JP4992481B2 - Focus detection apparatus and imaging apparatus - Google Patents

Description

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

A pair of luminous fluxes arriving from the imaging optical system by arranging the focus detection pixels of the pupil division type phase difference detection method, which is composed of a microlens and a pair of photoelectric conversion units arranged behind the microlens, on the imaging surface of the imaging optical system There is known a focus detection device that calculates an image shift amount of a pair of images formed by the above based on an output of a focus detection pixel and detects a focus adjustment state of an imaging optical system (for example, see Patent Document 1). ).
In this type of focus detection device, a pair of light fluxes passing through a pair of areas on a plane (a distance measurement pupil plane) that is a predetermined distance away from the plane on which focus detection pixels are arranged in the direction of the exit pupil of the imaging optical system. The image shift amount of the pair of images formed on the focus detection pixel array surface is detected by the focus detection pixel array. Further, even when an unbalance occurs in the pair of light beams for focus detection, the focus detection pixel output is filtered to prevent a decrease in focus detection accuracy.

Prior art documents related to the invention of this application include the following.
JP 2004-138968 A

  However, the conventional pupil division type phase difference detection type focus detection apparatus described above is used in combination with various imaging optical systems, but the exit pupil distance of the imaging optical system is far from the above-mentioned distance measurement pupil distance. In this case, the degree of unbalance between the pair of light beams increases around the imaging screen of the imaging optical system, and the unbalance between the pair of images also increases, so that the focus detection is performed by filtering the output of the focus detection pixels. There is a limit to preventing the loss of accuracy. Furthermore, when the degree of unbalance between the pair of light beams for focus detection increases, only one of the pair of light beams enters the exit pupil of the imaging optical system, and one of the pair of images disappears. As a result, focus detection becomes impossible.

According to a first aspect of the present invention, there is provided a focus detection apparatus which is disposed on a predetermined focal plane of the imaging optical system in an imaging apparatus which can be mounted by replacing a plurality of types of imaging optical systems having different exit pupil distances. A first focus detection pixel and a second focus that receive a pair of light beams passing through the image optical system and output a pair of image signals used for phase difference detection for detecting a focus detection adjustment state of the imaging optical system. A focus detection calculation that detects a focus adjustment state of the imaging optical system based on a focus detection element in which a plurality of detection pixels are arranged, and output signals of the plurality of first focus detection pixels and the plurality of second focus detection pixels. And the first focus detection pixel includes a first microlens and a first photoelectric conversion unit that receives light via the first microlens, and the first photoelectric conversion unit A predetermined distance from the focal plane (ranging pupil distance In a pupil plane (referred to as a distance measurement pupil plane) set to the first focus detection pixel, a light beam passing through a first region set in common to all the first focus detection pixels is received, and the second focus detection The pixel includes a second microlens different from the first microlens and a second photoelectric conversion unit that receives light via the second microlens, and the second photoelectric conversion unit is all on the distance measuring pupil plane. Receiving a light beam passing through a second region different from the first region set in common to the second focus detection pixels, and the distance measuring pupil distance is an exit pupil distance of the plurality of types of imaging optical systems An average distance, and the first region and the second region include a third region including the optical axis of the imaging optical system as a common region, and a centroid of the first region and a centroid of the second region The width of the third region in the direction connecting the two is the plurality of types of imaging optics The light flux having the largest F value among the open F values is set shorter than the diameter of the region passing through the distance measuring pupil plane, and the first focus detection pixel and the second focus detection pixel are Arranged alternately along a straight line connecting the centroid of the first area and the centroid of the second area , the plurality of first focus pixels output a first signal data string, and the plurality of second areas The focus pixel outputs a second signal data string, and the focus detection calculation means outputs the first data in the first signal data string and the first signal data string in the second signal data string. The first calculation data is calculated by multiplying the data in the vicinity of the second data corresponding to the data, and the second data in the second signal data string and the first signal data string, The second operation data is obtained by multiplying the data in the vicinity of the first data corresponding to the second data. The degree of correlation between the first calculation data and the second calculation data is calculated, and the defocus amount is calculated based on the correlation amount .
Imaging device according to the invention of claim 4 includes a focus detecting apparatus according to claim 1, a focusing means for performing focus adjustment of the imaging optical system based on the defocus amount calculated by the focus detection computing unit And an image pickup device for picking up an image formed by the imaging optical system.

  According to the present invention, when an image shift amount of a pair of images formed by a pair of light beams coming from the image forming optical system is obtained by correlation calculation, and the focus detection of the image forming optical system is performed, Even if the degree of unbalance between a pair of light beams around the photographing screen is large, the probability that the focus can be detected by the correlation calculation can be increased.

  As an imaging apparatus including the focus detection apparatus according to an embodiment, a lens interchangeable digital still camera will be described as an example. FIG. 1 is a cross-sectional view showing a configuration of a camera according to an embodiment. A digital still camera 201 according to an 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.

  The interchangeable lens 202 includes a lens 209, a zooming lens 208, a focusing lens 210, an aperture 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. The lens drive control device 206 controls the driving of the focusing lens 210 and the aperture 211, detects the state of the zooming lens 208, the focusing lens 210, and the aperture 211, and the like. In addition, the lens information is transmitted and the camera information is received by communication with a body drive control device 214 described later.

  The camera body 203 includes an imaging element 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.

  The body drive control device 214 includes a microcomputer, a memory, a drive control circuit, and the like, and performs drive control of the image sensor 212 and reading of image signals and focus detection signals, image signal processing and recording, and focus detection calculation based on the focus detection signals. The focus adjustment of the interchangeable lens 202 and the operation control of the camera are performed. 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 (defocus amount, aperture value, etc.).

  The liquid crystal display element 216 functions as a liquid crystal viewfinder (EVF: electrical viewfinder). The liquid crystal display element driving circuit 215 displays a through image by the imaging element 212 on the liquid crystal display element 216, and the photographer can observe the through image through the eyepiece lens 217. The memory card 219 is an image storage that stores an image captured by the image sensor 212.

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

  The body drive control device 214 calculates the defocus amount based on the focus detection signal from the focus detection pixel of the image sensor 212 and sends the defocus amount to the lens drive control device 206. In addition, the body drive control device 214 processes the image signal from the image sensor 212 and stores it in the memory card 219, and sends the through image signal from the image sensor 212 to the liquid crystal display element drive circuit 215, and transmits the through image to the liquid crystal. The image is displayed on the 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 control device 206 changes 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 a lookup prepared in advance. Lens information corresponding to the lens position and aperture value is selected from the 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 a focal point according to the lens drive amount. Further, the lens drive control device 206 drives the diaphragm 211 in accordance with the received diaphragm value.

  An interchangeable lens 202 having various imaging optical systems can be attached to the camera body 203 via a mount unit 204, and the camera body 203 is based on the output of focus detection pixels incorporated in the image sensor 212. The focus adjustment state 202 is detected.

  FIG. 2 is a diagram showing the arrangement of focus detection pixels on the shooting screen. When focus detection is performed on the basis of an output of a focus detection pixel array, which will be described later, an area for sampling an image on the shooting screen (focus detection area). , Focus detection position). In this embodiment, an example in which the focus detection area 101 is arranged in the horizontal direction including the center 102 on the photographing screen 100 is shown. Focus detection pixels are linearly arranged in the longitudinal direction of the focus detection area 101 indicated by a rectangle. The end point 103 of the focus detection area 101 is located at a distance S in the horizontal direction from the center 102 of the screen, and focus detection pixels are arranged up to this point.

  FIG. 3 is a front view showing a detailed configuration of the image sensor 212, and is an enlarged view of the vicinity of the focus detection area 101 on the image sensor 212 shown in FIG. In FIG. 3, the vertical and horizontal directions (pixel rows and columns) correspond to the vertical and horizontal directions of the shooting screen shown in FIG. The imaging element 212 includes an imaging pixel 310 including green pixels, blue pixels, and red pixels, and focus detection pixels 312 and 313. The focus detection area 312 (see FIG. 2) includes focus detection pixels 312 and 313. They are alternately arranged in the horizontal direction. The focus detection pixels 312 and 313 are linearly arranged in a row where the green pixel and the blue pixel of the imaging pixel 310 are to be arranged.

  In this embodiment, an element in which focus detection pixels are arranged in a part of a two-dimensional array of imaging pixels will be described as an example, and this element will be referred to as an imaging element for convenience. Since this element is an element constituting the focus detection device, it can also be called a “focus detection element”.

  As shown in FIG. 4, the imaging pixel 310 includes the microlens 10, the photoelectric conversion unit 11, and a color filter (not shown). There are three types of color filters, red (R), green (G), and blue (B), and the respective spectral sensitivities have the characteristics shown in FIG. An imaging pixel having each color filter is arranged in a Bayer array.

  As shown in FIG. 5A, the focus detection pixel 312 includes the microlens 10 and the photoelectric conversion unit 12, and the photoelectric conversion unit 12 is rectangular. As shown in FIG. 5B, the focus detection pixel 313 includes the microlens 10 and the photoelectric conversion unit 13, and the photoelectric conversion unit 13 is rectangular. The photoelectric conversion units 12 and 13 are arranged in the horizontal direction when the microlenses 10 are displayed in a superimposed manner, and the left part of the photoelectric conversion unit 12 and the right part of the photoelectric conversion unit 13 overlap each other. Yes. In the focus detection pixel row on the image sensor 212, the focus detection pixels 312 and the focus detection pixels 313 are alternately arranged in the horizontal direction (alignment direction of the photoelectric conversion units 12 and 13).

  The focus detection pixels 312 and 313 are not provided with a color filter in order to increase the amount of light. The spectral characteristics of the focus detection pixels 312 and 313 are the spectral sensitivity characteristics of a photodiode that performs photoelectric conversion and the spectral sensitivity characteristics of an infrared cut filter (not shown). Is a spectral sensitivity characteristic obtained by adding the spectral sensitivity characteristics of the green pixel, the red pixel, and the blue pixel shown in FIG. 6, and the light wavelength region of the sensitivity is a green pixel. It covers the light wavelength range of red and blue pixel sensitivity.

  The photoelectric conversion unit 11 of the imaging pixel 310 is designed so as to receive all the light beams passing through the exit pupil (for example, F1.0) of the brightest interchangeable lens by the microlens 10. The photoelectric conversion units 12 and 13 of the focus detection pixels 312 and 313 are designed so as to receive all the light beams that pass through a predetermined region (for example, F2.8) of the exit pupil of the interchangeable lens by the microlens 10. .

  FIG. 8 is a cross-sectional view of the imaging pixel 310. In the imaging pixel 310, the microlens 10 (with a diameter of about 8 to 12 μm) is disposed in front of the imaging photoelectric conversion unit 11, and the shape of the photoelectric conversion unit 11 is projected forward by the microlens 10. The photoelectric conversion unit 11 is formed on the semiconductor circuit substrate 29, and a color filter (not shown) is disposed between the microlens 10 and the photoelectric conversion unit 11.

  FIG. 9A is a cross-sectional view of the focus detection pixel 312 arranged at the center of the screen. In the focus detection pixel 312 disposed in the center of the screen, the microlens 10 (about 8 to 12 μm in diameter) is disposed in front of the photoelectric conversion unit 12, and the shape of the photoelectric conversion unit 12 is projected forward by the microlens 10. The The photoelectric conversion unit 12 is formed on the semiconductor circuit substrate 29, and the microlens 10 is integrally and fixedly formed thereon by a semiconductor image sensor manufacturing process.

  FIG. 9B is a cross-sectional view of the focus detection pixel 313 arranged at the center of the screen. In the focus detection pixel 313 disposed in the center of the screen, the micro lens 10 (about 8 to 12 μm in diameter) is disposed in front of the photoelectric conversion unit 13, and the shape of the photoelectric conversion unit 13 is projected forward by the micro lens 10. The The photoelectric conversion unit 13 is formed on the semiconductor circuit substrate 29, and the microlens 10 is integrally and fixedly formed thereon by a semiconductor image sensor manufacturing process.

  The photoelectric conversion unit 12 of the focus detection pixel 312 and the photoelectric conversion unit 13 of the focus detection pixel 313 are arranged at symmetrical positions with respect to the optical axis 300 of the microlens 10 and are cross sections of the focus detection pixels 312 and 313. When the figures are superimposed on the basis of the optical axis 300 of the microlens 10, the photoelectric conversion units 12 and 13 are partially overlapped. Therefore, the light beam 322 that projects the photoelectric conversion unit 12 and the light beam 323 that projects the photoelectric conversion unit 13 partially overlap each other and are directed toward the optical axis 300 of the microlens as a whole. In other words, the photoelectric conversion unit 12 receives the light beam 322 and the photoelectric conversion unit 13 receives the light beam 323.

  FIG. 10A is a cross-sectional view of the focus detection pixel 312 disposed at the end of the focus detection area. As shown in FIG. 2, in the focus detection pixel 312 disposed at the end point 103 at a distance S from the screen center of the focus detection area 101, the microlens 10 (about 8 to 12 μm diameter) is disposed in front of the photoelectric conversion unit 12. Then, the shape of the photoelectric conversion unit 12 is projected forward by the microlens 10. The photoelectric conversion unit 12 is formed on the semiconductor circuit substrate 29, and the microlens 10 is integrally and fixedly formed thereon by a semiconductor image sensor manufacturing process.

  FIG. 10B is a cross-sectional view of the focus detection pixel 313 disposed at the end of the focus detection area. As shown in FIG. 2, in the focus detection pixel 313 disposed at the end point 103 at a distance S from the screen center of the focus detection area 101, the microlens 10 (about 8 to 12 μm in diameter) is disposed in front of the photoelectric conversion unit 13. Then, the shape of the photoelectric conversion unit 13 is projected forward by the microlens 10. The photoelectric conversion unit 13 is formed on the semiconductor circuit substrate 29, and the microlens 10 is integrally and fixedly formed thereon by a semiconductor image sensor manufacturing process.

  The photoelectric conversion unit 12 of the focus detection pixel 312 and the photoelectric conversion unit 13 of the focus detection pixel 313 are arranged at asymmetric positions with respect to the optical axis 300 of the microlens 10 and are cross-sections of the focus detection pixels 312 and 313. When the figures are superimposed on the basis of the optical axis 300 of the microlens 10, the photoelectric conversion units 12 and 13 are partially overlapped. Accordingly, the light beam 332 that projects the photoelectric conversion unit 12 and the light beam 333 that projects the photoelectric conversion unit 13 partially overlap each other, and as a whole, are in a direction different from the optical axis 300 of the microlens (in FIG. 10, below the optical axis 300). Direction). In other words, the photoelectric conversion unit 12 receives the light beam 332 and the photoelectric conversion unit 13 receives the light beam 333.

  FIG. 11 shows a configuration of a pupil division type phase difference detection type focus detection optical system using a microlens. In the figure, reference numeral 90 denotes a pupil plane set at a distance d in front of the microlens disposed on the planned imaging plane of the interchangeable lens 202 (see FIG. 1). In this specification, the pupil plane is referred to as a “ranging pupil plane”. . The distance d is a distance determined according to the curvature and refractive index of the microlens, the distance between the microlens and the photoelectric conversion unit, and is referred to as “distance pupil distance” in this specification. 91 is an optical axis of the interchangeable lens 202, 10a to 10d are microlenses arranged near the center of the screen, 12a, 12b, 13a and 13b are photoelectric conversion units of the microlenses 10a to 10d, and 312a, 312b, 313a and 313b are focal points. The detection pixels 72, 73, 82, and 83 are light beams for focus detection.

  Reference numeral 92 denotes an area of the photoelectric conversion units 12a and 12b projected onto the distance measurement pupil plane 90 by the microlenses 10a and 10c, and is referred to as “distance measurement pupil” in this specification. Reference numeral 93 denotes an area of the photoelectric conversion units 13a and 13b projected on the distance measuring pupil plane 90 by the microlenses 10b and 10d, that is, a distance measuring pupil. In FIG. 11, for the sake of clarity, the distance measuring pupil is shown as an elliptical area, but in reality, the shape of the photoelectric conversion unit is an enlarged projection. The distance measuring pupils 92 and 93 overlap in the vicinity of the optical axis 91.

  In FIG. 11, four focus detection pixels 312a, 312b, 313a, and 313b adjacent in the vicinity of the center of the screen are schematically illustrated, but the photoelectric conversion units correspond to the other focus detection pixels, respectively. Light beams coming from the distance measurement pupils 92 and 93 to each microlens are received. For this reason, in the focus detection pixel located away from the center of the screen, the position of the photoelectric conversion unit is asymmetrically arranged with respect to the optical axis of the microlens, and the optical axis of the interchangeable lens from the optical axis of the microlens. The light beam approaching the 91 side is received. Here, the arrangement direction of the focus detection pixels is made to coincide with the arrangement direction of the pair of distance measuring pupils, that is, the arrangement direction of the pair of photoelectric conversion units.

  The microlenses 10a to 10d are disposed in the vicinity of the planned imaging surface of the interchangeable lens 202 (see FIG. 1), and the photoelectric conversion units 12a, 12b, 13a, and 13b disposed behind the microlenses 10a to 10d. The shape is projected onto the exit pupil 90 separated from the microlenses 10a to 10d by the distance measuring pupil distance d, and the projected shape forms the distance measuring pupils 92 and 93. That is, the projection direction of the photoelectric conversion unit in each pixel is determined so that the projection shape (ranging pupils 92 and 93) of the photoelectric conversion unit of each pixel matches on the exit pupil 90 at the projection distance d.

  The photoelectric conversion unit 12a receives a light beam 72 that passes through the distance measuring pupil 92 and travels toward the micro lens 10a, and outputs a signal corresponding to the intensity of an image formed on the micro lens 10a by the light beam 72. The photoelectric conversion unit 12b receives a light beam 82 that passes through the distance measuring pupil 92 and travels toward the microlens 10c, and outputs a signal corresponding to the intensity of an image formed on the microlens 10c by the light beam 82. Similarly, the photoelectric conversion unit 13a receives a light beam 73 that passes through the distance measuring pupil 93 and travels toward the microlens 10b, and outputs a signal corresponding to the intensity of an image formed on the microlens 10b by the light beam 73. The photoelectric conversion unit 13b receives the light beam 83 that passes through the distance measuring pupil 92 and travels toward the micro lens 10d, and outputs a signal corresponding to the intensity of the image formed on the micro lens 10d by the light beam 83.

  A large number of the two types of focus detection pixels as described above are arranged in a straight line, and the output of the photoelectric conversion unit of each pixel is collected into an output group corresponding to the distance measuring pupil 92 and the distance measuring pupil 93, thereby the distance measuring pupil. Information on the intensity distribution of a pair of images formed on the pixel array by the focus detection light fluxes that respectively pass through 92 and the distance measuring pupil 93 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. By converting the image shift amount according to the opening angle of the center of gravity of the pair of distance measuring pupils, the current image plane relative to the planned image plane (corresponding to the position of the microlens array on the planned image plane) The deviation (defocus amount) of the imaging plane at the focus detection position is calculated.

  FIG. 12 is a diagram for explaining the relationship between defocus and image shift in the pupil division type phase difference detection method. In FIG. 12A, the light beam forming the image is divided into a light beam 72 passing through the distance measuring pupil 92 and a light beam 73 passing through the distance measuring pupil 93. With such a configuration, for example, when a line pattern (white line on a black background) on the optical axis 91 and perpendicular to the paper surface of FIG. 12 is imaged by the imaging optical system, the distance measuring pupil 92 on the focusing plane P0. The light beam 72 passing through and the light beam 73 passing through the distance measuring pupil 93 form a high-contrast line image pattern at the same position on the optical axis 91 as shown in FIG.

  On the other hand, on the surface P1 ahead of the focusing surface P0, the light beam 72 passing through the distance measuring pupil 92 and the light beam 73 passing through the distance measuring pupil 93 are line images blurred at different positions as shown in FIG. Form a pattern. On the surface P2 behind the focusing surface P0, the light beam 72 passing through the distance measuring pupil 92 and the light beam 73 passing through the distance measuring pupil 93 are different from FIG. 12 (b) as shown in FIG. 12 (d). Blurred line image patterns are formed at different positions in the opposite direction. Therefore, two images formed by the light beam 72 passing through the distance measuring pupil 92 and the light beam 73 passing through the distance measuring pupil 93 are detected separately, and the relative positional relationship (image shift amount) between the two images is detected. By calculating, it is possible to detect the focus adjustment state (defocus amount) of the optical system on the surface where the two images are detected.

  FIG. 13 is a diagram for explaining the relationship between the imaging pixels and the distance measuring pupil plane. In addition, the same code | symbol is attached | subjected to the element similar to the element shown in FIG. 11, and description is abbreviate | omitted. In FIG. 13, reference numeral 70 denotes a microlens disposed on the optical axis 91 of the interchangeable lens 202 shown in FIG. 1, reference numeral 71 denotes an imaging pixel constituted by the microlens 70, reference numeral 81 denotes an imaging light beam, and reference numeral 94 denotes a microlens. This is a region of the photoelectric conversion unit 71 projected by 70. Note that FIG. 13 schematically illustrates an imaging pixel (consisting of a microlens 70 and a photoelectric conversion unit 71) on the optical axis 91, but in other imaging pixels, the photoelectric conversion unit is an area 94, respectively. To receive the light flux coming to each microlens.

  The microlens 70 is disposed in the vicinity of the planned imaging plane of the imaging optical system, and the shape of the photoelectric conversion unit 71 disposed behind the microlens 70 disposed on the optical axis 91 is projected from the microlens 70. Projected onto a distance measuring pupil plane 90 separated by a distance d, and the projection shape forms an area 94. The photoelectric conversion unit 71 receives a light beam 81 that passes through the region 94 and travels toward the microlens 70, and outputs a signal corresponding to the intensity of an image formed on the microlens 70 by the light beam 81. By arranging a large number of imaging pixels as described above in a two-dimensional manner, image information can be obtained based on the output of the photoelectric conversion unit of each pixel.

  FIG. 14 is a front view showing the projection relationship on the distance measuring pupil plane. The distance measuring pupils 92 and 93 obtained by projecting the photoelectric conversion unit from the focus detection pixel to the distance measuring pupil plane 90 by the microlens are the regions 94 and 93 in which the photoelectric conversion unit is projected from the imaging pixel to the distance measuring pupil plane 90 by the microlens. Included inside. The distance measuring pupils 92 and 93 have a region 95 where a part of each other overlaps.

  FIG. 15 and FIG. 16 are diagrams for explaining the effect of superimposing the distance measuring pupil and the appropriate amount of superimposition. In the figure, a surface PF is a planned focal plane of the imaging optical system on which the image sensor is arranged. The plane PA is a distance measuring pupil plane, and is separated from the planned focal plane PF by a distance d. Further, the plane PL is an exit pupil plane of the imaging optical system, and is separated from the planned focal plane PF by a distance f. Reference numeral 91 denotes an optical axis of the imaging optical system, and a position AC is a point where the planned focal plane PF and the optical axis 91 intersect, that is, the center of the screen. Further, the position AE is a position that is separated from the screen center AC by a distance S on the planned focal plane PF, and is an end position where the focus detection pixels are arranged (see FIG. 2). Lines 70 and 72 are boundary lines indicating the open F value of the imaging optical system, that is, lines for expecting the open F value from the center of the screen.

  FIG. 15A is a diagram in the case where the distance measurement pupils are not superimposed, and a pair of light beams received by the focus detection pixels arranged at the position AC in the center of the screen are formed on the distance measurement pupil plane PA. Distribution, that is, distance measurement pupils 150 and 160, and a pair of distributions formed on the distance measurement pupil plane PA by a pair of light beams received by focus detection pixels arranged at a position AE away from the center of the screen, that is, distance measurement pupils 150 and 160 coincide with each other as shown in FIG. 15B, and there is no portion overlapping the pair of distance measuring pupils 150 and 160.

  At the position AC in the center of the screen, the focus detection pixel that receives the light beam passing through the distance measuring pupil 150 receives the light beam within the range indicated by the line 52 on the outside and the optical axis 91 on the inside in FIG. become. Further, the focus detection pixel that receives the light beam passing through the distance measuring pupil 160 at the position AC receives the light beam within the range indicated by the line 50 on the outer side and the optical axis 91 on the inner side in FIG. . On the other hand, the focus detection pixel that receives the light beam passing through the distance measuring pupil 150 at the position AE that is separated from the center of the screen by the distance S is within the range indicated by the line 62 on the outside and the line 90 on the inside in FIG. The light beam is received. Further, the focus detection pixel that receives the light beam passing through the distance measuring pupil 160 at the position AE receives the light beam within the range indicated by the line 60 on the outer side and the line 90 on the inner side in FIG.

  When the exit pupil distance f of the imaging optical system matches the distance measurement pupil distance d, as shown in FIG. 15B, the result of the pair of distance measurement pupils 150 and 160 on the distance measurement pupil plane PA is obtained. The light beam passing through the circle 170 indicating the open F value of the image optical system is received by the focus detection pixels arranged from the position AC to the position AE, and the intensity level is set by the pair of light beams having the same light amount. Since a pair of aligned images is formed, the image shift amount of the pair of images can be detected with high accuracy based on the output of the focus detection pixels.

  When the exit pupil distance f of the imaging optical system is different from the distance measurement pupil distance d (d> f in FIG. 15A), the light flux passing through the distance measurement pupils 150 and 160 is received at the position AC in the center of the screen. As shown in FIG. 15C, the focus detection pixel includes an exit pupil among the light beams that pass through the distributions 151 and 161 formed on the exit pupil plane PL by the light beams that pass through the pair of distance measurement pupils 150 and 160. The light beam passing through the inside of the circle 171 indicating the open F value of the imaging optical system on the surface PL is received. As a result, at a position AC in the center of the screen, a pair of images having the same intensity level is formed by a pair of light beams having the same light amount, and the image shift amount of the pair of images is detected with high accuracy based on the output of the focus detection pixels. be able to.

  However, the focus detection pixel that receives the light beam passing through the distance measurement pupils 150 and 160 at the position AE at the end of the focus detection area, as shown in FIG. 15D, the light beam that passes through the pair of distance measurement pupils 150 and 160. Among the light beams passing through the distributions 152 and 162 formed on the exit pupil plane PL, the light beam passing through the inside of the circle 171 indicating the open F value of the imaging optical system on the exit pupil plane PL is received. In this case, as apparent from FIG. 15 (d), the common region of the distribution 152 and the circle 171 disappears, so that at the position AE at the end of the focus detection area, a pair of images for detecting the image shift amount. An image is not formed, and focus detection becomes impossible. In addition, a pair of images is formed between the position AC and the position AE, but the light amount balance between the pair of images formed in the portion close to the position AE is greatly broken, so that the detection accuracy of the image shift amount is lowered. .

  Next, FIG. 16A is a diagram in the case where the distance measuring pupil is superimposed, and a pair of light beams received by the focus detection pixel arranged at the position AC in the center of the screen is formed on the distance measuring pupil plane PA. A pair of distributions formed by the focus detection pixels PA and the distance detection pupils 250 and 260 and a pair of light beams received by the focus detection pixels arranged at the position AE away from the center of the screen on the distance measurement pupil plane PA. That is, the distance measurement pupils 250 and 260 coincide with each other as shown in FIG. 16B, and the pair of distance measurement pupils 250 and 260 has an overlapping portion (hatched portion in the drawing) 240.

  At the position AC in the center of the screen, the focus detection pixel that receives the light beam passing through the distance measuring pupil 250 receives the light beam within the range indicated by the line 52 on the outer side and the line 53 on the inner side in FIG. Become. Further, the focus detection pixel that receives the light beam passing through the distance measuring pupil 260 at the position AC receives the light beam within the range indicated by the line 50 on the outer side and the line 51 on the inner side in FIG. On the other hand, the focus detection pixels that receive the light beam passing through the distance measuring pupil 250 at the position AE that is separated from the center of the screen by the distance S are within the range indicated by the line 62 on the outside and the line 63 on the inside in FIG. The light beam is received. Further, the focus detection pixel that receives the light beam passing through the distance measuring pupil 260 at the position AE receives the light beam within the range indicated by the line 60 on the outer side and the line 61 on the inner side in FIG.

  When the exit pupil distance f of the imaging optical system matches the distance measuring pupil distance d, as shown in FIG. 16 (b), the light flux passing through the pair of distance measuring pupils 250 and 260 on the distance measuring pupil plane PA is shown. The light flux passing through the inside of the circle 170 indicating the open F value of the imaging optical system is received by the focus detection pixels arranged from the position AC to the position AE. Since a pair of images with uniform intensity levels are formed, the image shift amount of the pair of images can be detected with high accuracy based on the output of the focus detection pixels.

  When the exit pupil distance f of the imaging optical system is different from the distance measurement pupil distance d (d> f in FIG. 16A), the light flux passing through the distance measurement pupils 150 and 160 is received at the position AC in the center of the screen. As shown in FIG. 16C, the focus detection pixel has an exit pupil out of the light fluxes passing through the distributions 251 and 261 formed by the light fluxes passing through the pair of distance measuring pupils 250 and 260 on the exit pupil plane PL. A light beam passing through the inside of a circle 171 indicating the open F value of the imaging optical system on the surface PL is received, and a pair of images having the same intensity level by a pair of light beams having the same light amount at the position AC in the center of the screen. Therefore, it is possible to detect the image shift amount of the pair of images with high accuracy based on the output of the focus detection pixels.

  As shown in FIG. 16D, the focus detection pixels that receive the light beams passing through the distance measurement pupils 250 and 260 at the position AE at the focus detection area end emit light beams that pass through the pair of distance measurement pupils 250 and 260, respectively. Of the luminous fluxes passing through the distributions 252 and 262 formed on the pupil plane PL, the luminous flux passing through the inside of the circle 171 indicating the open F value of the imaging optical system is received on the exit pupil plane PL. In this case, as apparent from FIG. 16 (d), the distribution 252 is enlarged toward the optical axis 91, so that a common area with the circle 171 can be secured, and the light amount is also obtained at the position AE at the end of the focus detection area. A pair of images that are not significantly out of balance are formed, and focus detection can be performed while maintaining focus detection accuracy. Similarly, focus detection can be performed while maintaining focus detection accuracy in the focus detection pixels arranged from the position AC to the position AE. It is desirable to improve the light quantity balance (light quantity ratio) of a pair of images at a position AE away from the center of the screen by overlapping the distance measuring pupil so that it is 1: 4 or more, preferably 1: 2 or more.

  Although FIG. 16 illustrates the case of the imaging optical system in which the exit pupil distance f is shorter than the distance measuring pupil distance d, the distance measuring pupil is also used in the case of the imaging optical system in which the exit pupil distance f is longer than the distance measuring pupil distance d. By partially overlapping, it is possible to ensure focus detection accuracy around the screen. In this way, by partially overlapping the distance measuring pupil (the light quantity distribution of the pair of light beams on the distance measuring pupil plane), it is possible to focus on the periphery of the screen with respect to the imaging optical system having various exit pupils and open F values. Detection is possible.

  Note that the amount of distance measurement pupil superimposition is limited as follows. When only the overlapping portion of the distance measuring pupil enters the circle showing the open F value of the imaging optical system on the exit pupil plane PL, the centroids of the pair of light beams coincide with each other. The pair of images is not shifted from each other, and focus detection becomes impossible. In order to prevent this, the overlapping amount of the distance measuring pupil is limited so that the distance measuring pupil part other than the overlapping part of the pair of distance measuring pupils enters the inside of the open F value. The barycentric positions of the light quantity distributions of the pair of light beams passing through the pair of distance measuring pupils are made different.

  For example, in FIG. 16B, by making the width of the overlapping portion 240 shorter than the diameter of the circle 170, the center of gravity position 253 of the common portion of the circle 170 and the distance measuring pupil 250 and the common portion of the circle 170 and the distance measuring pupil 260 are obtained. Is separated from the center of gravity position 263 by a distance G1 on the distance measuring pupil plane PA. In FIG. 16C, the width of the overlapping portion 241 is shorter than the diameter of the circle 171, the barycentric position 254 of the common part of the circle 171 and the light quantity distribution 251, and the barycentric position of the common part of the circle 171 and the light quantity distribution 261. H.264 is separated from the exit pupil plane PL by a distance G2. Further, in FIG. 16D, the center of gravity position 255 of the common part of the circle 171 and the light quantity distribution 252 and the center of gravity position 264 of the common part of the circle 171 and the light quantity distribution 262 are separated by a distance G3 on the exit pupil plane PL. ing.

  In general, assuming an open F value with the smallest aperture diameter, the difference in the center of gravity of the light distribution of the pair of distance measuring pupils that falls within the circle of the open F value on the distance measuring pupil plane PA (FIG. 16B). ) (Corresponding to G1)), the value obtained by dividing the distance measurement pupil distance d (= distance measurement F value) is set to be smaller than the F value necessary to maintain the predetermined focus detection accuracy. The distance measurement F value is a conversion coefficient for converting the detected image shift amount into the defocus amount of the imaging optical system. If this value is large, the focus detection accuracy (= accuracy of the calculated defocus amount) decreases. To do.

  For example, when an interchangeable lens having a bright imaging optical system with an open F value of F5.6 or higher is used as a standard for an interchangeable lens that can be applied to a focus detection system, the distance measurement F value at the open F value of 5.6 is F20 or higher. Thus, the overlapping amount of the distance measuring pupils, that is, the difference in the center of gravity position can be defined.

  Further, the distance measurement pupil distance d of the distance measurement pupil plane PA is set so as to match the average position of the exit pupil of the imaging optical system built in a plurality of types of interchangeable lenses applicable to the focus detection system. By doing so, it is possible to relax the restrictions caused by the above-mentioned open F value, and focus detection according to the present invention for an interchangeable lens group in which the exit pupil distance is dissipated in a wider range or a lens group with a darker open F value. The system can be applied, and the focus detectable area on the screen can be expanded to the periphery.

  Here, an example of the overlapping amount of the distance measuring pupil will be described. Distance pupil distance d is 100 mm, light quantity distribution of a pair of light fluxes is uniform, aperture shape of the aperture stop is square (when it is circular, the calculation of the position of the center of gravity becomes complicated, so here it is square), distance measurement pupil Assuming that the aperture width (length of one side of the square) of the open aperture converted on the surface is 18 mm (equivalent to F5.6), in order to set the difference in the center of gravity of the pair of light beams to 5 mm (equivalent to F20), measurement is required. What is necessary is just to superimpose 8 mm of light quantity distribution of a pair of light beam on a distance pupil. If the projection magnification of the microlens constituting the focus detection pixel (the magnification at which the photoelectric conversion unit is projected onto the distance measuring pupil plane) is 10,000, the amount of superposition in the photoelectric conversion unit is 0.8 microns.

  FIG. 17 is a flowchart showing the operation of the digital still camera (imaging device) shown in FIG. The body drive control device 214 starts this operation when a power switch (not shown) of the camera is turned on in step 100. In step 110, the subject brightness is detected based on the output signal level of the image sensor 212, and the exposure time of the image sensor 212 is controlled according to the subject brightness. In subsequent step 120, data of the imaging pixels and focus detection pixels of the imaging device 212 are read. In step 130, the image pickup pixel data is displayed on the electronic viewfinder.

  In step 140, an image shift detection calculation process (correlation calculation process) to be described later is performed based on a pair of image data of the focus detection pixels to calculate a defocus amount. In the following step 150, it is determined whether or not the focus is close, that is, whether the absolute value of the defocus amount is within a predetermined value. If it is determined that the in-focus state is not achieved, the process proceeds to step 160, the defocus amount is transmitted to the lens drive control unit 206, the focusing lens 210 of the interchangeable lens 202 is driven to the in-focus position, and the process returns to step 110 to return to the above-described state. Repeat the operation. Even when focus detection is impossible, the process branches to this step, a scan drive command is transmitted to the lens drive control device 206, and the focusing lens 210 of the interchangeable lens 202 is driven to scan from infinity to the nearest position. Return and repeat the above operation.

  On the other hand, if it is determined that it is close to the in-focus state, the process proceeds to step 170 to determine whether or not a shutter release has been performed by operating a shutter button (not shown), and if not, the process returns to step 110 and described above. Repeat the operation. If the shutter release operation has been performed, the process proceeds to step 180, the shooting parameters are determined according to the subject brightness, the aperture control information is transmitted to the lens drive control unit 206, and the aperture value of the interchangeable lens 202 is set to the shooting aperture value. When the aperture control is completed, the image sensor 212 is exposed according to the determined charge accumulation time.

  In step 190, data of the imaging pixel is read from the imaging device 212, and in step 200, image data at the focus detection pixel position is obtained by interpolation based on the data of the imaging pixel around the focus detection pixel. The entire image data is generated. In step 210, the image data is stored in the memory card 219, and the process returns to step 110 to repeat the above-described operation.

The details of the image shift detection calculation process (correlation calculation process, phase difference detection process) executed in step 140 of FIG. 17 will be described with reference to FIG. Since the pair of images detected by the focus detection pixels may be out of balance in the light amount, a correlation calculation process that can maintain the image shift detection accuracy with respect to the light amount balance as described later is performed. A pair of data strings (α1 to αM, β1 to βM, where M is the number of data) output from the focus detection pixel column is subjected to a high frequency cut filter process as shown in Formula (1), and the first data string and By generating the second data string (A1 to AN, B1 to BN), noise components and high frequency components that adversely affect the correlation process are removed from the data string. It should be noted that this processing can be omitted when the calculation time is shortened or when it is already defocused and it is known that there are few high frequency components.
An = αn + 2 × αn + 1 + αn + 2,
Bn = βn + 2 × βn + 1 + βn + 2 (1)
In the formula (1), n = 1 to N.

Correlation calculation processing shown in equation (2) is performed on the data strings An and Bn to calculate the correlation amount C (k).
C (k) = Σ | An × Bn + 1 + k−Bn + k × An + 1 | (2)
In equation (2), the Σ operation is accumulated for n, and the range taken by n is limited to a range in which data of An, An + 1, Bn + k, and Bn + 1 + k exist according to the shift amount k. . The shift amount k is an integer and is a relative shift amount with the data interval of the data string as a unit. As shown in FIG. 18A, the calculation result of the expression (2) shows that the correlation amount C (k) is minimal in the shift amount with high correlation between the pair of data (k = kj = 2 in FIG. 18A). (The smaller the value, the higher the degree of correlation).

Next, the shift amount x that gives the minimum value C (x) with respect to the continuous correlation amount is obtained by using the three-point interpolation method according to the equations (3) to (6).
x = kj + D / SLOP (3),
C (x) = C (kj) − | D | (4),
D = {C (kj-1) -C (kj-1)} / 2 (5),
SLOP = MAX {C (kj + 1) -C (kj), C (kj-1) -C (kj)} (6)

  Whether or not the shift amount x calculated by the equation (3) is reliable is determined as follows. As shown in FIG. 18B, when the degree of correlation between a pair of data is low, the value of the minimal value C (x) of the interpolated correlation amount is large. Accordingly, when C (x) is equal to or greater than a predetermined threshold value, it is determined that the calculated shift amount has low reliability, and the calculated shift amount x is canceled. Alternatively, in order to normalize C (x) with the contrast of data, when the value obtained by dividing C (x) by SLOP that is proportional to the contrast is equal to or greater than a predetermined value, the reliability of the calculated shift amount Is determined to be low, and the calculated shift amount x is canceled. Alternatively, when SLOP that is a value proportional to the contrast is equal to or less than a predetermined value, it is determined that the subject has low contrast and the reliability of the calculated shift amount is low, and the calculated shift amount x is canceled.

  As shown in FIG. 18C, when the correlation between the pair of data is low and there is no drop in the correlation amount C (k) between the shift ranges kmin to kmax, the minimum value C (x) is obtained. In such a case, it is determined that the focus cannot be detected.

When it is determined that the calculated shift amount x is reliable, the defocus amount DEF of the subject image plane with respect to the planned image formation plane can be obtained by Expression (7).
DEF = FA · PY · x (7)
In Expression (7), PY is a detection pitch (the pitch of focus detection pixels), and FA is a distance measurement F value (conversion coefficient).

<< Modification of Embodiment of Invention >>
FIG. 19 is a front view showing a detailed configuration of an image sensor 212A according to a modification, and shows an enlarged vicinity of the focus detection area. In the figure, the vertical and horizontal directions of the image sensor 212A correspond to the vertical and horizontal directions of the screen shown in FIG. The image sensor 212 shown in FIG. 3 is composed of a pair of focus detection pixels 312 and 313 shown in FIGS. 5 (a) and 5 (b). On the other hand, in the imaging device 212A of the modification shown in FIG. 19, the focus detection pixel has a pixel structure including a pair of photoelectric conversion units under one microlens.

  The image sensor 212 </ b> A includes an imaging pixel 310 and a focus detection pixel 311. As shown in FIG. 20, the focus detection pixel 311 includes a microlens 10 and a pair of photoelectric conversion units 22 and 23. The photoelectric conversion units 22 and 23 are designed in such a shape that the microlens 10 receives all light beams that pass through a predetermined region (for example, F2.8) of the exit pupil of the interchangeable lens 202. The photoelectric conversion units 22 and 23 are arranged in the horizontal direction. The left part of the photoelectric conversion unit 22 and the right part of the photoelectric conversion unit 23 have a region 24 where sensitivity distributions overlap. The focus detection pixels 311 are arranged in the horizontal direction (alignment direction of the photoelectric conversion units 22 and 23).

  FIG. 21 shows a cross section of the focus detection pixel 311. FIG. 21A is a cross-sectional view of the focus detection pixel 311 arranged in the vicinity of the position AC shown in FIG. 2, and the microlens 10 is arranged in front of the focus detection photoelectric conversion units 22 and 23. The lens 10 projects the photoelectric conversion units 22 and 23 forward. The photoelectric conversion units 22 and 23 are formed on the semiconductor circuit substrate 29. The sensitivity superimposing portion 24 is on the optical axis of the microlens 10, and the photoelectric conversion units 22 and 23 receive the focus detection light beam coming from the direction around the optical axis of the microlens 10 as a whole.

  FIG. 21B is a cross-sectional view of the focus detection pixel 311 arranged in the vicinity of the position AE shown in FIG. 2. The microlens 10 is arranged in front of the focus detection photoelectric conversion units 22 and 23. The photoelectric conversion units 22 and 23 are projected forward by the microlens 10. The photoelectric conversion units 22 and 23 are formed on the semiconductor circuit substrate 29. The sensitivity superimposing portion 24 is not on the optical axis of the microlens 10, and the photoelectric conversion units 22 and 23 receive the focus detection light beam coming from the direction closer to the optical axis of the optical system than the optical axis of the microlens 10 as a whole.

  A focus detection method by a pupil division method using a microlens will be described with reference to FIG. The basic principle is the same as the focus detection method described in FIG. In the figure, focus detection pixels (consisting of a microlens 50 and a pair of photoelectric conversion units 52 and 53) on the optical axis 91 and adjacent focus detection pixels are schematically illustrated, but other focus detections are illustrated. Also in the pixel for use, each of the pair of photoelectric conversion units receives the light flux that arrives at each microlens from the pair of distance measuring pupils. The arrangement direction of the focus detection pixels is made to coincide with the arrangement direction of the pair of distance measuring pupils 92 and 93, that is, the arrangement direction of the pair of photoelectric conversion units. The distance measuring pupils 92 and 93 partially overlap each other.

  The microlens 50 is disposed in the vicinity of the planned imaging surface of the imaging optical system, and the shape of the pair of photoelectric conversion units 22 and 23 disposed behind the microlens 50 disposed on the optical axis 91 is micro. The projection is performed on the exit pupil plane 90 separated from the lens 50 by the projection distance d, and the projection shape forms distance measuring pupils 92 and 93. The photoelectric conversion unit 22 outputs a signal corresponding to the intensity of the image formed on the microlens 50 by the focus detection light beam 42 that passes through the distance measuring pupil 92 and faces the microlens 50. Further, the photoelectric conversion unit 23 outputs a signal corresponding to the intensity of the image formed on the microlens 50 by the focus detection light beam 43 that passes through the distance measuring pupil 93 and faces the microlens 50.

  A large number of such focus detection pixels are arranged in a straight line, and the output of the pair of photoelectric conversion units of each pixel is grouped into an output group corresponding to the distance measurement pupil 92 and the distance measurement pupil 93, whereby the distance measurement pupil 92 and Information on the intensity distribution of the pair of images formed on the focus detection pixel array by the focus detection light fluxes that respectively pass through the distance measuring pupil 93 is obtained.

  FIG. 23 is a sectional view showing the detailed structure of the focus detection pixel. FIG. 23 is a cross-sectional view showing a detailed structure of a focus detection pixel having a pair of photoelectric conversion units behind one microlens. The focus detection light beam is condensed on the semiconductor substrate 29 by the microlens 10. An oxide film having an opening is formed on the semiconductor substrate 29 to shield light other than the light receiving region. The semiconductor substrate 29 is a p-type semiconductor, and a pair of n-type regions 32 and 33 are formed in the light receiving region. The region 34 between the pair of n-type regions 32 and 33 is a p-type region as it is without providing an isolation region.

  In such a structure, a PN junction is formed by the n-type regions 32 and 33 and the p-type substrate to constitute a pair of photoelectric conversion units (photodiodes). The charge generated by the light beam incident on the region 34 flows into the n-type region 32 or the n-type region 33 by diffusion. As a result, the photosensitivity distributions 34 and 35 of the n-type region 32 and the n-type region 33 overlap in the region 34.

  FIG. 24 is a diagram illustrating a configuration of an imaging apparatus 201A according to a modification. In the imaging apparatus 201 shown in FIG. 1, the example in which the imaging element 211 is used for both focus detection and imaging is shown. However, in the imaging apparatus 201A of this modification, as shown in FIG. A dedicated focus detection element 211 is provided. The camera body 203 is provided with a half mirror 221 for separating a photographing light beam, an imaging element 212 dedicated for imaging on the transmission side, and a focus detection element 211 dedicated for focus detection on the reflection side.

  Before photographing, focus detection is performed according to the output of the focus detection element 211. At the time of release, image data corresponding to the output of the imaging element 212B dedicated to imaging is generated. The half mirror 221 may be a total reflection mirror, and may be retracted from the photographing optical path during photographing. It is also possible to reverse the arrangement of the focus detection element 211 and the imaging element 212B, arrange the imaging element 212B dedicated to imaging on the reflection side, and arrange the imaging element 211 for focus detection and electronic viewfinder display on the transmission side.

  In the embodiment described above, an area obtained by projecting the shape of the photoelectric conversion unit on the distance measuring pupil plane by the microlens is used as the distance measuring pupil, and the distance measuring pupils 92 and 93 have a clear periphery as shown in FIG. Actually, the surrounding shape of the distance measuring pupil is slightly blurred due to the influence of aberration and diffraction of the microlens, and the distance measuring pupil is based on the distribution indicating the proportion of the light beam passing through the distance measuring pupil. It is prescribed.

  Note that the number of focus detection areas and their positions are not limited to the arrangement shown in FIG. A plurality of focus detection areas can be arranged by arranging focus detection pixels in a horizontal or vertical direction at a plurality of arbitrary positions in the screen.

  In the image sensor shown in FIGS. 3 and 19, the example in which the focus detection pixels are arranged without gaps in the focus detection area is shown. However, the focus detection pixels may be arranged every several pixels. The focus detection accuracy is slightly reduced by increasing the pitch of the focus detection pixels, but the density of the focus detection pixels is reduced, so that the image quality after image interpolation is improved.

  In the image pickup device shown in FIGS. 3 and 19, the example in which the imaging pixels and the focus detection pixels are arranged in a dense square lattice arrangement is shown, but they may be arranged in a dense hexagonal lattice arrangement.

  In the imaging device shown in FIGS. 3 and 19, an example in which the imaging pixels include a Bayer color filter is shown, but the configuration and arrangement of the color filter are not limited to this, and the complementary color filter (green: G, yellow: Ye, magenta: Mg, cyan: Cy) may be employed. The focus detection pixels are arranged at pixel positions where cyan and magenta (including a blue component whose output error is relatively inconspicuous) should be arranged.

  In the above-described embodiment, the focus detection pixel data is not used as image data, but the dynamic range may be expanded by combining the focus detection pixel data with the image data of the image sensor as a luminance signal.

  In the above-described embodiment, the focus detection pixel data is used for focus detection, but can also be used as photometric data for exposure control of the image sensor. In this way, the photometric sensor can be omitted.

  In the above-described embodiment, the focus detection pixel data is used for focus detection, but it can also be used as blur detection data for image blur detection of the image sensor. In this way, an image sensor dedicated to image blur detection can be omitted.

  In the above-described embodiment, the focus detection pixel data is used for image shift focus detection, but can also be used as contrast detection data.

  In the above-described embodiment, the spectral sensitivity of the focus detection pixel has a characteristic close to white as shown in FIG. 7, but the sensitivity of the focus detection pixel is one of the spectral sensitivities shown in FIG. It is good. Further, focus detection pixels having different spectral sensitivities may coexist in one focus detection element.

  In the above-described embodiment, the distance detection pupil plane set by the focus detection pixels is single, but a plurality of types of focus detection pixels corresponding to a plurality of distance measurement pupil planes having different distance detection pupil distances. May be provided.

  In the above-described embodiment, the image data of the imaging pixels is not used for focus detection, but is used as focus detection data for the contrast detection method, and the focus detection result and contrast of the pupil division method using the focus detection pixels. You may make it use together the focus detection result by a system.

  In the image pickup apparatus 201A of the modified example shown in FIG. 24, the light beam is split by the half mirror 221 so as not to depend on the wavelength, but the light beam can also be split by a spectroscopic mirror. For example, a mirror that divides into an infrared light component and a visible light component is received, the visible light component is received by the image sensor, the infrared light component is received by the focus detection element, and the focus detection result of the focus detection element is converted into the infrared light. By correcting according to the amount of aberration, the focus detection result of visible light can be corrected and used. In this way, it is possible to prevent the amount of visible light received by the image sensor from being reduced by the half mirror.

  In the image pickup apparatus 201A of the modified example shown in FIG. 24, the half mirror 221 may be formed of a multilayer film, or a polarizing mirror (for example, a polarization component that reflects a polarization component parallel to the paper surface of FIG. It may be formed as a transparent).

  In the embodiment described above, the lens built in the interchangeable lens side is moved in the optical axis direction for focus adjustment, but the image sensor in the camera body may be moved in the optical axis direction, The focus may be adjusted roughly by moving the lens in the optical axis direction, and the focus may be finely adjusted by moving the image sensor.

  The present invention is not limited to an image pickup element and a focus detection element having focus detection pixels of a pupil division type phase difference detection method using a microlens, and focus detection pixels of another type of pupil division type phase difference detection method are used. The present invention can be applied to an imaging element and a focus detection element that have the same. For example, the present invention can be applied to an image pickup element and a focus detection element having focus detection pixels of a pupil division type phase difference detection method using polarized light, and a pupil division type phase difference detection method using a re-imaging lens. .

  In the above-described embodiment, the image sensor and the focus detection element may be a CCD image sensor or a CMOS image sensor.

  The imaging device is not limited to a digital still camera including a camera body provided with a removable interchangeable lens. It can also be applied to lens-integrated digital still cameras and video cameras. Alternatively, the present invention can be applied to a small camera module or a surveillance camera built in a mobile phone or the like. The present invention can also be applied to focus detection devices other than cameras, distance measuring devices, and stereo distance measuring devices.

Cross-sectional view showing a configuration of a camera according to an embodiment The figure which shows arrangement | positioning of the focus detection pixel on an imaging | photography screen. Front view showing detailed configuration of image sensor The figure which shows the structure of the pixel for imaging The figure which shows the structure of the pixel for focus detection Diagram showing spectral sensitivity characteristics of green, red and blue pixels for imaging The figure which shows the spectral sensitivity characteristic of the pixel for focus detection Cross-sectional view of imaging pixels Cross section of focus detection pixel Cross section of focus detection pixel The figure which shows the structure of the focus detection optical system of the pupil division type phase difference detection method using a micro lens Diagram for explaining the relationship between defocus and image shift in the pupil division type phase difference detection method The figure for demonstrating the relationship between the pixel for imaging, and a ranging pupil plane Front view showing the projection relationship on the distance measurement pupil plane Diagram for explaining the effect of focusing on the distance measurement pupil and the appropriate amount of superposition Diagram for explaining the effect of focusing on the distance measurement pupil and the appropriate amount of superposition Flow chart showing operation of digital still camera (imaging device) The figure explaining the detail of image shift detection calculation processing (correlation calculation processing, phase difference detection processing) Front view showing a detailed configuration of an image sensor of a modification Front view showing a detailed configuration of an image sensor of a modification The figure which shows the cross section of the pixel for focus detection The figure explaining the focus detection method by the pupil division method using a micro lens Sectional drawing which shows the detailed structure of the pixel for focus detection The figure which shows the structure of the imaging device of a modification

Explanation of symbols

10 Microlens 11, 12, 13, 22, 23 Photoelectric conversion unit 24 Overlapping area 201, 201A Digital still camera 202 Interchangeable lens 206 Lens drive control device 212, 212A, 212B Image sensor 310 Imaging pixels 311, 312, 313 Focus Pixel 214 for detection Body drive control device

Claims (4)

In an imaging device that can be mounted by exchanging a plurality of types of imaging optical systems with different exit pupil distances, the imaging optical system is disposed on a predetermined focal plane and receives a pair of light beams passing through the imaging optical system. A focus detection element in which a plurality of first focus detection pixels and a plurality of second focus detection pixels are arranged to output a pair of image signals used for phase difference detection for detecting the focus detection adjustment state of the imaging optical system ; ,
Focus detection calculation means for detecting a focus adjustment state of the imaging optical system based on output signals of the plurality of first focus detection pixels and the plurality of second focus detection pixels,
The first focus detection pixel includes a first microlens and a first photoelectric conversion unit that receives light via the first microlens, and the first photoelectric conversion unit has a predetermined distance from the planned focal plane ( Receiving a light beam passing through a first region set in common to all the first focus detection pixels on a pupil plane (referred to as a distance measurement pupil plane) set to a distance measurement pupil distance);
The second focus detection pixel includes a second microlens that is different from the first microlens and a second photoelectric conversion unit that receives light via the second microlens, and the second photoelectric conversion unit includes the second photoelectric conversion unit, Receiving a light beam passing through a second region different from the first region set in common to all the second focus detection pixels on the distance measuring pupil plane;
The distance measuring pupil distance is an average distance of exit pupil distances of the plurality of types of imaging optical systems,
The first region and the second region include a third region including the optical axis of the imaging optical system as a common region, and the third region in a direction connecting the centroid of the first region and the centroid of the second region. The width of the region is set shorter than the diameter of the region where the light beam having the largest F value among the open F values of the plurality of types of imaging optical systems passes through the distance measuring pupil plane,
The first focus detection pixels and the second focus detection pixels are alternately arranged along a straight line connecting the centroid of the first region and the centroid of the second region ,
The plurality of first focus pixels output a first signal data string, and the plurality of second focus pixels output a second signal data string,
The focus detection calculation unit multiplies the first data in the first signal data string and the data in the vicinity of the second data corresponding to the first data in the second signal data string. The first calculation data is calculated, and the second data in the second signal data string and the vicinity of the first data corresponding to the second data in the first signal data string are calculated. The second calculation data is calculated by multiplying the data, the degree of correlation between the first calculation data and the second calculation data is calculated, and the defocus amount is calculated based on the correlation amount. Focus detection device. The focus detection apparatus according to claim 1,
The largest F value among the open F values of the plurality of types of imaging optical systems is F5.6, and the first F limited by the exit pupil of the imaging optical system whose open F value is F5.6. The width of the third region is determined so that a value obtained by dividing the distance measurement pupil distance by the distance between the centers of gravity of the first region and the second region (hereinafter referred to as a distance measurement F value) is F20 or more. Feature focus detection device . The focus detection apparatus according to claim 1 or 2,
A third focus detection pixel that receives a pair of light beams passing through the imaging optical system and outputs a pair of image signals used for phase difference detection for detecting a focus detection adjustment state of the imaging optical system; A plurality of four-focus detection pixels are further arranged,
A focus detection apparatus, wherein a distance measurement pupil distance related to the third focus detection pixel and the fourth focus detection pixel is different from the distance measurement pupil distance related to the first focus detection pixel and the second focus detection pixel . A focus detection apparatus according to claim 1 ;
Focus adjusting means for adjusting the focus of the imaging optical system based on the defocus amount calculated by the focus detection calculating means;
An image pickup apparatus comprising: an image pickup device that picks up an image formed by the imaging optical system.

Images