may be configured to drive.

  In the above-described embodiment, the image plane position of the subject is detected based on the defocus amount, and the subject at the accumulation start time Ts of the pixel corresponding to the focus detection area is detected based on the detected image plane position of the subject. Although the configuration for predicting the image plane position is exemplified, for example, the focus position is detected based on the focus evaluation value calculated by the contrast detection method, and the focus detection area is supported based on the history of the detected focus position The position of the subject at the pixel accumulation start time Ts may be predicted.

  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 28 ... Operation part 3 ... Lens barrel 32 ... Focus lens 36 ... Focus lens drive motor 37 ... Lens Control unit

Claims (5)

A plurality of pixels are arranged two-dimensionally in the horizontal direction and the vertical direction, and according to the position of the pixel in the vertical direction, an image pickup element of a rolling shutter system in which the charge accumulation start time in each pixel is different,
A focus detection unit that detects a focus state of a photographic lens including a focus adjustment lens in a focus detection area in an imaging screen based on an output from the imaging element;
A lens position detector for detecting the position of the focus adjustment lens;
A subject position prediction unit that predicts the position of the subject in the optical axis direction at a predetermined time;
An accumulation start time calculating unit that detects a vertical position of the pixel corresponding to the focus detection area in the image sensor and calculates the accumulation start time of the pixel corresponding to the focus detection area;
A subject position calculation unit that calculates a position of the subject in the optical axis direction at the accumulation start time of a pixel corresponding to the focus detection area as a subject predicted position based on a prediction result by the subject position prediction unit;
An image pickup apparatus comprising: a drive unit configured to drive the focus adjustment lens based on the subject predicted position calculated by the subject position calculation unit. The imaging apparatus according to claim 1,
The imaging element has a plurality of imaging pixels arranged in a two-dimensional manner, and a plurality of focus detection pixels mixed in the imaging pixels and arranged in a one-dimensional or two-dimensional manner,
The focus detection unit detects a shift amount of an image plane by the optical system based on an output of the focus detection pixel, and detects a focus state of a phase difference detection method for detecting a focus state of the optical system; and Among the focus detections of the contrast detection method, the evaluation value related to the contrast of the image by the optical system is calculated based on the output of the imaging pixel, and the focus state of the optical system is detected based on the calculated evaluation value. An image pickup apparatus capable of performing focus detection by at least one of the methods. The imaging apparatus according to claim 1, wherein:
A determination unit for determining whether or not the subject is stationary in the optical axis direction;
The drive unit does not perform the driving process of the focus adjustment lens based on the subject predicted position when it is determined that the subject is stationary in the optical axis direction as a result of the determination by the determination unit. An imaging apparatus characterized by the above. The imaging apparatus according to any one of claims 1 to 3,
Based on the prediction result by the subject position prediction unit, further comprising a movement speed calculation unit that calculates the movement speed of the subject in the optical axis direction,
After the accumulation start time of the pixel corresponding to the focus detection area, the driving unit moves the focus adjustment lens to the light of the subject while charge is being accumulated in the pixel corresponding to the focus detection area. An imaging apparatus that is driven at a constant speed according to a moving speed in an axial direction. The imaging apparatus according to any one of claims 1 to 4,
The subject position calculation unit is based on the exposure time of the pixel in addition to the prediction result by the subject position prediction unit, and at a predetermined time during which charge is accumulated in the pixel corresponding to the focus detection area. An imaging apparatus, wherein the position of the subject in the optical axis direction is calculated as the subject predicted position.

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