Patent Publication Number: US-10321044-B2

Title: Image pickup apparatus and image pickup system with point image intensity distribution calculation

Description:
This is a divisional of U.S. patent application Ser. No. 14/969,630, filed Dec. 15, 2015. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an image pickup apparatus and an image pickup system. 
     Description of the Related Art 
     There have been proposed a focus detection apparatus and an optical system that are configured to perform focus detection correction based on information representing a light-flux distribution and information on an aperture of an imaging optical system. 
     In Japanese Patent Application Laid-Open No. 2007-121896, it is disclosed that a conversion coefficient for converting a shift amount of a pair of images into a defocus amount of an imaging optical system is calculated based on information representing a light-flux distribution and information on an aperture of the imaging optical system. 
     Further, there have been proposed an image pickup apparatus and an image pickup system that are configured to perform focus detection correction and image processing based on a point image intensity distribution calculated in advance. 
     In Japanese Patent Application Laid-Open No. 2013-171251, it is disclosed that a predetermined offset amount is acquired. The predetermined offset amount is determined based on a difference in shape of a pair of images generated by a pair of light fluxes passing through an exit pupil, which is caused by aberration of a photographing optical system. 
     In Japanese Patent Application Laid-Open No. 2014-7493, it is described that whether or not to perform image restoration processing on an input image is determined based on a photographing state. In Japanese Patent Application Laid-Open No. 2014-7493, an image restoration filter is acquired, and the image restoration processing is performed on the input image, only when determination to perform the image restoration processing is made. 
     SUMMARY OF THE INVENTION 
     According to one aspect of an embodiment, an image pickup apparatus, includes a point image intensity distribution generating unit configured to generate a point image intensity distribution based on lens light field data and a sensor light-receiving intensity characteristic, the lens light field data including information relating to directions of a plurality of light fluxes emitted from one point of an object position and passing through different regions of an exit pupil of an imaging optical system; and information relating to positions of points on the plurality of light fluxes, the sensor light-receiving intensity characteristic representing light-receiving intensities, which are determined on a light receiving surface of an image pickup element, of light fluxes passing through respective regions of an entrance pupil of a microlens arranged over the image pickup element. 
     According to another aspect of the embodiment, an image pickup system, includes a lens light field data storage unit configured to store lens light field data including information relating to directions of a plurality of light fluxes emitted from one point of an object position and passing through different regions of an exit pupil of an imaging optical system, and information relating to positions of points on the plurality of light fluxes; a sensor light-receiving intensity characteristic storage unit configured to store a sensor light-receiving intensity characteristic representing light-receiving intensities, which are determined on a light receiving surface of an image pickup element, of light fluxes passing through respective regions of an entrance pupil of a microlens arranged over the image pickup element; and a point image intensity distribution generating unit configured to generate a point image intensity distribution based on the lens light field data and the sensor light-receiving intensity characteristic. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram for illustrating a schematic configuration of an image pickup apparatus according to a first embodiment of the present invention. 
         FIG. 2  is a plan view for illustrating a part of an image pickup element to be used in the image pickup apparatus according to the first embodiment of the present invention. 
         FIG. 3A  and  FIG. 3B  are respectively a plan view and a sectional view for illustrating a pixel portion of the image pickup element. 
         FIG. 4  is a schematic diagram for illustrating a relationship between an exit pupil and the pixel portion. 
         FIG. 5  is a schematic diagram for illustrating a relationship between the exit pupil and the image pickup element. 
         FIG. 6  is a flow chart for illustrating an overview of processing of an auto-focus operation of the image pickup apparatus according to the first embodiment of the present invention. 
         FIG. 7  is a flow chart for illustrating focus detection processing in the image pickup apparatus according to the first embodiment of the present invention. 
         FIG. 8  is a diagram for illustrating a relationship between a defocus amount and an image shift amount. 
         FIG. 9A ,  FIG. 9B , and  FIG. 9C  are schematic diagrams for describing shading. 
         FIG. 10  is a graph for showing frequency characteristics of a filter. 
         FIG. 11A ,  FIG. 11B , and  FIG. 11C  are diagrams for describing a point image intensity distribution. 
         FIG. 12A ,  FIG. 12B ,  FIG. 12C ,  FIG. 12D , and  FIG. 12E  are diagrams for illustrating point image intensity distributions. 
         FIG. 13  is a flow chart for illustrating point image intensity distribution generation processing of the image pickup apparatus according to the first embodiment of the present invention. 
         FIG. 14  is a diagram for illustrating a relationship among lens light field data, a sensor light-receiving intensity characteristic, and a point image intensity distribution. 
         FIG. 15A ,  FIG. 15B ,  FIG. 15C ,  FIG. 15D ,  FIG. 15E , and  FIG. 15F  are schematic diagrams for illustrating the sensor light-receiving intensity characteristic. 
         FIG. 16  is a graph for showing difference in sensor light-receiving intensity characteristic due to difference in type of the image pickup element. 
         FIG. 17A  and  FIG. 17B  are schematic diagrams for illustrating influences on the sensor light-receiving intensity characteristic due to misalignment caused when the image pickup element is mounted. 
         FIG. 18A ,  FIG. 18B , and  FIG. 18C  are schematic diagrams for two-dimensionally illustrating the lens light field data. 
         FIG. 19A  and  FIG. 19B  are schematic diagrams for illustrating a relationship between presence or absence of aberration and collection of light fluxes. 
         FIG. 20A ,  FIG. 20B , and  FIG. 20C  are schematic diagrams for illustrating a method of forming the lens light field data. 
         FIG. 21  is a flow chart for illustrating defocus amount correction processing of the image pickup apparatus according to the first embodiment of the present invention. 
         FIG. 22A ,  FIG. 22B , and  FIG. 22C  are schematic diagrams for illustrating the point image intensity distributions. 
         FIG. 23  is a schematic diagram for illustrating contrast evaluation values. 
         FIG. 24A ,  FIG. 24B ,  FIG. 24C ,  FIG. 24D ,  FIG. 24E ,  FIG. 24F ,  FIG. 24G ,  FIG. 24H ,  FIG. 24I , and  FIG. 24J  are schematic diagrams for illustrating a defocus offset generation principle. 
         FIG. 25  is a schematic diagram for illustrating a configuration of an image pickup system according to a second embodiment of the present invention. 
         FIG. 26  is a flow chart for illustrating a schematic operation of the image pickup system according to the second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A photographing lens and an image pickup apparatus main body have manufacturing variations and the like. It is not easy to generate a highly-accurate point image intensity distribution taking such manufacturing variations and the like into consideration. 
     Now, embodiments of the present invention are described in detail with reference to the drawings. 
     [First Embodiment] 
     An image pickup apparatus according to a first embodiment of the present invention is described with reference to the drawings. 
     [Configuration of Image Pickup Apparatus] 
     First, the configuration of the image pickup apparatus according to this embodiment is described.  FIG. 1  is a block diagram for illustrating the schematic configuration of the image pickup apparatus according to this embodiment. 
     Note that, a case where an image pickup apparatus is a lens-interchangeable type digital single-lens reflex camera is described herein as an example, but the present invention is not limited thereto. 
     An image pickup apparatus (camera)  10  according to this embodiment includes a lens unit  100  and an image pickup apparatus main body (camera main body, body)  120 . The lens unit  100  is connected to the image pickup apparatus main body (camera main body)  120  via a mount M indicated by the dotted lines at a center portion of  FIG. 1 . 
     The lens unit  100  includes a photographing lens  105  and a lens driving/controlling system  119 . 
     The photographing lens  105  is configured to form an optical image of an object, that is, an object image. The photographing lens  105  includes a first lens group  101 , a diaphragm shutter  102 , a second lens group  103 , and a focus lens group (hereinafter referred to as “focus lens”)  104 . The first lens group  101 , the diaphragm shutter  102 , the second lens group  103 , and the focus lens  104  construct an imaging optical system (photographing optical system, image pickup optical system)  133  configured to form an image of an object on an image pickup element  122 . 
     The lens driving/controlling system  119  is configured to drive or control the lens unit  100 . The lens driving/controlling system  119  includes a zoom actuator  111 , a diaphragm shutter actuator  112 , a focus actuator  113 , a zoom driving circuit  114 , a diaphragm shutter driving circuit  115 , a focus driving circuit  116 , and a lens microprocessor unit (MPU)  117 . The lens driving/controlling system  119  further includes a lens memory  118 . 
     The first lens group  101  is arranged at a leading end portion of the lens unit  100 , and is held to be advanceable and retreatable in an optical axis direction OA. The diaphragm shutter  102  is configured to adjust its aperture diameter to adjust a light amount during photographing. Further, the diaphragm shutter  102  also has a function as an exposure-time adjusting shutter at the time of taking a still image. The diaphragm shutter  102  and the second lens group  103  are integrally operated in an advancing or retreating manner in the optical axis direction OA. Interlocking of the advancing/retreating operation of the second lens group  103  and the advancing/retreating operation of the first lens group  101  realizes a zoom function. Further, the focus lens  104  is advanced or retreated in the optical axis direction OA for focusing. 
     The zoom driving circuit  114  is configured to drive the zoom actuator  111  based on a zoom operation performed by a photographer to operate the first lens group  101  and the second lens group  103  in an advancing or retreating manner in the optical axis direction OA, to thereby perform the zoom operation. The diaphragm shutter driving circuit  115  is configured to drive the diaphragm shutter actuator  112  to control the aperture diameter of the diaphragm shutter  102 , to thereby adjust the light amount during photographing. Further, the diaphragm shutter driving circuit  115  also controls exposure time at the time of taking a still image. The focus driving circuit  116  is configured to drive the focus actuator  113  based on the focus detection result to operate the focus lens  104  in an advancing or retreating manner in the optical axis direction OA for focusing. Further, the focus actuator  113  also has a function as a lens position detecting portion configured to detect the current position of the focus lens  104 . 
     The lens MPU  117  is configured to perform various computing processing for the lens unit  100 , to thereby control the entire lens unit  100 . The lens MPU  117  controls the zoom driving circuit  114 , the diaphragm shutter driving circuit  115 , the focus driving circuit  116 , and the lens memory  118 . Further, the lens MPU  117  is configured to detect the current lens position to notify a camera MPU  125  to be described later of lens position information based on a request from the camera MPU  125 . The lens position information includes information such as the position of the focus lens  104  on the optical axis, the diameter and the position on the optical axis of an exit pupil of the imaging optical system  133 , and the diameter and the position on the optical axis of a lens frame (not shown) for limiting the light fluxes of the exit pupil. The lens memory  118  is configured to store optical information required for automatic focusing (auto-focus), lens light field data to be described later, and other information. 
     On the other hand, the image pickup apparatus main body  120  includes an optical low pass filter (LPF)  121 , the image pickup element  122 , and an image pickup apparatus controlling/driving system (camera controlling/driving system)  131 . 
     The image pickup apparatus controlling/driving system  131  includes an image pickup element driving circuit  123 , an image processing circuit  124 , the camera MPU  125 , a display device  126 , an operation switch group  127 , a memory  128 , an image pickup surface phase-difference focus detection portion  129 , and a TVAF focus detection portion  130 . 
     The optical LPF  121  is configured to reduce the false color and moire of the photographed image. 
     The image pickup element  122  is, for example, a CMOS image sensor. As described later, the image pickup element  122  can output a signal for performing phase-difference focus detection (image pickup surface phase-difference AF). Among pieces of image data acquired by the image pickup element  122 , image data that may be used for the image pickup surface phase-difference AF is converted into focus detection image data (focus detection signal) by the image processing circuit  124 , which is then input to the camera MPU  125 . On the other hand, among the pieces of image data acquired by the image pickup element  122 , image data that may be used for display, recording, or contrast focus detection is subjected to predetermined processing by the image processing circuit  124  depending on the purpose, which is then input to the camera MPU  125 . 
     The image pickup element driving circuit  123  is configured to control the operation of the image pickup element  122 . The image pickup element driving circuit  123  is configured to subject the image signal acquired by the image pickup element  122  to A/D conversion, which is then output to the camera MPU  125  and the image processing circuit  124 . The image processing circuit  124  is configured to subject the image data acquired by the image pickup element  122  to γ conversion, color interpolation, JPEG compression, and other processing. 
     The camera MPU (image pickup apparatus MPU)  125  is configured to perform various computing processing for the image pickup apparatus main body  120 , to thereby control the entire image pickup apparatus main body  120 . The camera MPU  125  is configured to control the image pickup element driving circuit  123 , the image processing circuit  124 , the display device  126 , the operation switch group  127 , the memory  128 , the image pickup surface phase-difference focus detection portion  129 , and the TVAF focus detection portion  130 . Further, the camera MPU  125  is connected to the lens MPU  117  via a signal line of the mount M. The camera MPU  125  is configured to output, to the lens MPU  117 , a lens position information acquiring request for requesting acquisition of the lens position information, or a lens driving request for requesting drive of the lens at a predetermined driving amount. Further, the camera MPU  125  is configured to acquire optical information specific to the lens unit  100 . 
     The camera MPU  125  incorporates a ROM  125   a  having stored thereon a program for controlling the operation of the image pickup apparatus, a RAM  125   b  configured to store variables, and an EEPROM  125   c  configured to store sensor light-receiving intensity characteristics and various parameters. 
     The camera MPU  125  is configured to perform computation for generating a point image intensity distribution to be described later based on the lens light field data to be described later and the sensor light-receiving intensity characteristic to be described later. 
     Note that, as described above, in this embodiment, the lens light field data is stored in, for example, the lens memory  118 , and the sensor light-receiving intensity characteristic is stored in, for example, the EEPROM  125   c . The lens memory  118  functions as a storage portion on the lens unit  100  side (imaging optical system side), and the EEPROM  125   c  functions as a storage portion on the image pickup apparatus main body  120  side. 
     The display device  126  includes an LCD and the like. The display device  126  is configured to display information relating to a photographing mode of the image pickup apparatus, a preview image prior to photographing, a confirming image after photographing, a display image in an in-focus state at the time of focus detection, and the like. The operation switch group  127  includes a power supply switch, a release (photographing trigger) switch, a zoom operation switch, a photographing mode selecting switch, and the like. The memory  128  is, for example, a removable memory such as a flash memory. The memory  128  is configured to record a photographed image. 
     The image pickup surface phase-difference focus detection portion  129  is configured to perform phase-difference focus detection (image pickup surface phase-difference AF) based on the focus detection image data (focus detection signal) obtained through the image processing by the image processing circuit  124 . That is, the image pickup surface phase-difference focus detection portion  129  performs the image pickup surface phase-difference AF based on a shift amount of a pair of images formed on divided pixels  201  and  202  (see  FIG. 2 ) by light fluxes passing through a pair of pupil regions of the photographing optical system  133 . Note that, the image pickup surface phase-difference AF is described in detail later. 
     The TVAF focus detection portion  130  is configured to calculate a TVAF evaluation value based on a contrast component of the image information obtained through the image processing by the image processing circuit  124 , to thereby perform contrast focus detection processing (TVAF). In the contrast focus detection processing, the TVAF evaluation value is calculated at a plurality of focus lens positions while moving the focus lens  104 , to thereby detect the focus lens position having the maximum TVAF evaluation value. The TVAF evaluation value is increased as the image comes into focus, and is the maximum at a focal point. 
     [Image Pickup Element] 
     Next, the image pickup element to be used in the image pickup apparatus according to this embodiment is described.  FIG. 2  is a plan view for illustrating a part of the image pickup element to be used in the image pickup apparatus according to this embodiment. 
     The image pickup element  122  to be used in this embodiment is, as described above, a CMOS image sensor, for example. In a pixel array region (not shown) of the image pickup element  122 , image pickup pixels (pixels)  200  (see  FIG. 2 ) are two-dimensionally arranged, that is, arranged in matrix. Around the pixel array region, peripheral circuits (not shown) including a read-out circuit are arranged. In  FIG. 2 , reference symbol  200 R is used to represent an image pickup pixel responding to red color (R), reference symbol  200 G is used to represent an image pickup pixel responding to green color (G), and reference symbol  200 B is used to represent an image pickup pixel responding to blue color (B). Reference symbol  200  is used to describe the image pickup pixel unless otherwise required to particularly distinguish the responding colors. 
     Each of the image pickup pixels  200  includes two divided pixels (divided regions)  201  and  202 . That is, each of the image pickup pixels  200  includes a first divided pixel  201  and a second divided pixel  202  arranged in 2 columns and 1 row. The center of gravity of the first divided pixel  201  is decentered in a −X direction in the image pickup pixel  200 . The center of gravity of the second divided pixel  202  is decentered in a +X direction in the image pickup pixel  200 . 
     In  FIG. 2 , the arrangement of the image pickup pixels  200  of 4 columns and 4 rows is extracted and illustrated. One image pickup pixel  200  includes two divided pixels  201  and  202 , and hence, in  FIG. 2 , the arrangement of the divided pixels  201  and  202  of 8 columns and 4 rows is extracted and illustrated. 
     The image pickup pixels  200  of 2 columns and 2 rows form one pixel group  203 . In  FIG. 2 , each of the pixel groups  203  is represented with use of the thick solid lines. One pixel group  203  includes one image pickup pixel  200 R responding to red color, two image pickup pixels  200 G responding to green color, and one image pickup pixel  200 B responding to blue color. The image pickup pixel  200 R responding to red color is arranged at an upper left position of the pixel group  203 . The image pickup pixels  200 G responding to green color are arranged at upper right and lower left positions of the pixel group  203 . The image pickup pixel  200 B responding to blue color is arranged at a lower right position of the pixel group  203 . Such a pixel arrangement is called a Bayer pattern. 
     A large number of the pixel groups  203  as described above are arranged two-dimensionally on an image pickup surface (light receiving surface) of the image pickup element  122 , and hence the image pickup element  122  can acquire a clear and highly-accurate photographed image. 
     A pitch (cycle) P of the image pickup pixels  200  is set to, for example, 4 μm. The number of the image pickup pixels  200  arranged in a row direction (X axis direction) is set to, for example, 5,575, and the number of the image pickup pixels  200  arranged in a column direction (Y axis direction) is set to, for example, 3,725. That is, the number N of pixels (effective pixel number) of the image pickup element  122  is set to, for example, about 20,750,000 pixels. Note that, the horizontal direction (row direction, lateral direction) of the image pickup element  122  (right-left direction of the drawing sheet of  FIG. 2 ) is represented by an X axis direction, and the perpendicular direction (column direction, vertical direction) of the image pickup element  122  (up-down direction of the drawing sheet of  FIG. 2 ) is represented by a Y axis direction. Further, a direction normal to the image pickup surface of the image pickup element  122  (direction normal to the drawing sheet of  FIG. 2 ) is represented by a Z axis direction. 
     As described above, each of the image pickup pixels  200  includes the first divided pixel  201  and the second divided pixel  202  arranged in 2 columns and 1 row. Therefore, a pitch (cycle) P AF  of the divided pixels  201  and  202  in the row direction (X axis direction) is, for example, 2 μm. The number of the divided pixels  201  and  202  in the row direction (X axis direction) is, for example, 11,150. The number of the divided pixels  201  and  202  in the column direction (Y axis direction) is, for example, 3,725. The number N AF  of the divided pixels of the image pickup element  122  is, for example, about 41,500,000 pixels. 
       FIG. 3A  and  FIG. 3B  are respectively a plan view and a sectional view for illustrating a pixel portion of the image pickup element.  FIG. 3A  is a plan view for illustrating the pixel portion of the image pickup element, and  FIG. 3B  is a sectional view taken along the line  3 B- 3 B of  FIG. 3A . In  FIG. 3B , an optical axis  303  is represented by using the dashed-dotted line, and a light receiving surface (image pickup surface)  304  of the image pickup element  122  is represented by using the broken line. In  FIG. 3A  and  FIG. 3B , one of the plurality of pixels (image pickup pixels, pixel portions)  200  of the image pickup element is extracted and illustrated. 
     As illustrated in  FIG. 3A  and  FIG. 3B , each of the image pickup pixels  200  is divided into a plurality of regions (divided pixels)  201  and  202 . Specifically, the image pickup pixel  200  is divided into two regions in the X direction, but is not divided in the Y direction. As described above, in this embodiment, each of the image pickup pixels  200  is divided into the two regions  201  and  202 . 
     In one divided pixel  201 , a photoelectric converter (first photoelectric converter)  301  of the first divided pixel  201  is formed in a substrate  300 . In the other divided pixel  202 , a photoelectric converter (second photoelectric converter)  302  of the second divided pixel  202  is formed in the substrate  300 . The center of gravity of the first photoelectric converter  301  is decentered in the −X direction. The center of gravity of the second photoelectric converter  302  is decentered in the +X direction. 
     Examples of the photoelectric converters  301  and  302  include a p-i-n structure photodiode in which an intrinsic layer is sandwiched between a p-type layer and an n-type layer. 
     Note that, each of the photoelectric converters  301  and  302  is not limited to a p-i-n structure photodiode, and may be a p-n junction photodiode in which the intrinsic layer is omitted. 
     On the substrate  300  having the photoelectric converters  301  and  302  formed therein, an insulating layer  311 , a wiring layer  307 , and the like are formed as appropriate. On the substrate  300  having the insulating layer  311 , the wiring layer  307 , and the like formed thereon, a color filter  306  is formed. 
     Note that, the spectral transmittance of the color filter  306  may be varied for each of the image pickup pixels  200 R,  200 G, and  200 B, or the color filter  306  may be omitted as appropriate. 
     On the substrate  300  having the color filter  306  formed thereon, a microlens  305  is arranged, which is configured to collect light entering each of the image pickup pixels  200 . 
     The light entering each of the pixels  200  is collected by the microlens  305  to be dispersed by the color filter  306 , and then reaches the first photoelectric converter  301  and the second photoelectric converter  302 . 
     In the photoelectric converters  301  and  302 , electrons and holes are pair-produced based on the light receiving amount. The pair-produced electrons and holes are separated at a depletion layer. The electrons being negative charges are accumulated in n-type layers  309  and  310 , and the holes being positive charges are discharged outside of the image pickup element  122  through p-type layers connected to a constant voltage source (not shown). 
     The electrons accumulated in the respective n-type layers  309  and  310  of the photoelectric converters  301  and  302  are transferred to a capacitance portion (FD) (not shown) via a transfer gate (not shown), to thereby be converted into voltage signals. 
       FIG. 4  is a schematic diagram for illustrating a correspondence relationship between the pupil region and the pixel portion. The diagram in the lower part of  FIG. 4  is a sectional view of the pixel portion, and the diagram in the upper part of  FIG. 4  is a plan view of an exit pupil plane as viewed from the pixel portion side. 
     As illustrated in  FIG. 4 , a pupil region (exit pupil)  500  includes a first pupil partial region  501  and a second pupil partial region  502 . 
     The center of gravity of the first pupil partial region  501  is decentered in the +X direction in the pupil region  500 . On the other hand, as described above, the center of gravity of the first divided pixel  201  is decentered in the −X direction in the image pickup pixel  200 . Further, the microlens  305  is present between the pupil region  500  and the pixel portion  200 . Therefore, the first pupil partial region  501  and the first divided pixel  201  have a conjugate relationship, and the light flux passing through the first pupil partial region  501  is received in the first divided pixel  201 . 
     The center of gravity of the second pupil partial region  502  is decentered in the −X direction in the pupil region  500 . On the other hand, as described above, the center of gravity of the second divided pixel  202  is decentered in the +X direction in the image pickup pixel  200 . Further, the microlens  305  is present between the pupil region  500  and the pixel portion  200 . Therefore, the second pupil partial region  502  and the second divided pixel  202  have a conjugate relationship, and the light flux passing through the second pupil partial region  502  is received in the second divided pixel  202 . 
     As described above, the pupil region  500  includes the first pupil partial region  501  and the second pupil partial region  502 . Further, as described above, the image pickup pixel  200  includes the first divided pixel  201  and the second divided pixel  202 . Therefore, the light fluxes passing through the pupil region  500  including the first pupil partial region  501  and the second pupil partial region  502  are received by the image pickup pixel  200  including the first divided pixel  201  and the second divided pixel  202 . 
       FIG. 5  is a schematic diagram for illustrating a relationship between the exit pupil and the image pickup element. 
     A plurality of light fluxes emitted from a certain point  801   a  respectively pass through the different pupil partial regions  501  and  502  to be received by a first divided pixel  301   a  and a second divided pixel  302   a  of a certain pixel  200   a , respectively. 
     Further, a plurality of light fluxes emitted from another point  801   b  respectively pass through the different pupil partial regions  501  and  502  to be received by a first divided pixel  301   b  and a second divided pixel  302   b  of another pixel  200   b , respectively. 
     Note that, description is made herein of a case where the pupil region  500  is divided into two regions in the horizontal direction (X direction) as an example, but the present invention is not limited thereto. As necessary, the pupil region  500  may be divided in the perpendicular direction (Y direction). 
     Further, description is made herein of a case where the image pickup pixel  200  includes the first divided pixel  201  and the second divided pixel  202  as an example, but a first focus detection pixel and a second focus detection pixel may be arranged as appropriate separately from the image pickup pixel  200 . 
     A first focus detection signal (first focus detection image data) is formed of an aggregate of signals (light receiving signals) detected by the respective first divided pixels  201  of the image pickup pixels  200  arranged in matrix in the image pickup element  122 . Further, a second focus detection signal (second focus detection image data) is formed of an aggregate of signals (light receiving signals) detected by the respective second divided pixels  202  of the image pickup pixels  200  arranged in matrix in the image pickup element  122 . The thus obtained first focus detection signal and second focus detection signal are used for focus detection. Further, an image pickup signal of the effective pixel number N (image pickup image) is formed of an aggregate of signals obtained by adding signals detected by the respective first divided pixels  201  and signals detected by the respective second divided pixels  202 . 
     [Overview of Auto-Focus Operation] 
     Next, an overview of processing of an auto-focus operation of the image pickup apparatus according to this embodiment is described with reference to  FIG. 6 .  FIG. 6  is a flow chart for illustrating the overview of the processing of the auto-focus operation of the image pickup apparatus according to this embodiment. 
     First, as illustrated in  FIG. 6 , focus detection processing is performed (Step S 601 ). In the focus detection processing, the defocus amount is calculated as described later with reference to  FIG. 7 . 
     Next, point image intensity distribution generation processing is performed (Step S 602 ). Specifically, point image intensity distributions of a plurality of positions in the vicinity of the defocus amount calculated in Step S 601  are generated. The point image intensity distribution generation processing is performed by the camera MPU  125  that may function as a point image intensity distribution generating unit (point image intensity distribution generating portion). In this embodiment, the point image intensity distributions are generated as described above to enable highly-accurate correction of the defocus amount calculated in the focus detection processing (Step S 601 ) and eventually enable setting of a best image plane position. 
     Next, defocus amount correction processing is performed (Step S 603 ). Specifically, a correction value is calculated with use of the point image intensity distributions of the respective plurality of defocus amounts, which are obtained in the point image intensity distribution generation processing (Step S 602 ), and the defocus amount calculated in the focus detection processing (Step S 601 ) is corrected with use of the correction value. 
     Next, the photographing lens  105  is driven (Step S 604 ). Specifically, the photographing lens  105  is driven based on the corrected defocus amount obtained in the defocus amount correction processing (Step S 603 ). 
     Next, in-focus determination processing is performed (Step S 605 ). When it is determined to be in-focus (YES in Step S 605 ), the auto-focus operation is ended. 
     On the other hand, when it is determined to be out-of-focus (NO in Step S 605 ), the processing returns to Step S 601  to perform the processing of the auto-focus operation again. 
     The auto-focus operation of the image pickup apparatus according to this embodiment, which is illustrated in  FIG. 6  as an overview, is described in detail below. 
     [Focus Detection] 
     The focus detection processing (Step S 601 ) schematically described with reference to  FIG. 6  is described in detail below, but prior to the specific description of the focus detection processing, the relationship between the defocus amount and the image shift amount is described with reference to  FIG. 8 . 
       FIG. 8  is a diagram for illustrating the relationship between the defocus amount and the image shift amount. Note that, the above-mentioned image pickup element  122  is arranged at an image pickup surface  800 , but the illustration thereof is omitted in  FIG. 8 . As described above with reference to  FIG. 4  and  FIG. 5 , the exit pupil  500  of the imaging optical system is divided into two regions, that is, the first pupil partial region  501  and the second pupil partial region  502 . 
     Symbol d in  FIG. 8  represents a distance between an imaging position (imaging point) of the object and the image pickup surface, that is, a defocus amount. The magnitude of the defocus amount d is represented by |d|. Under a state in which the imaging position of the object is located on the front side of the image pickup surface, that is, in a front focus state, the sign of the defocus amount is negative (d&lt;0). Under a state in which the imaging position of the object is located on the rear side of the image pickup surface, that is, in a rear focus state, the sign of the defocus amount is positive (d&gt;0). Under a state in which the imaging position of the object is located at the image pickup surface, that is, in an in-focus state, the defocus amount d is 0. 
     When an object  801  is positioned as illustrated in  FIG. 8 , the in-focus state (d=0) is obtained. Further, when an object  802  is positioned as illustrated in  FIG. 8 , the front focus state (d&lt;0) is obtained. Both of the front focus state (d&lt;0) and the rear focus state (d&gt;0) correspond to a defocus state (|d|&gt;0). 
     In the front focus state (d&lt;0), among the light fluxes from the object  802 , the light fluxes passing through the first pupil partial region  501  are collected on the front side of the image pickup surface  800 , and then are spread with a width Γ 1  having a gravity-center position G 1  of the light fluxes as the center, to thereby form a blurred image on the image pickup surface  800 . The blurred image reaching the image pickup surface  800  is received by the first divided pixel  201  of the image pickup pixel  200  arranged in the image pickup element  122 , to thereby generate the first focus detection signal. In this manner, the image of the object  802  with the blur width of Γ 1  is detected as the first focus detection signal at the gravity-center position G 1  on the image pickup surface  800 . 
     Further, in the front focus state (d&lt;0), among the light fluxes from the object  802 , the light fluxes passing through the second pupil partial region  502  are collected on the front side of the image pickup surface  800 , and then are spread with a width Γ 2  having a gravity-center position G 2  of the light fluxes as the center, to thereby form a blurred image on the image pickup surface  800 . The blurred image reaching the image pickup surface  800  is received by the second divided pixel  202  of the image pickup pixel  200  arranged in the image pickup element  122 , to thereby generate the second focus detection signal. In this manner, the image of the object  802  with the blur width of Γ 2  is detected as the second focus detection signal at the gravity-center position G 2  on the image pickup surface  800 . 
     The blur widths Γ 1  and Γ 2  of the object image are increased substantially in proportion to the increase of the magnitude |d| of the defocus amount d. Further, a magnitude |p| of an image shift amount p between the object image represented by the first focus detection signal and the object image represented by the second focus detection signal (difference between the gravity-center positions of the light fluxes (G 1 −G 2 )) is also increased substantially in proportion to the increase of the magnitude |d| of the defocus amount d. 
     The case of the rear focus state (d&gt;0) is similar to the case of the front focus state except that the direction of the image shift between the object image represented by the first focus detection signal and the object image represented by the second focus detection signal is opposite to the direction of the case of the front focus state. 
     The defocus amount and the image shift amount have the above-mentioned relationship therebetween. That is, as the magnitude of the defocus amount d is increased, the magnitude of the image shift amount p between the object image represented by the first focus detection signal and the object image represented by the second focus detection signal is increased. Such a relationship is satisfied, and hence the defocus amount d can be calculated based on the image shift amount p, that is, the phase difference. The focus detection in which the defocus amount is detected based on the phase difference (image shift amount) is referred to as phase-difference focus detection. 
     In the phase-difference focus detection, the first focus detection signal and the second focus detection signal are shifted relatively to each other to calculate a correlation amount representing the degree of matching of those focus detection signals, to thereby detect the image shift amount p based on the shift amount when a satisfactory correlation (degree of matching of the signals) is obtained. As the magnitude of the defocus amount d is increased, the magnitude of the image shift amount p between the object image represented by the first focus detection signal and the object image represented by the second focus detection signal is increased, and hence the image shift amount p can be converted into the defocus amount d. The defocus amount calculated based on the image shift amount p is referred to as detected defocus amount (calculated defocus amount). The detected defocus amount does not always completely match with the actual defocus amount (real defocus amount). Therefore, in this embodiment, the calculated defocus amount (Step S 706 ) is subjected to correction processing (Step S 2105 ) as described later. 
       FIG. 7  is a flow chart for illustrating the focus detection processing in the image pickup apparatus according to this embodiment.  FIG. 7  is a flow chart for describing details of the focus detection processing (Step S 601 ) schematically described with reference to  FIG. 6 . 
     The focus detection processing illustrated in  FIG. 7  is executed by the image pickup element  122 , the image processing circuit  124 , the camera MPU  125 , and the image pickup surface phase-difference focus detection portion  129  in cooperation with each other. Those components function as a focus detection signal generating unit (focus detection signal generating portion) and a focus detection unit (focus detection portion). 
     First, a region on the image pickup element  122  corresponding to the position of the object (object to be focused) is set as a focus detection region (not shown) (Step S 701 ). 
     Next, the focus detection signal generating unit acquires the first focus detection signal generated from the light receiving signals of the first divided pixels  201  in the focus detection region and the second focus detection signal generated from the light receiving signals of the second divided pixels  202  in the focus detection region (Step S 702 ). 
     Next, each of the first focus detection signal and the second focus detection signal is subjected to shading correction processing (optical correction processing) (Step S 703 ). 
     Now, the shading is described with reference to  FIG. 9A  to  FIG. 9C .  FIG. 9A  to  FIG. 9C  are schematic views for describing the shading. 
       FIG. 9A  is an illustration of a case where an exit pupil distance D 1  of the imaging optical system  133  is equal to an exit pupil distance Ds defined on the image pickup element side. In this case, at both of a center image height and a peripheral image height, light fluxes passing through an exit pupil  400  of the imaging optical system  133  are divided substantially equally by the first pupil partial region  501  and the second pupil partial region  502 . 
       FIG. 9B  is an illustration of a case where the exit pupil distance D 1  of the imaging optical system  133  is shorter than the exit pupil distance Ds defined on the image pickup element side. In this case, at the peripheral image height, pupil shift occurs between the exit pupil of the imaging optical system  133  and the entrance pupil of the image pickup element  122 . Therefore, the light fluxes passing through the exit pupil  400  of the imaging optical system  133  are unevenly divided by the first pupil partial region  501  and the second pupil partial region  502 . That is, as illustrated in  FIG. 9B , when the exit pupil distance D 1  of the imaging optical system  133  is shorter than the exit pupil distance Ds defined on the image pickup element side, the pupil division is uneven at the peripheral image height. 
       FIG. 9C  is an illustration of a case where the exit pupil distance D 1  of the imaging optical system  133  is longer than the exit pupil distance Ds defined on the image pickup element side. Also in this case, at the peripheral image height, pupil shift occurs between the exit pupil of the imaging optical system  133  and the entrance pupil of the image pickup element  122 . Therefore, the light fluxes passing through the exit pupil  400  of the imaging optical system  133  are unevenly divided by the first pupil partial region  501  and the second pupil partial region  502 . That is, as illustrated in  FIG. 9C , also when the exit pupil distance D 1  of the imaging optical system  133  is longer than the exit pupil distance Ds defined on the image pickup element side, the pupil division is uneven at the peripheral image height. 
     When the pupil division is uneven at the peripheral image height, the intensities of the first focus detection signal and the second focus detection signal also become uneven. That is, the intensity of one of the first focus detection signal and the second focus detection signal is increased, while the intensity of the other is decreased. Such a phenomenon is called shading. 
     In the phase-difference focus detection, based on the correlation between the first focus detection signal and the second focus detection signal (degree of matching of the signals), the detected defocus amount (in-focus position) is calculated. When the shading occurs due to the pupil shift, there is a case where the correlation between the first focus detection signal and the second focus detection signal (degree of matching of the signals) is reduced. Therefore, in the phase-difference focus detection, in order to improve the correlation between the first focus detection signal and the second focus detection signal (degree of matching of the signals) and enhance the focus detection accuracy, shading correction processing (optical correction processing) is desired to be performed. 
     The shading correction processing is performed as follows. 
     First, based on the image height of the focus detection region and the F value and the exit pupil distance of the photographing lens (imaging optical system), a first shading correction coefficient for correcting the first focus detection signal and a second shading correction coefficient for correcting the second focus detection signal are generated. 
     Then, the first focus detection signal is multiplied by the first shading correction coefficient, and the second focus detection signal is multiplied by the second shading correction coefficient. 
     In this way, the first focus detection signal and the second focus detection signal are subjected to shading correction processing (optical correction processing) (Step S 703 ). 
     Next, the first focus detection signal and the second focus detection signal are subjected to filtering (Step S 704 ).  FIG. 10  is a graph for showing an example of frequency characteristics of a filter to be used in the filtering. The solid line in  FIG. 10  represents an example of the frequency characteristics of the filter. The dashed-dotted line in  FIG. 10  represents another example of the frequency characteristics of the filter. The lateral axis represents spatial frequency, and the vertical axis represents a filter coefficient. 
     When it is presumed that the focus detection is performed under a state in which the defocus amount is large, the filtering may be performed with use of a filter having a low frequency band in a passband. Therefore, in this case, the filter having the frequency characteristics as represented by the solid line in  FIG. 10  can be used. 
     On the other hand, when the focus detection is enabled not only under a state in which the defocus amount is large but also under a state in which the defocus amount is small, it is preferred to use a filter having even a high frequency band in the passband. In this case, the filter having the frequency characteristics as represented by the dashed-dotted line in  FIG. 10 , that is, a filter having not only the low frequency band but also the high frequency band in the passband is preferred to be used. 
     In this way, the first focus detection signal and the second focus detection signal are subjected to filtering (Step S 704 ). 
     Next, shifting is performed, which is processing of shifting the first focus detection signal and the second focus detection signal relatively in a pupil division direction, to thereby calculate the correlation amount representing the degree of matching of those signals (Step S 705 ). Such shifting is performed with use of the first focus detection signal subjected to filtering and the second focus detection signal subjected to filtering. 
     When s 1  represents the shift amount by the shifting and Γ 1  represents a shift range of the shift amount s 1 , a correlation amount COR representing the degree of matching between the first focus detection signal and the second focus detection signal is calculated by the following expression (1). In this case, A(k) represents the k-th signal in the first focus detection signal, and B(k) represents the k-th signal in the second focus detection signal. Symbol W represents the range of the number k corresponding to the focus detection region. 
     
       
         
           
             
               
                 
                   
                     
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     When the correlation amount COR is calculated, a second focus detection signal B(k−s 1 ) that is the (k−s 1 )th signal is subtracted from a first focus detection signal A(k) that is the k-th signal, to thereby generate a shift subtracting signal and obtain the absolute value of the shift subtracting signal. The value of the number k is sequentially changed within the range W corresponding to the focus detection region, and the sum of the absolute values of the shift subtracting signals is obtained, to thereby calculate a correlation amount COR(s 1 ). As necessary, the correlation amount (evaluation value) calculated for each row may be added for a plurality of rows for each shift amount. 
     In this manner, the correlation amount representing the degree of matching between the first focus detection signal and the second focus detection signal is calculated for each shift amount s 1  (Step S 705 ). 
     Next, defocus amount calculation processing is performed (Step S 706 ). In the defocus amount calculation processing, first, based on the shift amount s 1  obtained when the correlation amount takes the minimum value, an image shift amount p 1  is calculated. Then, the calculated image shift amount p 1  is multiplied by the image height of the focus detection region, the F value of the photographing lens (imaging optical system)  105  and a conversion coefficient K corresponding to the exit pupil distance, to thereby calculate the defocus amount (detected defocus amount). 
     In this manner, the defocus amount is calculated by the phase-difference focus detection. As described above, the thus calculated defocus amount does not always completely match with the actual defocus amount (real defocus amount). Therefore, in this embodiment, as described later, the defocus amount calculated in the defocus amount calculation processing (Step S 706 ) is subjected to correction processing (Step S 2105 ). 
     [Point Image Intensity Distribution] 
     Generation of the point image intensity distribution schematically described with reference to  FIG. 6  (Step S 602 ) is described in detail below, but prior to the specific description of the generation of the point image intensity distribution, the point image intensity distribution is described below. 
       FIG. 11A  to  FIG. 11C  are diagrams for describing the point image intensity distribution.  FIG. 11A  is a diagram for describing the difference in point image intensity distribution due to the difference in defocus amount, and for describing the difference in point image intensity distribution due to the difference in image height.  FIG. 11B  is a diagram for describing the difference in point image intensity distribution due to the difference in aperture value.  FIG. 11C  is a diagram for describing the difference in point image intensity distribution due to presence or absence of lens aberration. 
       FIG. 12A  to  FIG. 12E  are diagrams for illustrating the point image intensity distributions. The lateral axis of  FIG. 12A  to  FIG. 12E  represents a position of the image pickup surface of the image pickup element  122  in the horizontal direction (X direction), and the vertical axis of  FIG. 12A  to  FIG. 12E  represents the light intensity. 
       FIG. 12A  is the point image intensity distribution when light from a point light source  1101  at the center image height reaches the image pickup surface located at a position  1111 .  FIG. 12B  is the point image intensity distribution when the light from the point light source  1101  at the center image height reaches the image pickup surface located at a position  1112 .  FIG. 12C  is the point image intensity distribution when light from a point light source  1102  at a peripheral image height reaches the image pickup surface located at the position  1111 .  FIG. 12D  is the point image intensity distribution when an aperture of a diaphragm  1131   b  is narrowed.  FIG. 12E  is the point image intensity distribution when lens aberration is present. 
     The point image intensity distribution represents a light intensity distribution when the light from the point light source is received on the light receiving surface (image pickup surface) of the image pickup element. As illustrated in  FIG. 12A  to  FIG. 12E , the point image intensity distribution differs depending on the difference in defocus amount, the difference in image height, the difference in aperture value, and the difference in lens aberration. 
     The difference in point image intensity distribution due to the difference in defocus amount can be described with reference to  FIG. 12A  and  FIG. 12B .  FIG. 12A  is an example in which the image pickup surface of the image pickup element  122  is located at the position  1111  at which the light flux from the point light source  1101  is imaged.  FIG. 12B  is an example in which the image pickup surface of the image pickup element  122  is located at the position  1112  on the front side of the position  1111  at which the light flux from the point light source  1101  is imaged. That is,  FIG. 12A  corresponds to a case where the defocus amount is 0, and  FIG. 12B  corresponds to a case where the defocus amount is not 0. As is understood through comparison between  FIG. 12A  and  FIG. 12B , when the defocus amount differs, the spreading of the point image intensity distribution and the peak value of the point image intensity distribution differ. 
     As described above, the point image intensity distribution differs depending on the difference in defocus amount. In this embodiment, as described later, the point image intensity distribution is calculated with use of the lens light field data to be described later, which represents the information of the light flux in a vector form. Therefore, the point image intensity distribution that differs depending on the difference in defocus amount as described above can be calculated. 
     The difference in point image intensity distribution due to the difference in image height can be described with reference to  FIG. 12A  and  FIG. 12C .  FIG. 12A  is an example of the case where the light flux from the point light source  1101  at the center image height is imaged on the image pickup surface of the image pickup element  122  located at the position  1111 .  FIG. 12C  is an example of the case where the light flux from the point light source  1102  at the peripheral image height is imaged on the image pickup surface of the image pickup element  122  located at the position  1111 . A light flux  1121   a  from the point light source  1101  at the center image height and a light flux  1122   a  from the point light source  1102  at the peripheral image height differ in incident angle to the photographing lens  105 , and also differ in incident angle to the image pickup surface of the image pickup element  122 . Therefore, as is understood through comparison between  FIG. 12A  and  FIG. 12C , the difference in image height affects the symmetric property of the shape of the point image intensity distribution. That is, in  FIG. 12A , the shape of the point image intensity distribution is bilaterally symmetric, but in  FIG. 12C , the shape of the point image intensity distribution is not bilaterally symmetric and is biased. 
     As described above, the point image intensity distribution differs depending on the difference in image height. Therefore, the lens light field data to be described later is required to be held for each image height. 
     The difference in point image intensity distribution due to the difference in aperture value can be described with reference to  FIG. 12A  and  FIG. 12D .  FIG. 12A  corresponds to  FIG. 11A , and is an example of a case where an aperture of a diaphragm  1131   a  is relatively large.  FIG. 12D  corresponds to  FIG. 11B , and is an example of a case where the aperture of the diaphragm  1131   b  is relatively small. The diaphragm  1131   a  and the diaphragm  1131   b  differ from each other in size of the aperture, and hence the diaphragms  1131   a  and  1131   b  differ from each other in width of the light fluxes passing therethrough. Therefore, there is a difference in range of the light fluxes reaching the image pickup surface of the image pickup element  122 . As is understood through comparison between  FIG. 12A  and  FIG. 12D , the difference in aperture value causes difference in spreading of the point image intensity distribution, and further causes difference in peak value of the point image intensity distribution. Note that, in this case, the influence of diffraction is not taken into consideration. 
     As described above, as the aperture value is reduced, the light flux  1121   a  is vignetted by the diaphragm  1131   b , that is, vignetting occurs. Therefore, the range of the light fluxes reaching the image pickup surface of the image pickup element  122  is limited. Therefore, as described later, based on the vignetting information, part of the lens light field data is selectively used. 
     The difference in point image intensity distribution due to the difference in lens aberration can be described with reference to  FIG. 12A  and  FIG. 12E .  FIG. 12A  corresponds to  FIG. 11A , and is an example of a case where aberration is absent.  FIG. 12E  corresponds to  FIG. 11C , and is an example of a case where aberration is present. The light flux  1121   a  illustrated in  FIG. 11A  and a light flux  1121   c  illustrated in  FIG. 11C  differ from each other in optical path after being refracted by the lens. When aberration is present, as illustrated in  FIG. 11C , the light fluxes do not intersect at one point. As is understood through comparison between  FIG. 12A  and  FIG. 12E , the difference in lens aberration causes the difference in point image intensity distribution. When aberration is present, the light fluxes do not intersect at one point. Therefore, in both cases of front focus and rear focus, the shape is not similar to the shape of the point image intensity distribution illustrated in  FIG. 12A , which may cause offset at the time of focus detection. Note that, the offset is described in detail later. 
     As described above, the point image intensity distribution differs depending on the difference in defocus amount, image height, aperture value, aberration, and the like. 
     [Point Image Intensity Distribution Generation Processing] 
     Next, the point image intensity distribution generation processing is described with reference to  FIG. 13 .  FIG. 13  is a flow chart for illustrating the point image intensity distribution generation processing in the image pickup apparatus according to this embodiment. FIG.  13  is a flow chart for describing details of the point image intensity distribution generation processing (Step S 602 ) schematically described with reference to  FIG. 6 . 
     The point image intensity distribution generation processing illustrated in  FIG. 13  is executed by the ROM  125   a , the lens memory  118 , the camera MPU  125 , and the like in cooperation with each other. The ROM  125   a  functions as a sensor light-receiving intensity characteristic storage unit (sensor light-receiving intensity characteristic storage portion). The lens memory  118  functions as a lens light field data storage unit (lens light field data storage portion). The camera MPU  125  functions as the point image intensity distribution generating unit (point image intensity distribution generating portion). 
     First, a condition when the focus detection processing (Step S 601 ) is performed, that is, a focus detection condition is acquired (Step S 1301 ). The focus detection condition refers to information when the focus detection is performed, such as the image height, the aperture value, the lens zoom state, and the lens focus state. 
     Next, the defocus amount calculated in the defocus amount calculation processing (Step S 706 ) is acquired (Step S 1302 ). 
     Next, the sensor light-receiving intensity characteristic is acquired (Step S 1303 ). The sensor light-receiving intensity characteristic is a characteristic specific to the image pickup element  122 , and hence is stored in advance in the ROM  125   a  serving as the sensor light-receiving intensity characteristic storage unit. The sensor light-receiving intensity characteristic represents the light-receiving intensity of the light flux passing through each region of the entrance pupil of the microlens arranged on the image pickup element on the light receiving surface  304  of the image pickup element  122 . In other words, the sensor light-receiving intensity characteristic represents a light-receiving intensity distribution of the light flux reaching each pixel of the image pickup element  122  on the light receiving surface  304  of the image pickup element  122 . Note that, the sensor light-receiving intensity characteristic is described in detail later. 
     Next, the lens light field data is acquired (Step S 1304 ). The lens light field data is data specific to the lens, and hence is stored in advance in the lens memory  118  serving as the lens light field data storage unit. The lens memory  118  stores various pieces of lens light field data corresponding to the focus detection condition and the defocus amount. Therefore, the lens light field data corresponding to the focus detection condition acquired in Step S 1301  and the defocus amount acquired in Step S 1302  is read out from the lens memory  118 . The lens light field data includes information relating to directions of a plurality of light fluxes emitted from one point of the object position and passing through different regions of the exit pupil of the imaging optical system, and information relating to positions of points on the respective light fluxes. The lens light field data may further include information relating to the intensities of the light fluxes in addition to the information relating to the directions of the light fluxes and the information relating to the positions of the points on the light fluxes. Note that, in this case, the information relating to the intensities of the light fluxes refers to information taking a lens transmittance distribution into consideration. Further, the intensity of the light flux is represented by a length component of a vector. Therefore, the lens light field data including the information relating to the directions of the light fluxes, the positions of the points on the light fluxes, and the intensities of the light fluxes can also be represented by information relating to the starting points and the end points of the light fluxes. Note that, the lens light field data is described in detail later. 
     Next, from the lens light field data read out in Step S 1304 , a region to be used is determined (Step S 1305 ). A lens light field data usage region is determined based on the focus detection condition acquired in Step S 1301 . Specifically, the lens light field data of a part vignetted by a vignetting frame  1505  is not used, and only the lens light field data of a part not vignetted by the vignetting frame  1505  is used. The lens light field data is stored as information of each region of the exit pupil, and hence such selection of only a partial region is possible. Note that, the vignetting frame  1505  is described in detail later. 
     Next, processing of calculating sensor light-receiving light field data is performed (Step S 1306 ). In the sensor light-receiving light field data calculation processing, based on a sensor light-receiving intensity characteristic  1401  acquired in Step S 1303  and the lens light field data whose usage region is determined in Step S 1305 , the sensor light-receiving light field data is calculated. Specifically, the sensor light-receiving light field data is calculated by a product of the intensities of the plurality of light fluxes represented by the lens light field data and the sensor light-receiving intensity characteristic in the region corresponding to the plurality of light fluxes. 
     Next, processing of generating the point image intensity distribution is performed (Step S 1307 ). In the point image intensity distribution generation processing, based on the sensor light-receiving light field data calculated in Step S 1306 , a plurality of point image intensity distributions obtained when the position of the light receiving surface  304  of the image pickup element  122  is varied in the optical axis direction are generated. 
       FIG. 14  is a diagram for illustrating a relationship among the lens light field data, the sensor light-receiving intensity characteristic, and the point image intensity distribution. The X axis in  FIG. 14  represents the horizontal direction of the exit pupil plane, and the Z axis in  FIG. 14  represents the optical axis direction. 
     Reference symbol  1401  represents a distribution obtained when the sensor light-receiving intensity characteristic (sensor light-receiving intensity distribution) is projected on the exit pupil plane. Note that, the sensor light-receiving intensity characteristic represents, as described above, the intensity of each light flux reaching each pixel  200  on the light receiving surface  304  of the image pickup element  122 , and does not represent the intensity of each light flux on the exit pupil plane. In  FIG. 14 , for the sake of easy understanding of the description, the sensor light-receiving intensity characteristic is projected on the exit pupil plane. 
     Reference symbol  1402  represents the lens light field data. Reference symbol  1403  represents the sensor light-receiving light field data. Reference symbols  1404   a ,  1404   b , and  1404   c  represent positions of the image pickup element  122 , that is, sensor positions. Reference symbols  1405   a ,  1405   b , and  1405   c  represent the point image intensity distributions at the respective sensor positions  1404   a ,  1404   b , and  1404   c . Note that, those point image intensity distributions  1405   a ,  1405   b , and  1405   c  are generated based on the sensor light-receiving light field data  1403 . 
     The sensor light-receiving light field data  1403  is obtained by a product of the intensities of the plurality of light fluxes represented by the lens light field data  1402  and the sensor light-receiving intensity characteristic  1401  of the region corresponding to the plurality of light fluxes. At coordinates at which the intensity of the sensor light-receiving intensity characteristic  1401  is large, the sensor light-receiving light field data  1403  is large. 
     The point image intensity distribution  1405   a  is calculated by integrating the light-receiving intensities at the sensor position  1404   a  of the light fluxes in the sensor light-receiving light field data based on the reaching points at the sensor position  1404   a  of the light fluxes in the sensor light-receiving light field data  1403 . The point image intensity distribution  1405   b  is calculated by integrating the light-receiving intensities at the sensor position  1404   b  of the light fluxes in the sensor light-receiving light field data based on the reaching points at the sensor position  1404   b  of the light fluxes in the sensor light-receiving light field data  1403 . The point image intensity distribution  1405   c  is calculated by integrating the light-receiving intensities at the sensor position  1404   c  of the light fluxes in the sensor light-receiving light field data based on the reaching points at the sensor position  1404   c  of the light fluxes in the sensor light-receiving light field data  1403 . At the time of integrating the light-receiving intensities of the light fluxes on the sensor light-receiving light field data  1403 , the integration is performed at intervals (pitches) of the pixels  200  arranged in the image pickup element  122 . 
     As described above, the sensor light-receiving light field data is calculated based on the product of the sensor light-receiving intensity characteristic and the lens light field data, and the point image intensity distributions at a plurality of defocus positions are generated based on the sensor light-receiving light field data. 
     [Sensor Light-Receiving Intensity Characteristic] 
     Next, the sensor light-receiving intensity characteristic is described. 
     Note that, as described above, the sensor light-receiving intensity characteristic is a characteristic specific to the image pickup element  122 , and hence is stored in advance in, for example, the ROM  125   a  serving as the sensor light-receiving intensity characteristic storage unit. 
       FIG. 15A  to  FIG. 15F  are schematic diagrams for illustrating the sensor light-receiving intensity characteristic. In  FIG. 15A  to  FIG. 15F , the sensor light-receiving intensity characteristic is illustrated by being projected on the exit pupil plane. As described above, the sensor light-receiving intensity characteristic represents the intensity of each light flux reaching each pixel  200  on the light receiving surface  304  of the image pickup element  122 , and does not represent the distribution of the intensity of the light flux on the exit pupil plane. In this case, for the sake of easy understanding of the description, the sensor light-receiving intensity characteristic is illustrated by being projected on the exit pupil plane. 
       FIG. 15A  is a two-dimensional illustration of a sensor light-receiving intensity characteristic  1501   a  of the light fluxes passing through the first pupil partial region  501 , and represents a case where vignetting does not occur.  FIG. 15B  is a two-dimensional illustration of a sensor light-receiving intensity characteristic  1501   b  of the light fluxes passing through the second pupil partial region  502 , and represents a case where vignetting does not occur.  FIG. 15C  is a one-dimensional illustration of sensor light-receiving intensity characteristics, and represents a case where vignetting does not occur. Reference symbol  1502   a  represents the sensor light-receiving intensity characteristic of the light fluxes passing through the first pupil partial region  501 , and reference symbol  1502   b  represents the sensor light-receiving intensity characteristic of the light fluxes passing through the second pupil partial region  502 . 
       FIG. 15D  is a two-dimensional illustration of a sensor light-receiving intensity characteristic  1503   a  of the light fluxes passing through the first pupil partial region  501 , and represents a case where vignetting occurs.  FIG. 15E  is a two-dimensional illustration of a sensor light-receiving intensity characteristic  1503   b  of the light fluxes passing through the second pupil partial region  502 , and represents a case where vignetting occurs.  FIG. 15F  is a one-dimensional illustration of sensor light-receiving intensity characteristics, and represents a case where vignetting occurs. 
     The X axis and the Y axis of  FIG. 15A ,  FIG. 15B ,  FIG. 15D , and  FIG. 15E  represent coordinates on the exit pupil plane.  FIG. 15A ,  FIG. 15B ,  FIG. 15D , and  FIG. 15E  represent the intensity of the light by the density of the dots. Denser dots represent higher light intensity, and sparser dots represent lower light intensity. Reference symbol  1505  in  FIG. 15D  and  FIG. 15E  represents the vignetting frame. The vignetting frame refers to a boundary of vignetting by a lens frame and a diaphragm frame, and is held as vignetting information. The X axis of  FIG. 15C  and  FIG. 15F  represents the horizontal direction of the exit pupil plane. 
     When the vignetting does not occur, the sensor light-receiving intensity characteristics illustrated one-dimensionally have distributions as reference symbols  1502   a  and  1502   b  of  FIG. 15C . 
     In contrast, when the vignetting occurs, the sensor light-receiving intensity characteristics illustrated one-dimensionally have distributions as reference symbols  1504   a  and  1504   b  of  FIG. 15F . 
     As described above, the sensor light-receiving intensity characteristic is dependent on the vignetting frame  1505  and the pupil shape. 
     Note that, in this case, the sensor light-receiving intensity characteristic at the center image height is described as an example, but the sensor light-receiving intensity characteristic at the peripheral image height is similar to the above. Note that, at the peripheral image height, the vignetting frame  1505  may not have a circular shape. 
     As described above, the sensor light-receiving intensity characteristic represents the intensity of each light flux reaching each pixel  200  on the light receiving surface  304  of the image pickup element  122 . However, when the lens light field data is defined by the coordinates on the exit pupil plane, it is preferred that the sensor light-receiving intensity characteristic be also defined by the coordinates on the exit pupil plane. This is because, by defining the lens light field data and the sensor light-receiving intensity characteristic by coordinates on the same plane, the calculation of the sensor light-receiving light field data is facilitated. In this case, the lens light field data is defined on the exit pupil plane, and the sensor light-receiving intensity characteristic is also defined by coordinates obtained when the sensor light-receiving intensity characteristic is projected on the exit pupil plane. 
     The sensor light-receiving intensity characteristic is data representing the two-dimensional distribution of the intensity of the light flux reaching each pixel  200  on the light receiving surface  304  of the image pickup element  122 , and is held correspondingly to XY coordinates obtained when the sensor light-receiving intensity characteristic is projected on the exit pupil plane. 
     Note that, the lens light field data may be defined by coordinates on a plane different from the exit pupil plane. In this case, the sensor light-receiving intensity characteristic is held correspondingly to XY coordinates obtained when the sensor light-receiving intensity characteristic is projected on the same plane as the plane on which the lens light field data is defined. 
     The difference in sensor light-receiving intensity characteristic is caused also depending on the difference in type (model, kind) of the image pickup element  122 .  FIG. 16  is a graph for showing the difference in sensor light-receiving intensity characteristic due to the difference in type of the image pickup element. The lateral axis X represents the horizontal direction of the exit pupil plane, and the vertical axis represents the light-receiving intensity. 
     Reference symbol  1601   a  one-dimensionally represents a sensor light-receiving intensity characteristic of a case where the light fluxes passing through the first pupil partial region  501  are received by a first image pickup element (not shown). Reference symbol  1601   b  one-dimensionally represents a sensor light-receiving intensity characteristic of a case where the light fluxes passing through the second pupil partial region  502  are received by the first image pickup element. 
     Reference symbol  1602   a  one-dimensionally represents a sensor light-receiving intensity characteristic of a case where the light fluxes passing through the first pupil partial region  501  are received by a second image pickup element (not shown) of a type different from that of the first image pickup element. Reference symbol  1602   b  one-dimensionally represents a sensor light-receiving intensity characteristic of a case where the light fluxes passing through the second pupil partial region  502  are received by the second image pickup element. 
     The sensor light-receiving intensity characteristic  1601   a  of the first image pickup element is remarkably lower than the sensor light-receiving intensity characteristic  1602   a  of the second image pickup element in a region having a negative X coordinate value. 
     Further, the sensor light-receiving intensity characteristic  1601   b  of the first image pickup element is remarkably lower than the sensor light-receiving intensity characteristic  1602   b  of the second image pickup element in a region having a positive X coordinate value. 
     The difference in sensor light-receiving intensity characteristic is caused depending on the type of the image pickup element because the vignetting due to, for example, a multi-layer wiring structure arranged above the light receiving surface  304  of the image pickup element  122  differs depending on the type of the image pickup element. 
     The difference in sensor light-receiving intensity characteristic is caused also due to, for example, misalignment caused when the image pickup element  122  is mounted to the image pickup apparatus main body  120 . That is, when the image pickup element  122  is mounted to the image pickup apparatus main body  120 , the light receiving surface  304  of the image pickup element  122  may be tilted with respect to the entrance pupil plane. The distance from the light receiving surface  304  of the image pickup element  122  to the exit pupil plane (pupil distance) is several tens of millimeters. Therefore, when the light receiving surface  304  of the image pickup element  122  is tilted by several degrees with respect to the exit pupil plane, the optical axis is misaligned at a level of several millimeters on the exit pupil plane. The pixel pitch of the image pickup element  122  is generally several micrometers, and hence the misalignment of the optical axis at the level of several millimeters cannot be ignored. 
       FIG. 17A  and  FIG. 17B  are schematic diagrams for illustrating influences on the sensor light-receiving intensity characteristic due to the misalignment caused when the image pickup element is mounted.  FIG. 17A  is an example of a case where the image pickup element  122  is normally mounted to the image pickup apparatus main body  120 .  FIG. 17B  is an example of a case where the image pickup element  122  is mounted to the image pickup apparatus main body  120  in a tilted manner. The X axis represents the horizontal direction of the image pickup element  122 , and the Z axis represents the optical axis direction. 
     The diagram in the upper part of  FIG. 17A  and the diagram in the upper part of  FIG. 17B  represent distributions when the sensor light-receiving intensity characteristics are projected on the exit pupil plane. Reference symbols  1701   a  and  1703   a  one-dimensionally represent sensor light-receiving intensity characteristics of the light fluxes passing through the first pupil partial region  501 . Further, reference symbols  1701   b  and  1703   b  one-dimensionally represent sensor light-receiving intensity characteristics of the light fluxes passing through the second pupil partial region  502 . Reference symbol  1702  represents the image pickup element  122  mounted parallel to the exit pupil plane, and reference symbol  1704  represents the image pickup element  122  mounted in a tilted manner with respect to the exit pupil plane. 
     Symbol dx of  FIG. 17B  represents a misalignment amount of the optical axis, which differs depending on the tilting angle of the light receiving surface  304  of the image pickup element  122  with respect to the exit pupil plane. 
     Note that, in this case, the misalignment in the X direction is described as an example, but the same holds true also in the misalignment in the Y direction. 
     As described above, the sensor light-receiving intensity characteristic differs also depending on the difference in type of the image pickup element  122  or misalignment caused when the image pickup element  122  is mounted to the image pickup apparatus main body  120 . In this embodiment, the point image intensity distributions are generated with use of information taking such differences into consideration, and hence satisfactory point image intensity distributions can be generated. Therefore, according to this embodiment, the correction value to be used for correction in defocus amount correction to be described later can be calculated at high accuracy. 
     [Lens Light Field Data] 
     Next, the lens light field data is described in detail. 
     The lens light field data includes information relating to directions of a plurality of light fluxes emitted from one point of the object position and passing through different regions of the exit pupil of the imaging optical system, and information relating to positions of points on the light fluxes. The lens light field data may further include information relating to intensities of the light fluxes in addition to the information relating to the directions of the light fluxes and the information relating to the positions of the points on the light fluxes. 
     The intensity of the light flux may be represented by a length component of a vector, and hence the lens light field data including information relating to the directions of the light fluxes, the positions of the points on the light fluxes, and the intensities of the light fluxes can be also represented by information relating to the starting points and the end points of the light fluxes. 
     The lens light field data may be represented by six-dimensional information at the maximum, which is obtained by adding, for example, three-dimensional information representing the position of the point on the light flux, two-dimensional information representing the direction of the light flux, and one-dimensional information representing the intensity of the light flux. 
     As described above, the lens light field data does not represent information of the light flux by information representing refraction at each lens surface as in a ray tracing diagram, but represents information of the light flux through processing into information representing the direction of the light flux and the position of the point on the light flux. The lens light field data is represented by such information, and hence has a small data amount and is easy to handle when the point image intensity distribution is generated. 
       FIG. 18A  to  FIG. 18C  are schematic diagrams for two-dimensionally illustrating the lens light field data.  FIG. 18A  is the lens light field data at the center image height, and  FIG. 18B  is the lens light field data at the peripheral image height of 80%.  FIG. 18C  is the lens light field data at the peripheral image height of 100%. All of  FIG. 18A  to  FIG. 18C  are the lens light field data associated with the exit pupil plane. Note that, the lens light field data is not limited to be associated with the exit pupil plane, and may be associated with a plane different from the exit pupil plane. 
     As illustrated in  FIG. 18A , in the case of the center image height, the region of the lens light field data is determined based on only the vignetting by the diaphragm  1131   a.    
     On the other hand, as illustrated in  FIG. 18B , at the peripheral image height of 80%, vignetting occurs not only by the diaphragm  1131   a  but also by the lens frame. Therefore, with the vignetting frame obtained by combining the diaphragm  1131   a  and the lens frame, a region that may define the lens light field data is determined. The region that may define the lens light field data in the case of the peripheral image height of 80% is narrower than the region that may define the lens light field data in the case of the center image height. 
     As the image height is increased, the vignetted region is increased. Therefore, in the case of the peripheral image height of 100%, as illustrated in  FIG. 18C , the region that may define the lens light field data is further narrowed. 
     Further, the vignetting frame changes depending on the aperture value, and hence the region of the lens light field data also differs depending on the aperture value. 
     As described above, the region that may define the lens light field data is determined based on the vignetting frame (vignetting information) that differs depending on the aperture value and the image height. Therefore, when the usage region is determined from the lens light field data (Step S 1305  of  FIG. 13 ), the usage region of the lens light field data is determined based on the focus detection condition such as the aperture value and the image height. 
       FIG. 19A  and  FIG. 19B  are schematic diagrams for illustrating a relationship between presence or absence of aberration and collection of light fluxes.  FIG. 19A  is an illustration of a state of the collection of the light fluxes when the aberration is absent, and  FIG. 19B  is an illustration of a state of the collection of the light fluxes when the aberration is present. 
     When the aberration is absent, as illustrated in  FIG. 19A , the light fluxes intersect at one point. 
     On the other hand, when the aberration is present, as illustrated in  FIG. 19B , the light fluxes do not intersect at one point. In the actual imaging optical system  133 , aberration is present, and hence the light fluxes are collected as illustrated in  FIG. 19B , for example. 
     The lens light field data can be expressed in consideration of the influence of aberration in the imaging optical system  133 . The aberration in the imaging optical system  133  differs depending on the type (model) of the imaging optical system (lens)  133 , the manufacturing variations of the imaging optical system  133 , and the like. The influence of the aberration is taken into consideration in the lens light field data, and hence the point image intensity distribution can be generated in consideration of the lens aberration. 
       FIG. 20A  to  FIG. 20C  are schematic diagrams for illustrating a method of forming the lens light field data. 
       FIG. 20A  is a ray tracing diagram of the light fluxes from an object  2001 . The ray tracing diagram of  FIG. 20A  includes information of refraction at each lens surface of each light beam from the object  2001 . 
       FIG. 20B  is an example of the lens light field data. As illustrated in  FIG. 20B , the straight line including the trajectory of the light flux exiting from a rear lens  2002  is extended in a direction opposite to the traveling direction of the light flux, and on the extended line, the information of the coordinates of the starting point, the information of the direction, and the information of the intensity are defined, to thereby obtain the lens light field data. The lens light field data is held in a form of a vector, for example. Reference symbol  2003   a  in  FIG. 20B  represents a vector group forming the lens light field data. 
       FIG. 20C  is an example of the lens light field data in a case where the starting point coordinates are aligned on the exit pupil plane. In  FIG. 20C , the coordinates of the starting points of a vector group  2003   b  forming the lens light field data are set on the exit pupil plane. In the case as in  FIG. 20C , the data amount of the lens light field data can be reduced to three-dimensional information including two-dimensional information relating to the direction of the light flux and one-dimensional information relating to the intensity of the light flux. Further, when the intensity of the light flux is not taken into consideration, the data amount of the lens light field data can be reduced to the two-dimensional information relating to the direction of the light flux. 
     Note that, in  FIG. 20C , the coordinates of the starting points of the vector group forming the lens light field data are aligned on the exit pupil plane, but the coordinates are not limited to be aligned on the exit pupil plane. The coordinates of the starting points of the vectors can be aligned on an arbitrary plane. 
     In this embodiment, positional information defined in advance between the photographing lens  105  and the image pickup apparatus main body  120  is used as information of the positions of the starting points of the vector group  2003   b  forming the lens light field data. Therefore, even when the combination between the photographing lens  105  and the image pickup apparatus main body  120  is changed, the point image intensity distribution can be generated by common processing, thereby being capable of facilitating data processing. 
     The difference in type (model) and the manufacturing variations of the photographing lens  105  cause the difference in direction of the light flux traveling through the photographing lens  105 , for example. In this embodiment, the point image intensity distribution is generated with use of the lens light field data specific to the photographing lens  105  to be used, and hence a satisfactory point image intensity distribution can be generated in consideration of such differences. Therefore, according to this embodiment, the correction value to be used in the defocus amount correction to be described later can be calculated at high accuracy. 
     [Defocus Amount Correction Processing] 
     Next, the defocus amount correction processing is described.  FIG. 21  is a flow chart for illustrating the defocus amount correction processing of the image pickup apparatus according to this embodiment.  FIG. 21  is a flow chart for describing details of the defocus amount correction processing (Step S 603 ) schematically described with reference to  FIG. 6 . 
     The defocus amount correction processing illustrated in  FIG. 21  is executed by the ROM  125   a , the lens memory  118 , the camera MPU  125 , and the like in cooperation with each other. The ROM  125   a  functions as the sensor light-receiving intensity characteristic storage unit (sensor light-receiving intensity characteristic storage portion). The lens memory  118  functions as the lens light field data storage unit (lens light field data storage portion). The camera MPU  125  functions as the point image intensity distribution generating unit (point image intensity distribution generating portion) configured to generate the point image intensity distribution and a correction value calculating unit (correction value calculating portion) configured to calculate the correction value. 
     First, point image intensity distributions of a plurality of defocus positions are acquired (Step S 2101 ). Specifically, for example, the point image intensity distribution of a case where the position of the image pickup element  122  (sensor position) is located at a first position  2404  (see  FIG. 24F ) is acquired. Further, the point image intensity distribution of a case where the position of the image pickup element  122  is located at a second position  2405  (see  FIG. 24F ) is acquired. Further, the point image intensity distribution of a case where the position of the image pickup element  122  is located at a third position  2406  (see  FIG. 24F ) is acquired. 
     When the point image intensity distributions of the respective sensor positions  2404 ,  2405 , and  2406  are acquired, the following point image intensity distributions are acquired. That is, the point image intensity distribution of the light fluxes passing through the first pupil partial region  501  and reaching the first divided pixel  201  is acquired. Further, the point image intensity distribution of the light fluxes passing through the second pupil partial region  502  and reaching the second divided pixel  202  is acquired. Further, the point image intensity distribution of the light fluxes passing through the pupil region  500  including the first pupil partial region  501  and the second pupil partial region  502  and reaching the image pickup pixel  200  including the first divided pixel  201  and the second divided pixel  202  is acquired. 
     The point image intensity distribution of the light fluxes passing through the first pupil partial region  501  and reaching the first divided pixel  201  and the point image intensity distribution of the light fluxes passing through the second pupil partial region  502  and reaching the second divided pixel  202  are, for example, as illustrated in  FIG. 24H  to  FIG. 24J .  FIG. 24H  is the point image intensity distribution of the case where the image pickup element  122  is located at the first position  2404 .  FIG. 24I  is the point image intensity distribution of the case where the image pickup element  122  is located at the second position  2405 .  FIG. 24J  is the point image intensity distribution of the case where the image pickup element  122  is located at the third position  2406 . The X axis represents the horizontal direction of the image pickup element  122 , and the vertical axis represents the light-receiving intensity. Note that, in  FIG. 24H  to  FIG. 24J , the point image intensity distributions in the horizontal direction of the image pickup element  122  are illustrated as an example. 
     The point image intensity distribution of the light fluxes passing through the pupil region  500  including the first pupil partial region  501  and the second pupil partial region  502  and reaching the image pickup pixel  200  including the first divided pixel  201  and the second divided pixel  202  is, for example, as illustrated in  FIG. 22A  to  FIG. 22C . 
       FIG. 22A  to  FIG. 22C  are schematic diagrams for illustrating the point image intensity distributions.  FIG. 22A  is the point image intensity distribution of the case where the image pickup element  122  is located at the first position  2404 .  FIG. 22B  is the point image intensity distribution of the case where the image pickup element  122  is located at the second position  2405 .  FIG. 22C  is the point image intensity distribution of the case where the image pickup element  122  is located at the third position  2406 . The X axis represents the horizontal direction of the image pickup element  122 , and the vertical axis represents the light-receiving intensity. Note that, in  FIG. 22A  to  FIG. 22C , the point image intensity distributions in the horizontal direction of the image pickup element  122  are illustrated as an example. 
     In this manner, the point image intensity distributions of the plurality of defocus positions are acquired (Step S 2101 ). 
     Next, a best image plane position is calculated (Step S 2102 ). The best image plane position (first in-focus position) is determined based on a contrast evaluation value calculated based on point image intensity distributions  2201 ,  2202 , and  2203  of the plurality of defocus positions. 
       FIG. 23  is a schematic diagram for illustrating the contrast evaluation values. The lateral axis represents the position of the image pickup element  122  in the Z axis direction, that is, the sensor position, and the vertical axis represents the contrast evaluation value.  FIG. 23  is obtained by plotting the contrast evaluation values calculated based on the point image intensity distributions  2201 ,  2202 , and  2203  of the respective sensor positions  2404 ,  2405 , and  2406 . Reference symbol  2301  represents a contrast evaluation value based on the point image intensity distributions  2201 ,  2202 , and  2203  in the horizontal direction of the image pickup element  122 . That is, reference symbol  2301  represents a contrast evaluation value of a horizontal component. Reference symbol  2302  represents a contrast evaluation value based on the point image intensity distributions in the vertical direction of the image pickup element  122 . That is, reference symbol  2302  represents a contrast evaluation value of a vertical component. 
     The sensor position obtained when the contrast evaluation value  2301  of the horizontal component takes a peak value is calculated as the best image plane position based on the horizontal component. Further, the sensor position obtained when the contrast evaluation value  2302  of the vertical component takes a peak value is calculated as the best image plane position based on the vertical component. In order to calculate the best image plane position for the object at high accuracy, the best image plane position is calculated based on a vertical and lateral component ratio of the object. The vertical and lateral component ratio of the object is calculated based on a ratio between the peak value of the contrast evaluation value of the vertical component of the image pickup signal and the peak value of the contrast evaluation value of the horizontal component of the image pickup signal. Based on the vertical and lateral component ratio of the object thus calculated, the best image plane position based on the horizontal component and the best image plane position based on the vertical component are weighted, to thereby calculate the best image plane position. 
     In order to calculate the best image plane position with respect to the object at high accuracy, the frequency band used when the contrast evaluation value is calculated is selected based on the frequency characteristics of the image pickup signal. Specifically, the contrast evaluation value of the image pickup signal obtained when the filtering is performed with use of a high pass filter is compared with the contrast evaluation value of the image pickup signal obtained when the filtering is performed with use of a low pass filter. When the contrast evaluation value is larger in the case where the high pass filter is used than in the case where the low pass filter is used, the frequency band included in a large amount in the object is considered to be a high band. In this case, the high band is selected as the frequency band used when the contrast evaluation value of the point image intensity distribution is calculated. On the other hand, when the contrast evaluation value is larger in the case where the low pass filter is used than in the case where the high pass filter is used, the frequency band included in a large amount in the object is considered to be a low band. In this case, the low band is selected as the frequency band used when the contrast evaluation value of the point image intensity distribution is calculated. 
     In this manner, the best image plane position (first in-focus position) is calculated (Step S 2102 ). 
     Next, a focus detection defocus position (second in-focus position) is calculated (Step S 2103 ). Specifically, the focus detection defocus position is calculated by performing correlation computing with use of point image intensity distributions  2424   a ,  2424   b ,  2425   a ,  2425   b ,  2426   a , and  2426   b  as illustrated in  FIG. 24H  to  FIG. 24J . 
     Note that, the correlation computing may be performed with use of a signal obtained by convolution of the signal of the object and the point image intensity distribution, to thereby calculate the focus detection defocus position. 
     Further, in this case, the focus detection defocus position is calculated by performing correlation computing, but the focus detection defocus position is not limited to be calculated by performing correlation computing. The focus detection defocus position may be obtained by other method such as a contrast detection method. 
     In this manner, the focus detection defocus position (second in-focus position) is calculated (Step S 2103 ). 
     Next, the correction value is calculated (Step S 2104 ). This correction value refers to a difference between the best image plane position (first in-focus position) calculated in Step S 2102  and the focus detection defocus position (second in-focus position) calculated in Step S 2103 . With use of this correction value, a defocus offset to be described later can be corrected. Note that, the defocus offset is described in detail later. The calculated correction value is recorded in, for example, the EEPROM  125   c  or the lens memory  118 . 
     Next, the defocus amount is corrected with use of the calculated correction value (Step S 2105 ). That is, with use of the correction value calculated in Step S 2104 , the defocus amount calculated in Step S 706  of  FIG. 7  is corrected. 
     In this manner, the defocus amount correction processing is ended. 
     [Defocus Offset Generation Principle] 
     Next, a defocus offset generation principle is described.  FIG. 24A  to  FIG. 24J  are schematic diagrams for illustrating the defocus offset generation principle. 
       FIG. 24A  to  FIG. 24E  are illustrations of a case where the lens aberration is absent, and  FIG. 24F  to  FIG. 24J  are illustrations of a case where the lens aberration is present. The X axis of  FIG. 24A  and  FIG. 24F  represents the horizontal direction of the exit pupil plane. Reference symbols  2401  to  2406  represent positions of the image pickup element  122 . Reference symbols  2401  and  2404  correspond to rear focus positions, reference symbols  2402  and  2405  correspond to best image plane positions, and reference symbols  2403  and  2406  correspond to front focus positions. 
       FIG. 24B  and  FIG. 24G  are illustrations of defocus curves  2411   a  and  2411   b . The lateral axis of  FIG. 24B  and  FIG. 24G  represents the Z axis direction, that is, the optical axis direction, and the vertical axis of  FIG. 24B  and  FIG. 24G  represents the defocus amount def. 
       FIG. 24C  to  FIG. 24E  and  FIG. 24H  to  FIG. 24J  are illustrations of the point image intensity distributions. The lateral axis represents the X axis direction, that is, the horizontal direction of the image pickup element  122 , and the vertical axis represents the light-receiving intensity. 
       FIG. 24C  is an illustration of point image intensity distributions  2421   a  and  2421   b  at the rear focus position  2401 . Reference symbol  2421   a  represents the point image intensity distribution of the light fluxes passing through the first pupil partial region  501 , and reference symbol  2421   b  represents the point image intensity distribution of the light fluxes passing through the second pupil partial region  502 . 
       FIG. 24D  is an illustration of the point image intensity distributions  2422   a  and  2422   b  at the best image plane position  2402 . Reference symbol  2422   a  represents the point image intensity distribution of the light fluxes passing through the first pupil partial region  501 , and reference symbol  2422   b  represents the point image intensity distribution of the light fluxes passing through the second pupil partial region  502 . 
       FIG. 24E  is an illustration of point image intensity distributions  2423   a  and  2423   b  at the front focus position  2403 . Reference symbol  2423   a  represents the point image intensity distribution of the light fluxes passing through the first pupil partial region  501 , and reference symbol  2423   b  represents the point image intensity distribution of the light fluxes passing through the second pupil partial region  502 . 
       FIG. 24H  is an illustration of the point image intensity distributions  2424   a  and  2424   b  at the rear focus position  2404 . Reference symbol  2424   a  represents the point image intensity distribution of the light fluxes passing through the first pupil partial region  501 , and reference symbol  2424   b  represents the point image intensity distribution of the light fluxes passing through the second pupil partial region  502 . 
       FIG. 24I  is an illustration of the point image intensity distributions  2425   a  and  2425   b  at the best image plane position  2405 . Reference symbol  2425   a  represents the point image intensity distribution of the light fluxes passing through the first pupil partial region  501 , and reference symbol  2425   b  represents the point image intensity distribution of the light fluxes passing through the second pupil partial region  502 . 
       FIG. 24J  is an illustration of the point image intensity distributions  2426   a  and  2426   b  at the front focus position  2406 . Reference symbol  2426   a  represents the point image intensity distribution of the light fluxes passing through the first pupil partial region  501 , and reference symbol  2426   b  represents the point image intensity distribution of the light fluxes passing through the second pupil partial region  502 . 
     When the lens aberration is absent, as is understood through comparison between  FIG. 24C  and  FIG. 24E , the point image intensity distribution  2421   a  at the rear focus position  2401  and the point image intensity distribution  2423   a  at the front focus position  2403  are line symmetric with respect to the vertical axis. Further, the point image intensity distribution  2421   b  at the rear focus position  2401  and the point image intensity distribution  2423   b  at the front focus position  2403  are line symmetric with respect to the vertical axis. Further, as illustrated in  FIG. 24D , the point image intensity distribution  2422   a  at the best image plane position  2402  and the point image intensity distribution  2422   b  at the best image plane position match with each other. As illustrated in  FIG. 24B , the defocus offset is not generated between the true defocus position and the focus detection defocus position calculated based on the point image intensity distributions  2421   a ,  2421   b ,  2422   a ,  2422   b ,  2423   a , and  2423   b.    
     When the lens aberration is present, as is understood through comparison between  FIG. 24H  and  FIG. 24J , the point image intensity distribution  2424   a  at the rear focus position  2404  and the point image intensity distribution  2426   a  at the front focus position  2406  are not line symmetric with respect to the vertical axis. Further, the point image intensity distribution  2424   b  at the rear focus position  2404  and the point image intensity distribution  2426   b  at the front focus position  2406  are not line symmetric with respect to the vertical axis. Further, as is understood from  FIG. 24I , the point image intensity distribution  2425   a  at the best image plane position  2405  and the point image intensity distribution  2425   b  at the best image plane position  2405  do not match with each other. Further, as illustrated in  FIG. 24G , a defocus offset dz is generated between the true defocus position and the focus detection defocus position calculated based on the point image intensity distributions. 
     Note that, in this embodiment, a case where the point image intensity distributions are used for the defocus amount correction is described as an example, but the point image intensity distributions can be used for image processing and the like. 
     As described above, according to this embodiment, based on the lens light field data and the sensor light-receiving intensity characteristic, the point image intensity distributions of a plurality of sensor positions in the optical axis direction are generated. Then, based on the point image intensity distribution of the light fluxes passing through the pupil region  500  that is the entire region of the exit pupil of the photographing lens  105 , the best image plane position (first in-focus position) is calculated. Further, based on the point image intensity distribution of the light fluxes passing through the first pupil partial region  501  and the point image intensity distribution of the light fluxes passing through the second pupil partial region  502 , the focus detection defocus position (second in-focus position) is calculated. Then, based on the difference between the first in-focus position and the second in-focus position, the correction value is calculated, to thereby correct the defocus amount obtained through the phase-difference focus detection by this correction value. Then, based on the defocus amount corrected by this correction value, the photographing lens  105  is driven for focusing. The point image intensity distribution is obtained based on the lens light field data specific to the photographing lens  105  and the sensor light-receiving intensity characteristic specific to the image pickup apparatus main body  120 . Therefore, the correction value obtained based on the point image intensity distribution is a correction value taking into consideration of the manufacturing variations of the photographing lens  105  and the image pickup apparatus main body  120 . Therefore, according to this embodiment, an image pickup apparatus capable of performing auto-focus at high accuracy can be provided. Further, by holding the acquired correction value, the defocus amount can be rapidly corrected with use of the correction value, which enables further rapid auto-focus at high accuracy. 
     [Second Embodiment] 
     Next, an image pickup system according to a second embodiment of the present invention is described with reference to the drawings.  FIG. 25  is a schematic diagram for illustrating the configuration of the image pickup system according to this embodiment. The same components as the image pickup apparatus according to the first embodiment illustrated in  FIG. 1  to  FIG. 24J  are denoted by the same reference symbols, and the description thereof is omitted or simplified herein. 
     The image pickup system according to this embodiment is configured to hold the sensor light-receiving intensity characteristic and the lens light field data on the network, and generate the point image intensity distribution by the point image intensity distribution generating unit on the network. 
     As illustrated in  FIG. 25 , a processor  2503  including an optical characteristic information storage unit (optical characteristic information storage device, optical characteristic information storage portion)  2501  and a point image intensity distribution generating unit (point image intensity distribution generating portion)  2502  is provided on the network. The optical characteristic information storage unit  2501  includes a sensor light-receiving intensity characteristic storage unit (sensor light-receiving intensity characteristic storage portion)  2501   a  and a lens light field data storage unit (lens light field data storage portion)  2501   b . The optical characteristic information storage unit  2501  and the point image intensity distribution generating unit  2502  are connected to each other. The sensor light-receiving intensity characteristic is stored in the sensor light-receiving intensity characteristic storage unit  2501   a . The lens light field data is stored in the lens light field data storage unit  2501   b.    
     The image pickup apparatus  10  may access the processor  2503  on the network through communication. 
     In this manner, the image pickup system according to this embodiment is formed. 
     According to this embodiment, the sensor light-receiving intensity characteristic and the lens light field data, which have a large amount of information, are held on the network, and hence the data amount to be held by the image pickup apparatus  10  and the photographing lens  105  can be reduced. 
     Note that, the configuration of the image pickup apparatus  10 , the focus detection processing, the point image intensity distribution generation processing, and the defocus amount correction processing according to this embodiment are similar to those in the above-mentioned first embodiment, and hence the description thereof is omitted herein. Note that, in order to enable the image pickup apparatus  10  to access the optical characteristic information storage unit  2501  and the point image intensity distribution generating unit  2502  on the network, the image pickup apparatus  10  is preferred to include a communication function (communication portion) (not shown). Such a communication function (communication portion) may be a wireless communication function (wireless communication portion) or a wired communication function (wired communication portion). 
     Next, the operation of the image pickup system according to this embodiment is described with reference to  FIG. 26 .  FIG. 26  is a flow chart for illustrating the schematic operation of the image pickup system according to this embodiment. 
     First, sensor information and lens information are acquired (Step S 2601 ). Specifically, lens information (lens ID) is acquired from the lens unit  100 , and sensor information (sensor ID) is acquired from the image pickup apparatus main body  120 . The lens ID refers to an ID given to the photographing lens  105 , and the sensor ID refers to an ID given to the image pickup element  122  incorporated in the image pickup apparatus main body  120 . Such sensor information and lens information are transmitted from the image pickup apparatus  10  to the processor  2503  on the network. In this manner, the processor  2503  acquires the sensor information and the lens information. 
     Next, the processor  2503  acquires a sensor light-receiving intensity characteristic (Step S 2602 ). The sensor light-receiving intensity characteristic corresponding to each sensor ID is stored in advance in the sensor light-receiving intensity characteristic storage unit  2501   a . Based on the sensor information (sensor ID) acquired in Step S 2601 , the sensor light-receiving intensity characteristic specific to the image pickup element  122  is acquired from the sensor light-receiving intensity characteristic storage unit  2501   a.    
     Next, the processor  2503  acquires lens light field data (Step S 2603 ). The lens light field data corresponding to each lens ID is stored in advance in the lens light field data storage unit  2501   b . Based on the lens information (lens ID) acquired in Step S 2601 , the lens light field data specific to the photographing lens  105  is acquired from the lens light field data storage unit  2501   b.    
     Next, the processor  2503  performs the point image intensity distribution generation processing (Step S 2604 ). Specifically, based on the sensor light-receiving intensity characteristic acquired in Step S 2602  and the lens light field data acquired in Step S 2603 , the point image intensity distribution is generated by the point image intensity distribution generating unit  2502 . 
     Next, the correction value is calculated (Step S 2605 ). Specifically, the correction value is calculated based on the point image intensity distribution generated in Step S 2604 . The calculation of the correction value is similar to the calculation of the correction value of the first embodiment, and hence the description thereof is omitted herein. The correction value is calculated in, for example, the image pickup apparatus  10 . Note that, the correction value may be calculated on the processor  2503  side. 
     Next, the calculated correction value is recorded (Step S 2606 ). Specifically, the correction value calculated in Step S 2605  is recorded in the lens memory  118  or the EEPROM  125   c  of the image pickup apparatus  10 . 
     This correction value may be calculated and recorded in advance for all combinations obtained by changing parameters such as the image height, the aperture value, the lens zoom state, and the lens focus state, or may be calculated and recorded through communication each time as necessary. 
     Further, in this embodiment, a case where the correction value is calculated based on the point image intensity distribution so as to record the correction value is described as an example, but the point image intensity distribution may be recorded and used for image processing or the like. 
     &lt;Other Embodiments&gt; 
     Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2014-266496, filed Dec. 26, 2014 which is hereby incorporated by reference wherein in its entirety.