JP2013054120A - Focus detection device and focus adjustment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detection device in which an error in conversion from an image blur amount to a defocus amount is very small, even when the defocus amount is large and to provide a focus adjustment device.SOLUTION: The focus detection device includes a plurality of focus detection pixels receiving a pair of luminous fluxes passing through an exit pupil surface and outputting a pair of signals, image blur amount detection means detecting the image blur amounts of a pair of images by a pair of luminous fluxes, and a defocus amount calculation means calculating the defocus amount of an optical system by multiplying the image blur amount by a predetermined conversion coefficient. The defocus amount calculation means uses a first value as the value of the predetermined conversion coefficient, in a focusing close state and a second value smaller than the first value as the value of the predetermined conversion coefficient, in a large defocus state.

Description

  The present invention relates to a focus detection device and a focus adjustment device.

  A focus detection pixel having a microlens and a pair of photoelectric conversion units arranged behind the microlens is arranged on a predetermined focal plane of the photographing lens, and thereby a pair of focal points passing through an optical system (photographing optical system) including the photographing lens. A so-called pupil division type phase difference that generates a pair of image signals corresponding to a pair of images formed by the detection light beam and detects the focus adjustment state of the photographing lens by detecting an image shift amount between the pair of image signals. Detection type focus detection devices are known.

  In this type of focus detection device, a value obtained by dividing the exit pupil distance of the optical system by the distance between the centroids of a pair of regions through which the pair of focus detection light beams pass on the exit pupil of the optical system is used as a conversion coefficient. The defocus amount of the optical system is calculated by multiplying the image shift amount (phase difference) between the pair of image signals thus obtained by the conversion coefficient to detect the focus adjustment state (see, for example, Patent Document 1). .

JP 2008-268403 A

  However, in the above-described focus detection apparatus of this type, when the defocus amount is large, if the image shift amount is converted into the defocus amount as in the above-described prior art, a conversion error increases.

(1) A focus detection apparatus according to a first aspect receives a pair of light beams passing through an exit pupil plane of an optical system and outputs a pair of signals, and a correlation calculation process for the pair of signals. Thus, an image shift amount detection unit that detects an image shift amount of a pair of images due to a pair of light beams, and a defocus amount calculation unit that calculates a defocus amount of the optical system by multiplying the image shift amount by a predetermined conversion coefficient. Each of the light quantity distributions of the pair of light fluxes on the exit pupil plane is asymmetric with respect to the distribution center of gravity of each of the pair of light quantity distributions, and the defocus amount calculation means has a predetermined absolute value of the calculated defocus amount. The first value is used as the value of the predetermined conversion coefficient in the in-focus vicinity state that is less than the threshold value, and the first value as the predetermined conversion coefficient value in the large defocus state in which the absolute value is greater than or equal to the predetermined threshold value. From the value of Characterized by using a smaller second value.
(2) A focus adjustment apparatus according to a thirteenth aspect is the focus detection apparatus according to any one of the first to twelfth aspects, and the focus adjustment of the optical system according to the defocus amount calculated by the focus detection apparatus. And a focus adjusting means for performing the above.
(3) The focus detection apparatus according to claim 14 receives a pair of light beams passing through the exit pupil plane of the optical system, outputs a pair of signals, and correlation calculation processing for the pair of signals. Thus, an image shift amount detection unit that detects an image shift amount of a pair of images due to a pair of light beams, and a defocus amount calculation unit that calculates a defocus amount of the optical system by multiplying the image shift amount by a predetermined conversion coefficient. The defocus amount calculating means uses the first value as the value of the predetermined conversion coefficient in the near-focus state where the absolute value of the calculated defocus amount is less than the predetermined threshold, and the absolute value is a predetermined value. In the large defocus state that is equal to or greater than the threshold value, the second value smaller than the first value is used as the value of the predetermined conversion coefficient.

  According to the present invention, it is possible to provide a focus detection device and a focus adjustment device in which a conversion error from an image shift amount to a defocus amount is small even when the defocus amount is large.

It is a cross-sectional view showing a configuration of a digital still camera having a focus detection device and a focus adjustment device of an embodiment. It is a figure which shows the focus detection area on the imaging | photography screen set to the scheduled image formation surface of an interchangeable lens. It is a front view which shows the detailed structure of an image pick-up element. It is sectional drawing for demonstrating the state of the focus detection light beam which a focus detection pixel receives. It is sectional drawing for demonstrating the state of the focus detection light beam which a focus detection pixel receives. It is a figure which shows the relationship of a pair of focus detection light beam which arrives at each focus detection area from a pair of ranging pupil. It is the figure which showed how a pair of focus detection light flux was restrict | limited by the exit pupil of an interchangeable lens. It is a flowchart which shows operation | movement of a digital still camera. It is a figure for demonstrating an image shift detection calculation process. It is a flowchart which shows the detail of an image shift amount detection calculation process. It is the figure which showed the relationship between the actual defocus amount and the calculated defocus amount. It is a figure which shows an example which defined the conversion coefficient so that it might change continuously according to the absolute value of image shift amount. It is a figure which shows the relationship between a pair of focus detection light flux which arrives at the focus detection pixel arrange | positioned in the center of an imaging surface from a pair of ranging pupil. It is the figure which showed the light quantity distribution shape of a pair of blur image at the time of large defocusing. FIG. 6 is a conceptual diagram when a pair of blurred images are relatively shifted and the barycentric lines passing through the barycentric positions are matched. It is a conceptual diagram at the time of a relative shift of a pair of blurred images so that the correlation amount is minimized. It is the figure which showed the light quantity distribution shape of a pair of blur image in case a defocus amount is comparatively small. FIG. 6 is a conceptual diagram when a pair of blurred images are relatively shifted and the barycentric lines passing through the barycentric positions are matched. It is a figure which shows the shape of a pair of ranging pupil distribution when the F value of an optical system is comparatively large. It is a figure which shows the shape of a pair of ranging pupil distribution in case a pair of focus detection light flux is restrict | limited nonuniformly by vignetting. It is a front view which shows the detailed structure of an image pick-up element.

  As an imaging apparatus having a focus detection apparatus and a focus adjustment apparatus according to an embodiment of the present invention, a lens interchangeable digital still camera will be described as an example. FIG. 1 is a cross-sectional view showing a configuration of a digital still camera having a focus detection device and a focus adjustment device according to an embodiment. A digital still camera 201 according to the present embodiment includes an interchangeable lens 202 and a camera body 203, and the interchangeable lens 202 is attached to the camera body 203 via a mount unit 204. An interchangeable lens 202 having various photographing optical systems can be attached to the camera body 203 via a mount unit 204.

  The interchangeable lens 202 includes a lens 209, a zooming lens 208, a focusing lens 210, a diaphragm 211, a lens drive control device 206, and the like. The lens drive control device 206 includes a microcomputer (not shown), a memory, a drive control circuit, and the like, and adjusts the focus of the focusing lens 210, drive control for adjusting the aperture diameter of the stop 211, zooming lens 208, and focusing lens. 210 and the state of the diaphragm 211 are detected. In addition, transmission of lens information and reception of camera information (defocus amount, aperture value, etc.) are performed by communication with a body drive control device 214 described later. The aperture 211 forms an aperture having a variable aperture diameter at the center of the optical axis in order to adjust the amount of light and the amount of blur.

  The camera body 203 includes an image sensor 212, a body drive control device 214, a liquid crystal display element drive circuit 215, a liquid crystal display element 216, an eyepiece lens 217, a memory card 219, and the like. In the imaging element 212, imaging pixels are two-dimensionally arranged, and focus detection pixels are incorporated in portions corresponding to focus detection positions (focus detection areas). Details of the image sensor 212 will be described later.

  The body drive control device 214 includes a microcomputer, a memory, a drive control circuit, and the like. The body drive control device 214 repeatedly performs exposure control of the image sensor 212 and readout of the pixel signal from the image sensor 212, focus detection calculation based on the pixel signal of the focus detection pixel, and focus adjustment of the interchangeable lens 202, Processing and recording of image signals, camera operation control, etc. The body drive control device 214 communicates with the lens drive control device 206 via the electrical contact 213 to receive lens information and send camera information.

  The liquid crystal display element 216 functions as an electric view finder (EVF). The liquid crystal display element driving circuit 215 displays a through image on the liquid crystal display element 216 based on the image data read from the image sensor 212, and the photographer can observe the through image through the eyepiece 217. The memory card 219 is an image storage that stores image data captured by the image sensor 212.

  A subject image is formed on the light receiving surface of the image sensor 212 by the light beam that has passed through the interchangeable lens 202. This subject image is photoelectrically converted by the image sensor 212, and the pixel signal (imaging signal) of the imaging pixel and the pixel signal (focus detection signal) of the focus detection pixel are sent to the body drive control device 214.

  As will be described later with reference to FIG. 8, the body drive control device 214 detects and detects the image shift amount of the pair of image data based on the pixel signal (focus detection signal) from the focus detection pixel of the image sensor 212. A defocus amount is calculated based on the image shift amount. That is, the focus detection device in the present embodiment includes at least an image sensor 212 that outputs a focus detection signal, and a body drive control device 214 that performs image shift amount detection and defocus amount calculation. When the body drive control device 214 detects the focus adjustment state of the interchangeable lens 202 based on the defocus amount, and determines that the focus adjustment state is not close to the in-focus state, the body drive control device 214 sends this defocus amount to the lens drive control device 206. The focus is adjusted by driving the focusing lens 210 and the aperture 211 to 206. That is, the focus adjustment apparatus in the present embodiment includes the above-described focus detection apparatus, and the body drive control device 214 of the focus detection apparatus included in the focus adjustment apparatus further performs focus adjustment. The body drive control device 214 processes the pixel signal from the image sensor 212 to generate image data, stores it in the memory card 219, and drives the through image signal read from the image sensor 212 to drive the liquid crystal display element. The image is sent to the circuit 215 and the through image is displayed on the liquid crystal display element 216. Further, the body drive control device 214 sends aperture control information to the lens drive control device 206 to control the aperture of the aperture 211.

  The lens drive controller 206 updates the lens information according to the focusing state, zooming state, aperture setting state, aperture opening F value, and the like. Specifically, the positions of the zooming lens 208 and the focusing lens 210 and the aperture value of the aperture 211 are detected, and lens information is calculated according to these lens positions and aperture values, or prepared in advance. Lens information corresponding to the lens position and aperture value is selected from the look-up table.

  The lens drive control device 206 calculates a lens drive amount based on the received defocus amount, and drives the focusing lens 210 to the in-focus position according to the lens drive amount. Further, the lens drive control device 206 drives the diaphragm 211 in accordance with the received diaphragm value.

  FIG. 2 is a diagram illustrating an example of a focus detection area (focus detection position) on a shooting screen defined on the planned imaging plane of the interchangeable lens 202. The focus detection area shown in FIG. 2 shows an example of a region where an image is sampled on the shooting screen when a focus detection pixel array on the image sensor 212 described later performs focus detection. In this example, focus detection areas 101, 102, and 103 are arranged at the center and three locations on the top and bottom of the rectangular shooting screen 100. In the focus detection areas 101, 102, and 103, the focus detection pixels are linearly arranged so as to correspond to the longitudinal direction of the focus detection area indicated by a rectangle, that is, the vertical direction (vertical direction) of the photographing screen 100 in FIG. The

  FIG. 3 is a front view showing a detailed configuration of the image sensor 212, and shows an enlarged vicinity of a region on the image sensor 212 corresponding to the focus detection areas 101, 102, and 103 in FIG. The imaging pixels 310 are densely arranged in a two-dimensional square lattice pattern on the imaging device 212, and focus detection pixels 312 and 313 for focus detection are arranged in a vertical direction (positions corresponding to the focus detection areas 101, 102, and 103). The focus detection pixel columns are formed alternately and adjacently on a straight line in the vertical direction.

  The imaging pixel 310 includes the microlens 10, the photoelectric conversion unit 11 whose light receiving area is limited to a square by a light shielding mask (not shown), and a color filter (not shown). The color filters include three types of red (R), green (G), and blue (B), and have spectral sensitivity characteristics corresponding to the respective colors. In the image pickup device 212, image pickup pixels 310 having respective color filters are arranged in a Bayer array.

  The focus detection pixels 312 and 313 are provided with a white filter (not shown) that transmits all visible light in order to perform focus detection for all colors. The white filter has a spectral sensitivity characteristic that is the sum of the spectral sensitivity characteristics of the green pixel, red pixel, and blue pixel, and the light wavelength region exhibiting high sensitivity is in each color for each of the green pixel, red pixel, and blue pixel. It covers the optical wavelength region where the filter shows high sensitivity.

  The focus detection pixel 312 includes a microlens 10, a photoelectric conversion unit 12 in which a light receiving region is limited to a rectangle (substantially upper half when a square is divided into two equal parts by a horizontal line) by a light shielding mask (not shown), and a white filter (not shown). (Illustrated). The focus detection pixel 313 includes a microlens 10, a photoelectric conversion unit 13 whose light receiving area is limited to a rectangle (substantially lower half when a square is divided into two equal parts by a horizontal line), and a white filter (not shown). (Illustrated). When the focus detection pixel 312 and the focus detection pixel 313 are displayed so as to overlap each other with the microlens 10 as a reference, the pair of photoelectric conversion units 12 and 13 whose light receiving areas are limited by the light shielding mask are arranged in the vertical direction.

  FIG. 4 shows focus detection pixels 312 and 313 that form focus detection pixel rows arranged in the image sensor 212 corresponding to the focus detection area 101 extending in the vertical direction (longitudinal direction) in the vicinity of the center of the photographing screen 100. It is sectional drawing for demonstrating the state of the focus detection light beam which light-receives.

  In FIG. 4, the optical axis 91 of the interchangeable lens, the microlenses 10a to 10d, the photoelectric conversion units 12a, 12b, 13a, and 13b, the focus detection pixels 312a, 312b, 313a, and 313b, whose light receiving areas are limited by the light shielding mask opening, Focus detection light beams 72, 73, 82 and 83 are shown.

  The photoelectric conversion units 12 and 13 of all the focus detection pixels 312 and 313 arranged on the image sensor 212 receive the light flux that has passed through the light shielding mask opening disposed in the vicinity of the photoelectric conversion units 12 and 13. The shape of the light-shielding mask opening arranged close to the photoelectric conversion unit 12 of each focus detection pixel 312 is the focus detection on the distance measurement pupil plane 90 separated from the microlens 10 by the distance measurement pupil distance d by the microlens 10. Projection is performed on a region 92 common to all of the pixels 312. Similarly, the shape of the light-shielding mask opening disposed in the vicinity of the photoelectric conversion unit 13 of each focus detection pixel 313 is a focus on the distance measurement pupil plane 90 that is separated from the microlens 10 by the distance measurement pupil distance d by the microlens 10. Projection is performed on a region 93 common to all the detection pixels 313. The distance measuring pupil plane 90 is defined at substantially the same position as the exit pupil plane of the optical system included in the interchangeable lens 202. That is, the distance measurement pupil distance d from the microlens 10 to the distance measurement pupil plane 90 is substantially equal to the exit pupil distance from the microlens 10 to the exit pupil of the optical system. A pair of regions 92 and 93 on the distance measuring pupil plane 90 is called a distance measuring pupil.

  The focus detection pixels 312a and 312b receive focus detection light beams 72 and 82 that pass through the distance measuring pupil 92 and the microlenses 10a and 10c of the respective imaging pixels by the photoelectric conversion units 12a and 12b, and focus detection light beams 72 and 82 are received. To output a signal corresponding to the intensity of the image formed on each of the microlenses 10a and 10c. The focus detection pixels 313a and 313b receive the focus detection light beams 73 and 83 passing through the distance measuring pupil 93 and the microlenses 10b and 10d of the respective image pickup pixels by the photoelectric conversion units 13a and 13b. 83 outputs a signal corresponding to the intensity of the image formed on each of the microlenses 10b and 10d.

  In FIG. 4, four focus detection pixels (pixels 312 a, 313 a, 312 b, and 313 b) adjacent to the photographing optical axis 91 are schematically illustrated, but are arranged in the image sensor 212 corresponding to the focus detection area 101. Also in the other focus detection pixels included in the focus detection pixel row, the photoelectric conversion units receive the light fluxes that arrive at the microlenses from the corresponding distance measurement pupils 92 and 93, respectively. The arrangement direction of the focus detection pixels coincides with the arrangement direction of the pair of distance measuring pupils, that is, the arrangement direction of the pair of photoelectric conversion units.

  FIG. 5 shows focus detection pixels 312 and 313 that form focus detection pixel rows arranged in the image sensor 212 corresponding to the focus detection area 102 extending in the vertical direction (longitudinal direction) in the peripheral region of the shooting screen 100. It is a figure for demonstrating the state of the focus detection light beam which light-receives.

  FIG. 5 shows microlenses 10e, 10f, 10g, and 10h, photoelectric conversion units 12c, 12d, 13c, and 13d in which a light receiving region is limited by a light shielding mask opening, focus detection pixels 312c, 312d, 313c, and 313d, focus detection light fluxes. 172, 173, 182, and 183 are shown.

  The focus detection pixels 312c and 312d receive the focus detection light beams 172 and 182 that pass through the distance measuring pupil 92 and the microlenses 10e and 10g of the imaging pixels by the photoelectric conversion units 12c and 12d, and focus detection light beams 172 and 182, respectively. To output a signal corresponding to the intensity of the image formed on each of the microlenses 10e and 10g. The focus detection pixels 313c and 313d receive the focus detection light beams 173 and 183 that pass through the distance measuring pupil 93 and the microlenses 10f and 10h of the imaging pixels by the photoelectric conversion units 13c and 13d, respectively. A signal corresponding to the intensity of the image formed on each of the microlenses 10f and 10h is output by 183.

  In FIG. 5, adjacent four focus detection pixels (pixels 312 a, 313 a, 312 b, and 313 b) in the focus detection area 102 are schematically illustrated, but other focus detection pixels included in the focus detection area 102 are illustrated. In addition, the photoelectric conversion units receive the light fluxes that arrive at the microlenses from the corresponding distance measurement pupils 92 and 93, respectively.

4 and 5, the pair of distance measurement pupils 92 and 93 are arranged symmetrically with respect to the optical axis 91. When the focus detection area is arranged around the photographing screen as shown in FIG. 5, the light beam just passing through the intermediate point C ₀ between the pair of distance measurement pupils 92 and 93 is the distance from the microlens 10 to the distance measurement pupil distance d. It intersects the optical axis 91 only at the intermediate point C _{0 at the} position.

  The arrangement of the focus detection pixels corresponding to the focus detection area 103 is the same as the arrangement of the focus detection pixels corresponding to the focus detection area 102, and the focus detection pixels corresponding to the focus detection area 103 are also the ranging pupil 92. , 93 is received.

  As described above, in the region corresponding to the focus detection areas 101 to 103, a large number of the pair of focus detection pixels 312 and 313 are arranged alternately and linearly. A pair of focus detections that respectively pass through the distance measuring pupil 92 and the distance measuring pupil 93 by collecting the outputs of the photoelectric conversion units of the focus detection pixels into a pair of output groups corresponding to the distance measuring pupil 92 and the distance measuring pupil 93. Information on the intensity distribution of a pair of images formed by the light beam on the vertical focus detection pixel array is obtained. By applying an image shift detection calculation process (correlation calculation process, phase difference detection process), which will be described later, to this information, an image shift amount of a pair of images is detected by a so-called pupil division type phase difference detection method. Further, by performing a conversion calculation using a conversion coefficient corresponding to the proportional relationship between the distance between the center of gravity of the pair of distance measurement pupils and the distance measurement pupil distance to the image shift amount, the focus adjustment state (defocusing) in each focus detection area is performed. Amount) is calculated.

  FIG. 6 is a diagram illustrating a relationship between a pair of focus detection light beams that arrive at each focus detection area from a pair of distance measurement pupils. 4 and 5, the focus detection areas 101A, 102A, and 103A corresponding to the focus detection areas 101, 102, and 103A have a pair of focus detection light beams that pass through the pair of distance measurement pupils 92 and 93. An image is formed. The focus detection pixels arranged corresponding to the focus detection areas 101A, 102A, and 103A output pixel signals corresponding to the pair of images. The focus detection light beam 272 passing through the distance measurement pupil 92 and the focus detection light beam 273 passing through the distance measurement pupil 93 form a pair of images in the focus detection region 101A. The focus detection light beam 282 passing through the distance measurement pupil 92 and the focus detection light beam 283 passing through the distance measurement pupil 93 form a pair of images in the focus detection region 102A. The focus detection light beam 292 passing through the distance measurement pupil 92 and the focus detection light beam 293 passing through the distance measurement pupil 93 form a pair of images in the focus detection region 103A.

  As described above, the distance measuring pupil plane 90 is normally defined at substantially the same position as the exit pupil plane of the optical system included in the interchangeable lens 202. However, the position of the distance measuring pupil plane 90 and the exit pupil plane are not limited. Due to the difference in position, vignetting may occur in the pair of focus detection light beams. FIG. 7 is a diagram corresponding to FIG. 6, where the exit pupil distance dn from the image sensor 212 to the exit pupil 95 of the interchangeable lens is shorter than the distance measurement pupil distance d, and the exit pupil distance df is the distance measurement pupil distance d. In a longer case, each pair of focus detection light fluxes (272, 273), (282, 283), (292, 293) arriving at the focus detection regions 101A, 102A, 103A is the aperture due to the exit pupil 95 of the interchangeable lens. It is a figure showing how it was restricted by erosion and vignetting. The exit pupil 95 of the interchangeable lens shown in FIG. 7 is an exit pupil when the diaphragm aperture is viewed from the image sensor side.

  When the exit pupil 95 of the interchangeable lens is an exit pupil 95A at a distance d from the image sensor 212, the pair of distance measurement pupils 92 and 93 is limited to a circular exit pupil centered on the optical axis. Therefore, each pair of focus detection light beams (272, 273), (282, 283), (292, 293) arriving at the focus detection regions 101A, 102A, 103A is limited symmetrically with respect to the optical axis. .

  In FIG. 7, when the exit pupil 95 of the interchangeable lens is the exit pupil 95B located at the exit pupil distance dn from the image sensor 212, the pair of focus detection light beams (272, 273) arriving at the focus detection region 101A are on the optical axis. The pair of focus detection light fluxes (282, 283) and (292, 293) arriving at the focus detection regions 102A and 103A are asymmetric with respect to the optical axis. It is limited to be asymmetric by the symmetric exit pupil 95B.

  FIG. 8 is a flowchart showing the operation of the digital still camera 201 shown in FIG. Each processing step shown in FIG. 8 is executed by the body drive control device 214. When the power of the digital still camera 201 is turned on in step S100, the body drive control device 214 starts the operation after step S110. In step S <b> 110, the image pickup pixel data is read out and displayed on the liquid crystal display element 216. In the following step S120, a pair of image data (a pair of signals, a pair of signals) output from the pair of photoelectric conversion units that receive the pair of focus detections that pass through the pair of distance measurement pupils from the focus detection pixel array. Read a pair of data strings). Note that the focus detection area is selected by the photographer using an area selection switch (not shown).

  In step S130, the body drive control device 214 performs an image shift detection calculation process (difference type correlation calculation process) to be described later on the read pair of image data, and calculates an image shift amount. In step S135, the body drive control device 214 multiplies the image shift amount by a conversion coefficient to convert it to a defocus amount. Details of the conversion process will be described later.

  In step S140, the body drive control device 214 checks whether or not it is close to focusing, that is, whether or not the calculated absolute value of the defocus amount is within a predetermined value. If it is determined that the focus is not close, the process proceeds to step S150, where the body drive control device 214 transmits the defocus amount to the lens drive control device 206, and drives the focusing lens 210 of the interchangeable lens 202 to the focus position. Return to step S110 to repeat the above-described operation. Even when focus detection is impossible, the process branches to this step, and the body drive control device 214 transmits a scan drive command to the lens drive control device 206, and scans the focusing lens 210 of the interchangeable lens 202 from infinity to the nearest. Let Then, it returns to step S110 and repeats the operation | movement mentioned above.

  On the other hand, if it is determined in step S140 that the focus is close to the in-focus state, the process proceeds to step S160, and the body drive control device 214 determines whether or not a shutter release has been performed by operating a shutter button (not shown). If it is determined that the shutter release has not been performed, the process returns to step S110 and the above-described operation is repeated. When the shutter release is performed, the process proceeds to step S170, and the body drive control device 214 transmits an aperture adjustment command to the lens drive control device 206, and controls the aperture value of the interchangeable lens 202 to the control F value (F set by the photographer). Value or automatically set F value).

  When the aperture control is completed, the body drive control device 214 causes the imaging device 212 to perform an imaging operation, and reads image data from the imaging pixels of the imaging device 212 and all focus detection pixels. In step S180, the body drive control device 214 generates pixel data at each pixel position in the focus detection pixel row by pixel interpolation based on pixel data of imaging pixels around the focus detection pixel. In subsequent step S190, the body drive control device 214 stores the image data including the pixel data of the imaging pixel and the pixel data generated by the pixel interpolation in the memory card 219, and returns to step S110 to repeat the above-described operation.

  Next, details of a general image shift detection calculation process (difference type correlation calculation process) used in step S130 of FIG. 8 will be described.

A pair of signals read from the pair of focus detection pixel columns, that is, a pair of data columns (data of the focus detection pixel 313: A1 _{1 to} A1 _M , data of the focus detection pixel 314: A2 _{1 to} A2 _M , M is data The correlation amount C (k) is calculated using the following correlation calculation formula (1). In the Σ operation in Expression (1), the difference between the data of the pair of focus detection pixels 313 and 314 is accumulated by changing the value of the variable n to relatively displace the pair of data strings. The range of the value of the variable n is data A1 _n , A1 according to the relative displacement amount of the pair of data strings when the difference between the data of the pair of focus detection pixels 313 and 314 is accumulated, that is, the phase difference k. It is limited to a range where _{n + 1} , A2 _{n + k} and A2 _{n + 1 + k} exist. The phase difference k is an integer and is a relative phase difference with the data interval of the data string as a unit. As shown in Expression (1), the correlation amount C (k) changes according to the phase difference k.
C (k) = Σ | A1 _n −A2 _{n + k} | (1)

  Since the operation represented by the equation (1) is an operation for accumulating the absolute values of the differences, the correlation operation including the subtraction represented by the equation (1) is called a differential correlation operation. In general, in the differential correlation calculation, the correlation amount C (k) has a characteristic that takes a minimum value in the phase difference k when the correlation degree of the pair of data strings corresponding to the degree of coincidence of the pair of images shows the maximum value. . The smaller the correlation amount C (k), the higher the degree of correlation.

  As shown in FIG. 9A, the calculation result of Expression (1) is a discrete correlation amount in the phase difference (k = kj = 2 in FIG. 9A) when the correlation between the pair of data strings is high. C (k) is minimized.

A phase difference ks that gives a minimum value C (ks) of a continuous correlation amount is obtained using a three-point interpolation method according to equations (2) to (5).
ks = kj + D / SLOP (2)
C (ks) = C (kj) − | D | (3)
D = {C (kj−1) −C (kj + 1)} / 2 (4)
SLOP = MAX {C (kj + 1) -C (kj), C (kj-1) -C (kj)} (5)

  Whether or not the phase difference ks calculated by the equation (2) is reliable is determined as follows.

  As shown in FIG. 9B, when the degree of correlation between the pair of data strings is low, the value of the interpolated correlation minimum value C (ks) increases. Therefore, when the minimum value C (ks) of the correlation amount is equal to or greater than a predetermined threshold, it is determined that the reliability of the calculated phase difference ks is low, and the calculated phase difference ks is canceled.

  Alternatively, in order to normalize the minimum value C (ks) of the correlation amount with the contrast of the pair of data strings, a division value obtained by dividing the minimum value C (ks) of the correlation amount by SLOP which is a value proportional to the contrast is obtained. If the division value is equal to or greater than a predetermined value, it is determined that the reliability of the calculated phase difference ks is low, and the calculated phase difference ks is canceled.

  Alternatively, when the SLOP that is proportional to the contrast is equal to or less than the predetermined value, it is determined that the subject has low contrast and the reliability of the calculated phase difference ks is low, and the calculated phase difference ks is canceled. .

  As shown in FIG. 9C, when the correlation degree of the pair of data strings is low and there is no drop in the correlation amount C (k) between the shift ranges kmin to kmax of the phase difference k, the minimum value of the correlation amount C (ks) cannot be obtained. In such a case, it is determined that focus detection is impossible.

Note that the differential correlation calculation formula is not limited to the formula (1), and for example, the following calculation formula disclosed in JP 2007-333720 A may be used.
C (k) = Σ | A1 n · A2 n + 1 + k -A2 n + k · A1 n + 1 | ··· (6)

When it is determined that the calculated phase difference ks is reliable, the phase difference ks is converted into the above-described image shift amount shft representing the phase difference between the pair of images according to the equation (7). In this way, the body drive control device 214 detects the image shift amount shft. In equation (7), the coefficient PY is twice the pixel pitch.
shft = PY · ks (7)

  The above is a flowchart showing details of the image shift amount detection calculation processing in step S130 of FIG. Next, FIG. 10 showing details of the conversion process (defocus amount calculation process) by the body drive control device 214 from the image shift amount to the defocus amount in step S135 in FIG. 8 will be described.

In step S200 of FIG. 10, the body drive control device 214 multiplies the image shift amount shft by the conversion coefficient Kd1 according to equation (8) to obtain the distance between the planned focal plane of the optical system and the imaging plane of the optical system. Conversion (calculation) into a corresponding defocus amount def.
def = Kd1 · shft (8)

  The conversion coefficient Kd1 is a conversion coefficient for in-focus vicinity, and corresponds to the average opening angle of a pair of light beams received by the focus detection pixel (the opening angle of light beams passing through the center of gravity of the pair of light beams). Since the average opening angle of the pair of light beams received by the focus detection pixel changes according to the F value of the optical system (imaging optical system), the conversion coefficient Kd1 is also different from that of the lens drive control device 206 by the body drive control device 214. It changes in accordance with lens information (F value when focus detection pixel data is read) acquired by communication.

In step S210, the body drive control device 214 checks whether or not the absolute value of the defocus amount calculated by the equation (8) is greater than or equal to a predetermined threshold value Dt1, and if not, the body drive control device 214 returns to FIG. The defocus amount calculation process shown is exited. When the absolute value of the defocus amount calculated by the equation (8) is equal to or greater than the predetermined threshold value Dt1, the image shift amount shft is multiplied by the conversion coefficient Kd2 and converted to the defocus amount def according to the equation (9). Then, the process exits the defocus amount calculation process shown in FIG.
def = Kd2 · shft (9)

  Note that the conversion coefficient Kd2 is a conversion coefficient for large defocus and has a value equal to or less than the conversion coefficient Kd1. The conversion coefficient Kd2 also changes according to the lens information (F value when the focus detection pixel data is read) acquired by the body drive control device 214 through communication with the lens drive control device 206.

  That is, in the operation flow of FIG. 10, when the focus adjustment state of the photographic optical system is included in the range near the in-focus state, the image shift amount shft is multiplied by the conversion coefficient Kd1 having a relatively large value to convert it to the defocus amount def. In other cases (when the focus adjustment state of the photographic optical system is outside the range near the in-focus state), the image shift amount shft is multiplied by the conversion coefficient Kd2 having a relatively small value to convert it to the defocus amount def. As a result, the detection error of the defocus amount is reduced. When the absolute value of the defocus amount is less than the predetermined threshold value Dt1, it is determined that the focus adjustment state of the photographing optical system is included in the range near the in-focus state.

  In the operation flow of FIG. 10, the predetermined threshold value Dt1 may be changed according to the F value of the optical system (the larger the F value, the larger the threshold value, so that Dt1 / F becomes substantially constant). .

  In the operation flow of FIG. 10, when the absolute value of the defocus amount is less than the predetermined threshold value Dt1, it is in the vicinity of in-focus, and when the absolute value of the defocus amount is equal to or greater than the predetermined threshold value Dt1, it is out of focus. (Focus). However, when the absolute value of the image shift amount is less than the predetermined threshold, it is determined that the focus is near, and when the absolute value of the image shift amount is equal to or greater than the predetermined threshold, it is determined that it is out of focus (large defocus). May be.

  In the operation flow of FIG. 10, when the absolute value of the defocus amount is less than the predetermined threshold, the focus is near, and when the absolute value of the defocus amount is equal to or greater than the predetermined threshold, it is out of focus (large defocus). It is determined. In this way, the final calculated defocus amount value changes discontinuously depending on whether or not the absolute value of the defocus amount is equal to or greater than a predetermined threshold value.

  FIG. 11 is a diagram showing the relationship between the actual defocus amount and the calculated defocus amount, with the actual defocus amount on the horizontal axis and the calculated defocus amount on the vertical axis. When no error is included in the calculated defocus amount, the relationship between the actual defocus amount and the calculated defocus amount is a linear relationship that passes through the origin and has an inclination of 45 degrees, as indicated by a one-dot chain line 301. However, as will be described later, however, as the absolute value of the actual defocus amount increases, the absolute value of the calculated defocus amount tends to be larger than the absolute value of the actual defocus amount due to an error. A broken line 302 is a graph showing the relationship between the actual defocus amount and the calculated defocus amount including an error. When changing the conversion coefficient between near focus and out of focus (large defocus) according to the operation flow of FIG. 10 (when converting the conversion coefficient outside the focus vicinity to smaller than the conversion coefficient near the focus) The relationship between the actual defocus amount and the calculated defocus amount is a graph indicated by solid lines 303a and 303b. According to the graphs indicated by the solid lines 503a and 503b, the error at the time of large defocus is reduced, but the value changes discontinuously at the transition between the vicinity of the focus and the vicinity of the focus out (large defocus). In FIG. 11, the range within ± def of the actual defocus value corresponds to the vicinity of in-focus, and the other range corresponds to the out-of-focus vicinity (large defocus).

  Therefore, for example, as shown in FIG. 12, the conversion coefficient Kd is determined by calculation so that the conversion coefficient Kd changes continuously according to the absolute value of the image shift amount. Or it is good also as determining statistically based on experiment evaluation according to the lens information of the interchangeable lens 202, and the information regarding a to-be-photographed object. According to FIG. 12, the value of the conversion coefficient Kd when the absolute value of the image shift amount is 0 is k0, and the value of the conversion coefficient Kd is smoothly smaller than k0 as the absolute value of the image shift amount increases. The value k1 of the conversion coefficient Kd when the absolute value s1 (> 0) of the image shift amount is smaller than k0. The value of the conversion coefficient Kd is determined based on the detected absolute value of the image shift amount based on FIG. 12, and the image shift amount is converted into a defocus amount using the determined value of the conversion coefficient Kd. In this way, the discontinuous change in the finally calculated defocus amount can be eliminated and the error can be reduced, and the relationship between the actual defocus amount and the calculated defocus amount is shown by the one-dot chain line 301 in FIG. It becomes possible to approximate to.

  When the conversion coefficient is not adjusted according to whether the focus is close or not, as the absolute value of the actual defocus amount increases as indicated by a broken line 302 in FIG. 11, the absolute value of the calculated defocus amount becomes the actual defocus amount. The qualitative reason why it becomes larger than the absolute value will be described.

  Such a phenomenon is caused by the distribution of the light quantity along the direction in which the pair of distance measurement pupils are aligned in each of the pair of distance measurement pupil distributions (that is, the light quantity distribution of the pair of focus detection light beams on the distance measurement pupil plane). This is due to the fact that the center of gravity of the light quantity distribution is not symmetric. In the following description, the expression “asymmetry of the blurred image” also indicates that the light amount distribution along the alignment direction of the pair of blurred images is asymmetric with respect to the center of gravity of the light amount distribution.

  FIG. 13 shows focus detection pixels (focus points arranged on the image sensor 212 corresponding to the focus detection area 101 in FIG. 2) arranged in the center of the imaging plane 96 from a pair of distance measurement pupils on the distance measurement pupil plane 90. It is a figure which shows the relationship of a pair of focus detection light beam which arrives at a detection pixel. FIG. 13 is a diagram showing the relative positions of the planned focal plane 97 of the optical system near the in-focus state and the planned focal plane 98 of the optical system outside the near-focus position with respect to the imaging plane 96. A pair of distance measurement pupil distributions 402 and 403 which are light quantity distributions of the pair of focus detection light beams on the distance measurement pupil plane 90 are the shapes of the light receiving regions of the photoelectric conversion units 12a, 13a, 12b and 13b as shown in FIG. Is equivalent to a pair of projection images corresponding to the distance measuring pupils 92 and 93 when projected onto the distance measuring pupil plane 90 by the microlenses 10a, 10b, 10c and 10d. The outer peripheries of the pair of projection images are limited to a substantially circular shape by an aperture opening or the like, and blurring occurs in the shape of the pair of projection images due to diffraction and aberration by the microlens. Accordingly, the pair of focus detection light beams on the distance measurement pupil plane 90 forms a pair of distance measurement pupil distributions that are bell-shaped and have a skirt extending on one side. When the pair of distance measuring pupil distributions are scanned with a slit perpendicular to the direction in which the pair of distance measuring pupils 92 and 93 are arranged, a pair of distance measuring pupil distributions 402 and 403 as shown in FIG. 13 are obtained.

  Since the outer periphery of the distance measurement pupil distributions 402 and 403 is limited by the aperture of the optical system, it decreases relatively rapidly toward the outer periphery, but the base of the overlapping portion of the distance measurement pupil distributions 402 and 403 is limited by the aperture. Since it is not performed, the distribution decreases relatively slowly, and the distribution shape is extended. In FIG. 13, with respect to barycentric lines 412 and 413 passing through the barycentric positions of the distance measuring pupil distributions 402 and 403, the distance measuring pupil distribution on the side to which the overlapping part of the distance measuring pupil distributions 402 and 403 belongs, and the overlapping part The distance measurement pupil distribution on the side that does not belong is asymmetric, that is, the distance measurement pupil distributions 402 and 403 are asymmetric.

  It is assumed that a point image (or a line image perpendicular to the paper surface) is formed at the center P0 on the imaging surface 96 by the optical system. When the defocus amount between the planned focal plane 98 and the imaging plane 96 is relatively large (out of focus), the pair of focus detection light beams on the planned focal plane 98 forms a pair of blurred images 502 and 503. Form. FIG. 14 shows the light amount distribution shapes of the blurred images 502 and 503 at the time of large defocusing. The light amount distribution shapes of the blurred images 502 and 503 are substantially similar to the light amount distribution shapes of the distance measurement pupil distributions 402 and 403. It has become. Accordingly, the light amount distribution shape of each of the pair of blurred images is also asymmetric. That is, in each of the pair of blurred images, the light amount distribution along the arrangement direction of the pair of blurred images is asymmetric with respect to the center of gravity of the light amount distribution. The centroid lines 512 and 513 passing through the centroid positions of the blurred images 502 and 503 in FIG. 14 indicate the centroid positions of the distance measurement pupil distributions 402 and 403 and the point image at the center P0 on the imaging plane 96 in FIG. Are substantially coincident with the positions where the straight lines 322 and 323 connecting the two and the planned focal plane 98 intersect.

  Conventionally, as a conversion coefficient for converting the image shift amount into the defocus amount, a value obtained by dividing the distance measurement pupil distance by the distance between the centroids of the pair of distance measurement pupil distributions is used. That is, in FIG. 13, the distance between the straight lines 322 and 323 is the image shift amount, and a proportionality coefficient in the proportional relationship between the image shift amount and the defocus amount (for converting the image shift amount into the defocus amount). Conversion coefficient) is based on the premise that it is equal to the proportional coefficient in the proportional relationship between the distance between the center of gravity of each pair of distance measurement pupil distributions and the distance measurement pupil distance, and the proportional coefficient is used as a conversion coefficient from the image shift amount. Conversion to defocus amount is performed. FIG. 15 is a conceptual diagram in the case where the blur images 502 and 503 shown in FIG. 14 are relatively shifted and the centroid lines 512 and 513 passing through the respective centroid positions are matched based on such a premise. On the other hand, FIG. 16 shows a blurred image in which the correlation degree is maximized using the differential phase difference detection calculation (equations (1) and (6)), that is, the correlation amount C (k) is minimized. It is a conceptual diagram at the time of shifting 502 and 503 relatively.

  The relative shift amount (image shift amount) of the blurred images 502 and 503 in FIG. 16 is larger than the relative shift amount (image shift amount) of the blur images 502 and 503 in FIG. This is because the light amount distribution shapes of the blurred images 502 and 503 are substantially similar to the light amount distribution shapes of the distance measurement pupil distributions 402 and 403 and are asymmetric to each other. As shown in FIG. 14, the light amount distribution shape of the blurred image 502 has a skirt extending toward the blurred image 503 side, and the light amount distribution shape of the blurred image 503 has a skirt extending toward the blurred image 502 side. That is, it approaches the other blurred image side. In the differential phase difference detection calculation, an image shift amount that conceptually minimizes the area of the mismatched portion between the blurred images 502 and 503 shown in FIG. 16 is calculated. The contribution of the portion with a large amount of light in the image distribution (that is, the portion near the outer peripheral direction of the blurred image) is large. Therefore, the image displacement amount calculated by the differential phase difference detection calculation is larger than the image displacement amount when the relative shift is performed so that the center of gravity positions of the pair of blurred images coincide with each other. .

  Accordingly, in large defocus, the image shift amount calculated by the differential phase difference detection calculation is determined based on the distance between the center positions of the pair of distance measurement pupil distributions (distance between the pupil distribution center positions). The defocus amount calculated by multiplying the conversion coefficient is larger than the original defocus amount.

  When the defocus amount between the planned focal plane 97 and the imaging plane 96 is relatively small (in the vicinity of in-focus), the pair of focus detection light beams form a pair of blurred images 602 and 603 on the planned focal plane 97. To do. FIG. 17 shows the light amount distribution shapes of the blurred images 602 and 603. The light amount distribution shapes of the blurred images 602 and 603 near the in-focus state are respectively point images at the center P0 on the imaging plane 96. It becomes a substantially similar and symmetrical shape. The centroid position through which the centroid lines 612 and 613 of the blurred images 602 and 603 in FIG. 17 pass is the centroid position of the distance measurement pupil distributions 402 and 403 and the point image at the center P0 on the imaging plane 96 in FIG. The positions of the connected straight lines 322 and 323 and the planned focal plane 97 substantially coincide with each other.

  FIG. 18 is a conceptual diagram in the case where the blurred images 602 and 603 shown in FIG. 17 are relatively shifted so that the centroid lines 612 and 613 passing through the respective centroid positions are matched. Further, the blurred images 602 and 603 are obtained by using the differential phase difference detection calculation (formulas (1) and (6)) so that the degree of correlation becomes the highest, that is, the correlation amount C (k) is minimized. A conceptual diagram in the case of relative shifting is also substantially the same as FIG. That is, the light intensity distribution shapes of the blurred images 602 and 603 in the vicinity of the in-focus are substantially symmetrical with respect to the centroid lines 612 and 613 passing through the respective centroid positions. Therefore, the relative shift amount (image shift amount) when the blur images 602 and 603 are relatively shifted so that the barycentric lines 612 and 613 passing through the barycentric positions of the blur images 602 and 603 coincide with each other, and the blur image. The relative shift amount (image shift amount) when the blurred images 602 and 603 are relatively shifted so that the degree of coincidence (correlation degree) between 602 and 603 is high substantially coincides. Therefore, the image shift amount calculated by the differential phase difference detection calculation is multiplied by a conversion coefficient determined based on the distance between the center positions of the pair of distance measurement pupil distributions (the distance between the pupil distribution center positions). The error between the calculated defocus amount and the original defocus amount is reduced.

  FIG. 13 shows a case where the imaging plane is on the same side as the optical system with respect to the planned focal plane. Even in the case where the imaging plane is on the opposite side of the optical system with respect to the planned focal plane, for the same reason as described above, near the in-focus position, the pupil shifts to the image shift amount calculated by the differential phase difference detection calculation. The error between the defocus amount calculated by multiplying the conversion coefficient determined based on the distance between the distribution centroid positions and the original defocus amount becomes small. In large defocusing, the defocus amount calculated by multiplying the image shift amount calculated by the differential phase difference detection calculation by the conversion coefficient determined based on the distance between the pupil distribution centroid positions is the original defocus amount. The value is larger than the defocus amount.

  In the above description, the image formed on the imaging surface 96 by the optical system is described as a point image. However, if a general image that is not a point image is regarded as a set of point images, the optical system Even when a general image is formed on the imaging surface 96, it can be explained in the same manner as described above.

  The shape of the distance measurement pupil distributions 402 and 403 shown in FIG. 13 corresponds to the case where the F value of the optical system is relatively small, but the distance measurement pupil distribution when the F value of the optical system is relatively large is shown in FIG. The distance measurement pupil distributions 404 and 405 shown in FIG. In FIG. 19, the shape of each of the distance measurement pupil distributions 404 and 405 is asymmetric with respect to the center of gravity lines 414 and 415 passing through the position of the center of gravity of the distance measurement pupil distributions 404 and 405. The degree of asymmetry of the shape is improved compared to the distance measurement pupil distributions 402 and 403 shown in FIG. Therefore, at the time of large defocus, the defocus amount calculated by multiplying the image shift amount calculated by the differential phase difference detection calculation by the conversion coefficient determined based on the distance between the pupil distribution centroid positions, The difference from the defocus amount (the error included in the calculated defocus amount) is small when the F value of the optical system is relatively large. That is, the value of the ratio between the conversion coefficient in the vicinity of focusing and the conversion coefficient in the vicinity of in-focus is larger when the F value of the optical system is relatively larger than when the F value of the optical system is relatively small. Closer to 1. Thus, by determining the conversion coefficient according to the F value of the optical system, more accurate focus detection can be performed.

  The distance between centroid lines 414 and 415 shown in FIG. 19 (distance between pupil distribution centroid positions) is smaller than the distance between centroid lines 412 and 413 (distance between pupil distribution centroid positions) in FIG. . As described above, the conversion coefficient for converting the image shift amount into the defocus amount is the distance between the centroids of the pair of distance measurement pupil distributions (the distance between the pupil distribution centroid positions). The divided value is used. Therefore, the conversion coefficient increases as the distance between the pupil distribution centroid positions decreases. As described above, the shape of the distance measurement pupil distributions 402 and 403 shown in FIG. 13 corresponds to the case where the F value of the optical system is relatively small, and the shape of the distance measurement pupil distributions 404 and 405 shown in FIG. This corresponds to the case where the F value is relatively large. Therefore, the larger the F value of the optical system, the larger the conversion coefficient.

  For the focus detection pixels arranged in the image sensor 212 corresponding to the focus detection areas 102 and 103 in FIG. 2, the exit pupil distances dn and df of the optical system do not match the distance measurement pupil distance d as shown in FIG. In this case, the pair of focus detection light fluxes are nonuniformly limited by vignetting. In such a case, the shape of the pair of ranging pupil distributions on the ranging pupil plane 90 is different from the ranging pupil distributions 402 and 403 shown in FIG. 13, and the ranging pupil distributions 406 and 407 shown in FIG. It is expressed as In FIG. 20, regarding the barycentric lines 416 and 417 passing through the barycentric positions of the distance measuring pupil distributions 406 and 407, not only the shapes of the distance measuring pupil distributions 406 and 407 are asymmetric but also the distance measuring pupil distributions 406 and 407. The difference in shape between the distance measurement pupil distributions 402 and 403 that are not affected by vignetting is larger than the difference in shape between the distance measurement pupil distributions 402 and 403. Therefore, regarding the value of the ratio between the conversion coefficient in the vicinity of the focus and the conversion coefficient in the vicinity of the focus, the focus detection pixel at the center on the imaging surface corresponding to the focus detection area 101 arranged at the center of the shooting screen 100. The ratio value when focus detection processing is performed based on the photoelectric conversion signal and the photoelectric conversion of the peripheral focus detection pixels on the imaging surface corresponding to the focus detection areas 102 and 103 arranged around the photographing screen 100 The ratio value when the focus detection process is performed based on the signal needs to be different. Specifically, since the value of the ratio depends on the above-described vignetting state, a value obtained in advance by experiment according to the type of the interchangeable lens 202 may be used. A value that is statistically determined based on the image height may be used. The ratio value corresponding to the focus detection pixel at a high image height, such as the focus detection pixels arranged in the image sensor 212 corresponding to the focus detection areas 102 and 103, is calculated based on FIG. As described above, by adjusting the conversion coefficient in the vicinity of the focus and the conversion coefficient in the vicinity of the focus according to the position where the focus detection pixel is arranged, that is, the image height, more accurate focus detection can be performed. .

  There are the following methods (1) to (3) for determining the value of the conversion coefficient in the vicinity of in-focus and the value of the conversion coefficient in the vicinity of in-focus (large defocus). For example, a conversion coefficient determination device (not shown) having a computer is included in the body drive control device 214, and the values of the conversion coefficients are obtained by the methods (1) to (3) according to an arithmetic program stored in the conversion coefficient determination device. Based on the determined value of the conversion coefficient, a conversion coefficient lookup table described below is created and stored in the body drive control device 214.

(1) Method of Finding Conversion Coefficients by Theoretical Calculation The conversion coefficient determination apparatus is configured by the shape of the distance measurement pupil distributions 402 and 403 in FIG. 13, the shape of the distance measurement pupil distributions 404 and 405 in FIG. 19, and the distance measurement in FIG. The shape of the pupil distributions 406 and 407, the optical characteristics of the exit pupil of the optical system, the optical design parameters of the focus detection pixel (microlens diameter, distance from the microlens to the photoelectric conversion unit, etc.), distance measurement pupil distance, focus detection pixel Is specified in advance based on the image height or the like. The optical characteristics of the exit pupil of the optical system include the exit pupil distance of the optical system, the exit pupil diameter of the optical system, and the F value of the optical system. The conversion coefficient determination device includes a pair of distance measurement pupil distributions 402 and 403 shown in FIG. 13 whose shape has been specified, a pair of distance measurement pupil distributions 404 and 405 shown in FIG. 19, and a pair of distance measurement pupil distributions 406 shown in FIG. , 407 is calculated and obtained by dividing the distance between the centroid positions in each pair of distance measurement pupil distributions by the distance measurement pupil distance, thereby calculating a conversion coefficient in the vicinity of the in-focus state. Based on the calculated conversion coefficient in the vicinity of the in-focus state, the conversion coefficient determination device is configured to provide optical characteristics of the exit pupil of the optical system (exit pupil distance, exit pupil diameter and F value of the optical system), ranging pupil distance, and focus detection pixel. Create a conversion coefficient lookup table using the image height of the input as an input parameter.

  Further, the conversion coefficient determination apparatus estimates and calculates the distribution shape of the blurred image at a predetermined defocus amount at the time of large defocus as shown in FIG. 14 based on the distance measurement pupil distribution obtained by calculation, and calculates the calculated blur image. A differential phase difference detection correlation calculation is performed on the distribution, and a conversion coefficient outside the vicinity of the focus is calculated based on the image shift amount obtained based on the calculation result and the above-described predetermined defocus amount. The conversion coefficient determination device calculates the optical characteristics of the exit pupil of the optical system (exit pupil distance, exit pupil diameter and F value) of the optical system, the image height of the focus detection pixel, and the like based on the calculated conversion coefficient outside the vicinity of the focus. Create a lookup table of conversion coefficients as input parameters. The conversion coefficient determination device stores the created lookup table in the body drive control device 214.

  If the distance measurement pupil distribution or blur image distribution is calculated, the error may increase. Therefore, the distance measurement pupil distribution and blur image distribution are actually measured, and the measured distance pupil distribution and blur image distribution are measured. It is also possible to calculate the above-described conversion coefficient using, and create a conversion coefficient lookup table.

  When converting the image shift amount to the defocus amount at the time of actual focus detection processing, the body drive control device 214 relates to the optical characteristics of the exit pupil of the optical system from the interchangeable lens 202 mounted on the camera body 203. Information, ie, exit pupil distance, exit pupil diameter, and F value information is read. The body drive control device 214 refers to the look-up table based on the read information and the image height of the focus detection pixel corresponding to the focus detection area where focus detection is performed, and the conversion coefficient Kd1 in the vicinity of the focus and A conversion coefficient Kd2 outside the focus vicinity (large defocus) is acquired. The body drive control device 214 calculates the defocus amount by multiplying the acquired conversion coefficient by the image shift amount shft calculated by the differential phase difference detection correlation calculation.

  When the calculation calculation of the conversion coefficient can be performed in a short time during the actual focus detection process, it is not necessary to create the conversion coefficient lookup table described above. In that case, the body drive control device 214 having a conversion coefficient determination device therein includes information on the optical characteristics of the exit pupil of the optical system read from the interchangeable lens 202 attached to the camera body 203 (exit pupil distance, exit pupil diameter). And F value information), the image height of the focus detection pixel corresponding to the focus detection area where the focus detection is performed, the optical parameters of the focus detection pixel, and the like. It is also possible to calculate and convert the image shift amount to the defocus amount based on the calculated conversion coefficient.

(2) Method of measuring the conversion coefficient for each interchangeable lens The distance pupil distribution and blur image distribution are affected by the aberration of the optical system, so each optical system actually used during the focus detection process The conversion coefficient near the focus and the conversion coefficient outside the focus may be measured in advance by the conversion coefficient determination device. A look-up table of the measured conversion coefficient is created by the conversion coefficient determination device using the F value and focal length of the optical system and the image height as parameters, and is stored in advance in the lens drive control device 206 on the interchangeable lens 202 side. . When performing conversion from the image shift amount to the defocus amount during the actual focus detection process, the body drive control device 214 sends the image height to the interchangeable lens 202 attached to the camera body 203. The lens drive control device 206 of the interchangeable lens 202 receives a conversion coefficient near the in-focus state and an out-of-focus area (large data) according to the F value set when the image height is received, the focal length, and the received image height. The conversion coefficient in (focus) is sent to the body drive control device 214 on the camera body side. The body drive control unit 214 of the camera body converts the image shift amount into the defocus amount using the received conversion coefficient in the vicinity of in-focus and the conversion coefficient in the vicinity of in-focus (large defocus). That is, the body drive control device 214 uses the conversion coefficient measured in advance corresponding to the same optical system as the optical system of the actual interchangeable lens 202 mounted on the camera body 203 to descale the image shift amount. Convert to focus amount.

  In the above-described measurement of the conversion coefficient in the vicinity of the in-focus state, a point image or a line image is formed on the imaging plane by each interchangeable lens 202, and the imaging plane is minute in the optical axis direction of the interchangeable lens 202 with respect to the planned focal plane. The relationship between the displacement amount and the image shift amount calculated by the differential phase difference detection correlation calculation is measured. A value obtained by dividing the measured displacement amount by the calculated image shift amount is determined as the value of the conversion coefficient. When the relationship between multiple sets of displacement and image displacement is measured, it is possible to obtain higher accuracy by determining the conversion coefficient value near the focus based on the slope of the regression line when the relationship is graphed. It is also possible to perform measurement of various conversion coefficients.

  In the measurement of the conversion coefficient outside the vicinity of the in-focus position, the image forming surface on which a point image or a line image is formed by each interchangeable lens 202 is displaced by a large defocus amount in the optical axis direction of the interchangeable lens 202 with respect to the intended focal plane. A displacement amount that is sometimes measured, and an image shift amount calculated by performing a differential phase difference detection correlation operation on a blurred image formed on the planned focal plane corresponding to the point image or the line image The relationship is measured. A value obtained by dividing the measured displacement amount by the calculated image shift amount is determined as the value of the conversion coefficient.

(3) Method of using a value measured with respect to the reference optical system as a conversion coefficient It takes time and effort to measure the conversion coefficient for each optical system as in the method (2) described above. According to the method (3), the conversion coefficient determination device measures the conversion coefficient in the vicinity of focusing and the conversion coefficient in the vicinity of focusing using the F value, exit pupil distance, and image height as parameters in a predetermined reference optical system. Then, a lookup table of the measured conversion coefficients is created, and the lookup table is stored in advance in the body drive control device 214 on the camera body 203 side. When converting from the image shift amount to the defocus amount at the time of actual focus detection, the body drive control device 214 includes information on the F value and the exit pupil distance read from the interchangeable lens 202 attached to the camera body 203. Based on the image height of the focus detection pixel corresponding to the focus detection area where focus detection is performed, the conversion coefficient near the focus and the conversion coefficient outside the focus vicinity (large defocus) are obtained by referring to the lookup table. Then, the defocus amount is calculated based on the acquired conversion coefficient. That is, even when the interchangeable lens 202 attached to the camera body 203 has an optical system different from the predetermined reference optical system, the defocus amount is based on the conversion coefficient measured in the predetermined reference optical system. Calculated.

  The present invention solves that the conversion coefficient outside the focus vicinity (large defocus) calculated by the methods (1), (2), and (3) described above prevents an increase in conversion error outside the focus vicinity. However, the accuracy as high as the conversion coefficient in the vicinity of the focus is not required. For example, the conversion coefficient in the vicinity of the focus may be simply obtained by multiplying the conversion coefficient in the vicinity of the focus by an adjustment coefficient (<1) corresponding to the image shift amount. By setting the adjustment coefficient to a value less than 1, for example, 0.8, the conversion coefficient outside the focus vicinity can be obtained, thereby solving the above-described problem of preventing an increase in conversion error outside the focus vicinity. The conversion coefficient determining device multiplies the adjustment coefficient in the vicinity of the focus by the adjustment coefficient based on the adjustment coefficient stored in advance in the conversion coefficient determination device and the calculation program, and calculates the conversion coefficient outside the focus vicinity. To do.

In the above-described embodiment, the correlation amount C (k) is calculated for the pair of data strings by the differential correlation calculation process including the subtraction using the correlation calculation formula (1) or (6). For example, the correlation amount C (k) may be calculated by multiplication type correlation calculation processing including multiplication using the following correlation calculation formula (10). In the correlation calculation according to Expression (10), the correlation amount C (k) indicates a characteristic that takes a maximum value in the phase difference k when the correlation degree of the pair of data strings corresponding to the degree of coincidence of the pair of images is the highest. . The larger the correlation amount C (k) is, the higher the degree of correlation is.
C (k) = Σ (A1 _n × A2 _{n + k} ) (10)

  In the imaging device 212 illustrated in FIG. 3, the focus detection pixels 312 and 313 include one photoelectric conversion unit in one pixel. However, a pair of photoelectric conversion units may be included in one pixel. . FIG. 21 shows an image sensor 212B of a modification corresponding to the image sensor 212 shown in FIG. In FIG. 21, the focus detection pixel 311 includes a pair of photoelectric conversion units in one pixel. The focus detection pixel 311 illustrated in FIG. 21 performs a function corresponding to the pair of the focus detection pixel 312 and the focus detection pixel 313 illustrated in FIG.

  The focus detection pixel 311 includes a microlens 10 and a pair of photoelectric conversion units 22 and 23. The focus detection pixel 311 is not provided with a color filter in order to increase the amount of light. The spectral sensitivity characteristic indicated by the focus detection pixel 311 is a spectral sensitivity characteristic that combines the spectral sensitivity characteristic of a photodiode that performs photoelectric conversion included in the photoelectric conversion unit and the spectral sensitivity characteristic of an infrared cut filter (not shown). That is, the focus detection pixel 311 exhibits spectral sensitivity characteristics that are obtained by adding the spectral sensitivity characteristics of green pixels, red pixels, and blue pixels. The light wavelength region exhibiting high sensitivity includes the light wavelength region in which each color filter exhibits high sensitivity in each of the green pixel, red pixel, and blue pixel.

  In the above-described embodiment, the focus detection operation by the pupil division method using the microlens has been described. However, the present invention is not limited to the focus detection of such a method, and is disclosed in JP-A-7-159680. The focus detection by the re-imaging pupil division method as described above can also be applied when the distribution of the pair of distance measurement pupils is asymmetric with respect to the respective distribution center positions.

  In the imaging device 212 illustrated in FIG. 3, an example in which the imaging pixel 310 includes a Bayer color filter is shown, but the configuration and arrangement of the color filter are not limited thereto. For example, an array of complementary color filters (green: G, yellow: Ye, magenta: Mg, cyan: Cy) may be employed.

  In the image sensor 212 shown in FIG. 3, the focus detection pixels 312 and 313 are not provided with a color filter. However, one of the color filters (for example, a green filter) of the image pickup pixel 310 is used as the focus detection pixel. Even when 312 and 313 are provided, the present invention can be applied.

  In the imaging device 212 shown in FIG. 3, the example in which the imaging pixels 310 and the focus detection pixels 312 and 313 are arranged in a dense square lattice arrangement is shown, but they may be arranged in a dense hexagonal lattice arrangement.

  The imaging device is not limited to a digital still camera or a film still camera having a configuration in which an interchangeable lens is attached to the camera body as described above. For example, the present invention can also be applied to a lens-integrated digital still camera, film still camera, or video camera. Furthermore, the present invention can be applied to a small camera module built in a mobile phone, a surveillance camera, a visual recognition device for a robot, and the like. The present invention can also be applied to a focus detection device other than a camera, a distance measuring device, and a stereo distance measuring device.

10 microlens, 11, 12, 13, 22, 23 photoelectric conversion unit,
72, 73, 82, 83 Focus detection luminous flux,
90 Distance pupil plane, 91 Optical axis, 92, 93 Distance pupil, 95 Exit pupil,
96 Imaging plane, 97, 98 Planned focal plane,
100 shooting screen, 101, 102, 103 focus detection area,
172, 173, 182, 183 Focus detection light flux,
201 digital still camera, 202 interchangeable lens, 203 camera body,
204 mount unit, 206 lens drive control device,
208 zooming lens, 209 lens, 210 focusing lens,
211 Aperture, 212 Image sensor, 213 Electrical contact,
214 body drive control device,
215 liquid crystal display element driving circuit, 216 liquid crystal display element, 217 eyepiece,
219 memory card,
272, 273, 282, 283, 292, 293, focus detection light flux,
301 dashed line, 302 broken line, 303 solid line,
310 imaging pixels, 311, 312, 313 focus detection pixels,
322, 323 straight line,
402, 403, 404, 405, 406, 407 Distance pupil distribution,
412, 413, 414, 415, 416, 417 center of gravity line,
502, 503, 602, 603 blurred image,
512, 513, 612, 613

Claims (14)

A plurality of focus detection pixels that receive a pair of light beams passing through an exit pupil plane of the optical system and output a pair of signals;
An image shift amount detecting means for detecting an image shift amount of the pair of images by the pair of light fluxes by the correlation calculation processing for the pair of signals;
Defocus amount calculation means for calculating a defocus amount of the optical system by multiplying the image shift amount by a predetermined conversion coefficient;
Each of the light quantity distributions of the pair of light fluxes on the exit pupil plane has an asymmetry with respect to the distribution centroid of each of the pair of light quantity distributions,
The defocus amount calculating means uses the first value as the value of the predetermined conversion coefficient in the in-focus state where the calculated absolute value of the defocus amount is less than a predetermined threshold, and the absolute value is A focus detection apparatus using a second value smaller than the first value as the value of the predetermined conversion coefficient in a large defocus state that is equal to or greater than the predetermined threshold. The focus detection apparatus according to claim 1,
The first value is determined to increase as the F value of the optical system increases,
The focus detection apparatus according to claim 1, wherein the ratio value between the first value and the second value approaches 1 as the F value of the optical system increases. The focus detection apparatus according to claim 1,
In the in-focus state, the first value is the amount of displacement of the imaging plane measured when the imaging plane of the optical system is displaced in the optical axis direction of the optical system, and the image displacement. A focus detection apparatus characterized in that the focus detection apparatus is determined based on a relationship with the image shift amount detected by an amount detection means. The focus detection apparatus according to claim 3,
The focus detection apparatus, wherein the optical system when the relationship is measured is a predetermined reference optical system. The focus detection apparatus according to claim 3,
The focus detection apparatus characterized in that the optical system when the relationship is measured is the same as the optical system when the defocus amount is calculated by the defocus amount calculation means. The focus detection apparatus according to claim 1,
The focus detection apparatus, wherein the first value is determined based on an F value of the optical system, an exit pupil distance of the optical system, and an exit pupil diameter of the optical system. The focus detection apparatus according to claim 1,
In the large defocus state, the second value is determined by the amount of displacement of the imaging plane measured when the imaging plane of the optical system is displaced in the optical axis direction of the optical system, and the image displacement. A focus detection apparatus characterized in that the focus detection apparatus is determined based on a relationship with the image shift amount detected by an amount detection means. In the focus detection apparatus according to any one of claims 1 to 6,
The focus detection apparatus according to claim 1, wherein the second value is obtained by multiplying the first value by an adjustment coefficient less than 1. The focus detection apparatus according to claim 1,
A ratio value of the first value and the second value of the predetermined conversion coefficient multiplied by the image shift amount detected at the center on the image plane of the optical system; The focus detection apparatus, wherein the ratio value between the first value and the second value of the predetermined conversion coefficient multiplied by the image shift amount detected in the vicinity is different. The focus detection apparatus according to claim 1,
The correlation calculation process is a differential correlation calculation process including subtraction for the pair of signals,
The image shift amount detection means relatively displaces the pair of signals, and the difference type correlation calculation processing for the pair of relatively displaced signals causes a difference between the pair of relatively displaced signals. Detecting the amount of correlation, and detecting the amount of image shift based on the phase difference when the amount of correlation changing according to the phase difference between the pair of relatively displaced signals exhibits a minimum value. A focus detection device. The focus detection apparatus according to claim 10, wherein
The pair of signals includes one signal A1 _{1 to} A1 _n including n signals and the other signal A2 _{1 to} A2 _n including _n signals,
The correlation amount C (k) that changes according to the phase difference k between the pair of relatively displaced signals is expressed by the equation “C (k) = Σ | A1 _n · A2 _{n + 1 + k−} A2”. _{n + k} · A1 _{n + 1} || ”. The focus detection apparatus according to claim 1,
The plurality of focus detection pixels include a first focus detection pixel and a second focus detection pixel,
The first focus detection pixel includes a microlens and a first photoelectric conversion unit corresponding to the microlens, and receives one of the pair of light beams.
The second focus detection pixel includes a microlens and a second photoelectric conversion unit corresponding to the microlens, and receives the other of the pair of light beams. The focus detection device according to any one of claims 1 to 12,
A focus adjustment device comprising: a focus adjustment unit that performs focus adjustment of the optical system according to the defocus amount calculated by the focus detection device. A plurality of focus detection pixels that receive a pair of light beams passing through an exit pupil plane of the optical system and output a pair of signals;
An image shift amount detecting means for detecting an image shift amount of the pair of images by the pair of light fluxes by the correlation calculation processing for the pair of signals;
Defocus amount calculation means for calculating a defocus amount of the optical system by multiplying the image shift amount by a predetermined conversion coefficient;
The defocus amount calculating means uses the first value as the value of the predetermined conversion coefficient in the in-focus state where the calculated absolute value of the defocus amount is less than a predetermined threshold, and the absolute value is A focus detection apparatus using a second value smaller than the first value as the value of the predetermined conversion coefficient in a large defocus state that is equal to or greater than the predetermined threshold.

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