Patent Publication Number: US-9906709-B2

Title: Image pickup apparatus having image pickup element including a plurality of pixels, each pixel including a plurality of photodiodes corresponding to microlens, lens unit to be removably mounted on image pick up apparatus, and methods of controlling image pickup apparatus and lens unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 14/243,161, filed Apr. 2, 2014 the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an image pickup apparatus including different types of focus detection units. 
     Description of the Related Art 
     Conventionally, as focus detection methods of an image pickup apparatus, a phase difference detection method which detects a pair of image signals obtained from a light beam that has passed through different pupil regions of an optical system and a contrast detection method which uses a contrast component of an image signal have been known. In addition, as one of the phase difference detection methods, an imaging plane phase difference detection method has been known which performs focus detection by the phase difference detection method by using an output from an image pickup element. 
     Japanese Patent Laid-Open No. (“JP”) 2001-083407 discloses, as a focus detection method adopting the imaging plane phase difference detection method, a configuration in which each of a plurality of photodiodes (hereinafter, referred to as “PDs”) provided to its corresponding micro lens receives light from pupil regions different from each other. Such a configuration enables focus detection by the phase difference detection method by comparing outputs of two PDs. 
     The image pickup apparatus has been known which allows a user to select an AF method from a plurality of AF methods such as the phase difference detection method and the contrast method. JP 2012-118154 discloses a configuration which selects the contrast detection method using a wobbling lens because narrowing down an aperture stop results in a decrease in accuracy of autofocusing (AF method) by the phase difference detection method. 
     In the focus detection by the imaging plane phase difference detection method, some lenses suffer from a displacement of an in-focus position (hereinafter, referred to as a “best focus (BF) shift”) which is caused by an aberration and a chromatic aberration of an object light beam of a shot image and that of the focus detection. Due to this drawback, some interchangeable lenses designed to be mounted on an image pickup apparatus may not be able to satisfy an in-focus accuracy allowable as a still image. If an image pickup apparatus stores a correction values (hereinafter, referred to as a “best focus (BF) correction value”) designed to correct the BP shift for every type of interchangeable lens, an extremely large amount of data capacity is required. Furthermore, in order to make it possible to correct the BF shift for interchangeable lenses to be released in the future, firmware updating and other measures are required and this approach is inefficient. 
     SUMMARY OF THE INVENTION 
     The present invention provides an image pickup apparatus, a lens unit, and methods of controlling the image pickup apparatus and the lens unit which are capable of performing an appropriate focus detection in which an influence of a focus shift caused by an aberration is suppressed. 
     An image pickup apparatus as one aspect of the present invention is an image pickup apparatus on which a lens unit is to be removably mounted, includes an image pickup element including a plurality of pixels, each of which includes a plurality of photodiodes corresponding to a micro lens, a first focus detection unit configured to perform a focus detection by a contrast detection method based on a signal output from the image pickup element, a second focus detection unit configured to perform a focus detection by a phase difference detection method based on a pair of image signals output from the image pickup element, and a control unit configured to perform a focus control based on an in-focus position detected by one of the first focus detection unit and the second focus detection unit, and the control unit is configured to receive, from the mounted lens unit, first information related to a displacement of the in-focus position by the phase difference detection method caused by an aberration of an image pickup optical system of the lens unit and determine whether to use the second focus detection unit for the focus control according to the first information. 
     A lens unit as another aspect of the present invention is a lens unit to be removably mounted on an image pickup apparatus, includes an image pickup optical system, and a lens controller configured to send data to the mounted image pickup apparatus, the lens controller is configured to send, to the image pickup apparatus, first information related to a displacement of an in-focus position by the phase difference detection method caused by an aberration of the image pickup optical system, and the first information indicates that there is the displacement of the in-focus position and contains information on a correction value to correct the displacement of the in-focus position. 
     A method of controlling an image pickup apparatus as another aspect of the present invention is a method of controlling an image pickup apparatus on which a lens unit is to be removably mounted, the image pickup apparatus includes an image pickup element including a plurality of pixels, each of which includes a plurality of photodiodes corresponding to a micro lens, the method includes a first focus detection step of performing a focus detection by a contrast detection method based on a signal output from the image pickup element, a second focus detection step of performing a focus detection by a phase difference detection method based on a pair of image signals output from the image pickup element, and a control step of performing a focus control based on an in-focus position detected in one of the first focus detection step and the second focus detection step, and, in the control step, first information related to a displacement of the in-focus position by the phase difference detection method caused by an aberration of an image pickup optical system of the mounted lens unit is received from the lens unit and then whether to use a result of the second focus detection step for the focus control is determined according to the first information. 
     A method of controlling a lens unit as another aspect of the present invention is a method of controlling a lens unit removably mounted on an image pickup apparatus, the lens unit includes an image pickup optical system, the method includes a control step of sending data to the mounted image pickup apparatus, in the control step, first information related to a displacement of an in-focus position by the phase difference detection method caused by an aberration of the image pickup optical system is sent to the image pickup apparatus, and the first information indicates that there is the displacement of the in-focus position and contains information on a correction value to correct the displacement of the in-focus position. 
     Further features and aspects 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 schematic configuration diagram of an image pickup system in a first embodiment. 
         FIG. 2  is a circuit configuration diagram of the image pickup system in the first embodiment. 
         FIG. 3  is a flowchart illustrating a procedure of shooting processing in the first embodiment. 
         FIG. 4  is a flowchart illustrating a procedure of imaging plane phase difference AF processing in the first embodiment. 
         FIG. 5  is a flowchart illustrating a procedure of contrast AF processing in the first embodiment. 
         FIG. 6  is a flowchart illustrating a procedure of first selection processing of an AF method in the first embodiment. 
         FIG. 7  is a flowchart illustrating a procedure of second selection processing of an AF method in a second embodiment. 
         FIG. 8  is a flowchart illustrating a procedure of registration processing of a focus correction value in the second embodiment. 
         FIG. 9  is a flowchart illustrating a procedure of a lens communication of a new-communication compatible lens in the first embodiment. 
         FIG. 10  is a flowchart illustrating a procedure of a lens communication of a new-communication incompatible lens in the first embodiment. 
         FIG. 11  is a table which is relevant to a best focus correction stored in an image pickup apparatus in each of the first and second embodiments. 
         FIG. 12  is a diagram illustrating definitions of the lens communication in each of the first and second embodiments. 
         FIG. 13A  is a diagram illustrating an example of a pixel configuration where an imaging plane phase difference detection method is not to be used. 
         FIG. 13B  is a diagram illustrating an example of a pixel configuration where the imaging plane phase difference detection method is to be used. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described in detail below with reference to the attached drawings. 
     First Embodiment 
     First of all, referring to  FIG. 1 , the configuration of an image pickup system in the first embodiment of the present invention will be described.  FIG. 1  is a schematic configuration diagram of the image pickup system in this embodiment. 
     In  FIG. 1 , the image pickup system includes an image pickup apparatus  100  (an image pickup apparatus body, or a camera) and an interchangeable lens  200  (a lens unit) removably mounted on the image pickup apparatus  100 . As described later, the image pickup apparatus  100  include an image pickup element with a plurality of pixels, each of which has a plurality of photodiodes arranged underneath a micro lens, and the photodiodes receive light from pupil regions (divided pupil regions) different from each other in an image pickup optical system including a lens  202 . In this configuration, the image pickup apparatus  100  is capable of performing a focus detection method by using a phase difference detection method (an imaging plane phase difference detection method) while capturing an image. In addition, the image pickup apparatus  100  performs a focus detection by a contrast detection method by using a contrast detection method to search a position of a focus lens at which a contrast evaluation value generated from an image signal output from the image pickup element reaches a peak. The image pickup system of this embodiment is not limited to this, and is also applicable to an image pickup system constituted by the image pickup apparatus  100  to which a lens unit corresponding to the interchangeable lens  200  is integrally attached. 
     In the image pickup apparatus  100 , reference numeral  101  denotes an erect normal image optical system constituting a finder optical system, reference numeral  102  an eyepiece. Reference numeral  103  denotes a finder screen, and reference numeral  104  denotes a main mirror configured to deflect a part of a light beam (an image-pickup light beam) to the finder optical system (the erect normal image optical system  101 ). Reference numeral  105  denotes a sub-mirror configured to deflect the image-pickup light beam that has passed through the main mirror  104  to a focus detection apparatus  109 . 
     Reference numeral  106  denotes an image pickup element. The image pickup element  106  is configured to photoelectrically convert an object image formed by receiving a light beam from the object which has passed through the image pickup optical system provided inside the interchangeable lens  200  to an electrical signal to output the electrical signal. The image pickup element  106  of this embodiment includes pixels, each of which has two photodiodes, and thus is capable of generating an image signal to be used for the focus detection by the imaging plane phase difference detection method.  FIGS. 13A and 13B  schematically illustrate a pixel configuration incompatible with the imaging plane phase difference detection method and that compatible with the imaging plane phase difference detection method, respectively. In this embodiment, a Bayer-array primary color filter is provided in each of the pixel configurations. In the pixel configuration compatible with the imaging plane phase difference detection method illustrated in  FIG. 13B , each pixel of  FIG. 13A  is divided into two parts in a horizontal direction to provide two photodiodes A and B. The manner of the division illustrated in  FIG. 13B  is an example, and hence other manners may be used, the number of divisions may be changed, or a different manner of the division may be applied depending on a pixel. 
     The micro lens divides the light beam entering each pixel and the two photodiodes provided in the pixel receives the divided light beams respectively, and thus two signals of an image pickup signal and an AF signal can be obtained by one pixel. That is, signals (signals A and B) obtained by the two photodiodes A and B (pixels A and B) in each pixel are two image signals for AF (the AF signals), and an addition signal (the signal A+the signal B) is the image pickup signal. As a pair of image signals to be used in an ordinary phase difference detection method is generated by a pair of line sensors including a plurality of pixels, a pair of signals to be used in the imaging plane phase difference detection method is obtained based on outputs of a plurality of the pixels A and the pixels B. A controller  112  described later performs a correlation calculation for the pair of image signals based on the AF signal to calculate an image shift amount and various kinds of reliability information. 
     Reference numeral  107  denotes a shutter apparatus configured to shield the image pickup element  106 . Reference numeral  108  denotes a built-in strobe included inside the image pickup apparatus  100 . The built-in strobe  108  not only illuminates an object during a shooting when an external strobe is not attached, but also functions as an auxiliary light which irradiates the object during the focus detection. 
     Reference numeral  109  denotes the focus detection apparatus. The focus detection apparatus  109  includes a plurality of sensors (line sensors), each of which has a plurality of light receiving portions, and is configured to perform the focus detection by the phase difference detection method. More specifically, the focus detection apparatus  109  is configured to divide a light beam (into two) which has passed through an exit pupil of the focus lens included in the lens  202  to cause each pair of line sensors to receive the divided light beams. 
     In this embodiment, two image signals obtained based on the divided light beams are defined as an image signals A and B. The focus detection apparatus  109  is configured to detect a shift amount of output signals depending on light receiving amounts of the image signals A and B, i.e. a shift amount of relative positions of the light beams in a division direction, to determine a defocus amount of the focus lens. Therefore, a charge accumulation operation by the focus detection apparatus  109  makes it possible to obtain an amount and a direction where the focus lens is to be moved (a movement amount and a movement direction) to drive the focus lens. 
     Reference numeral  110  denotes a photometry apparatus configured to measure an exposure of the image pickup apparatus  100 . Reference numeral  111  denotes a lens configured to form an image of the light beam obtained from the object on the photometry apparatus  110 . Reference numeral  112  denotes the controller (a microprocessor, or a camera CPU) configured to control the image pickup apparatus  100 . The controller  112  functions as a first focus detection unit configured to perform the focus detection by the contrast detection method. The controller  112  also functions as a second focus detection unit configured to perform the focus detection by the phase difference detection method (the imaging plane phase difference detection method) based on the AF signal from the image pickup element  106 . Moreover, the controller  112  functions as a control unit configured to select either of the first focus detection unit or the second focus detection unit according to focus information of the interchangeable lens  200  with respect to the image pickup element  106  to perform a focus control (an in-focus control). 
     Reference numeral  113  denotes an accessory shoe on which an external apparatus such as an external strobe is to be attached. Reference numeral  114  denotes a Fresnel lens of the built-in strobe  108 . Reference numeral  115  denotes a finder display unit provided inside the image pickup apparatus  100  and configured to display information on an optical finder in a superimposed manner. Reference numeral  116  denotes an external display unit configured to display various kinds of information on the external apparatus of the image pickup apparatus  100 . 
     Reference numeral  200  denotes the interchangeable lens (the lens unit) including the image pickup optical system. Reference numeral  201  denotes a lens controller (a microprocessor, or a lens CUP) configured to control the interchangeable lens  200 . The lens controller  201  also communicates with the controller  112  of the image pickup apparatus  100  via a communication unit. Reference numeral  202  denotes the lens configured to form an object image on the image pickup element  106 . The lens  202  includes the focus lens capable of moving in an optical axis direction to perform focusing. Reference numeral  203  denotes an aperture stop apparatus configured to adjust a light intensity. 
     Subsequently, referring to  FIG. 2 , the circuit configuration of the image pickup system (the image pickup apparatus  100  and the interchangeable lens  200 ) will be described.  FIG. 2  is a circuit configuration diagram (a block diagram) of the image pickup system. 
     A motor drive circuit  1  drives a movable portion of the image pickup apparatus  100 . A photometry portion  2  measures a luminance of the object. The photometry portion  2  is included in the photometry apparatus  110  illustrated in  FIG. 1 . A focus detection portion  3  detects a focus state of the interchangeable lens  200 . The focus detection portion  3  is included in the focus detection apparatus  109  illustrated in  FIG. 1 . A shutter control circuit  4  controls an exposure amount of the image pickup apparatus  100 . The shutter control circuit  4  is included in the shutter apparatus  107  illustrated in  FIG. 1 . 
     An aperture stop control circuit  5  controls the aperture stop apparatus  203  illustrated in  FIG. 1  to control the light beam incident on the image pickup apparatus  100 . A display apparatus  6  including the finder display unit  115  and the external display unit  116 , which are illustrated in  FIG. 1 , displays a state of the image pickup apparatus  100 . A strobe control circuit  7  controls the built-in strobe  108  illustrated in  FIG. 1 . A storage circuit  8  (a storage unit) stores a setting status of the image pickup apparatus  100 . An image pickup circuit  9  controls the image pickup element  106  to perform image pickup processing. Reference numeral  10  denotes a lens communication circuit configured to communicate with the lens controller  201  (the lens CPU) of the interchangeable lens  200  mounted on the image pickup apparatus  100 . Reference numeral  11  denotes a communication circuit configured to communicate with the external apparatus such as the external strobe. Reference numeral  12  denotes a switch (SW 1 ) configured to start an image pickup preparation operation. Reference numeral  13  denotes a switch (SW 2 ) configured to start an image pickup operation. Reference numeral  14  denotes a dial/switch portion configured to register various settings and modes of the image pickup apparatus  100  and a best focus correction value. 
     Reference numeral  21  denotes a lens drive circuit configured to drive the interchangeable lens  200 . A lens position detection circuit  22  is configured to detect a position of the interchangeable lens  200 . A lens focal length detection circuit  23  is configured to detect a focal length set in the interchangeable lens  200 . Reference numeral  24  denotes a storage circuit (a storage unit) configured to store a set value of the interchangeable lens  200 . Reference numeral  25  denotes an aperture stop drive circuit configured to drive the aperture stop. The aperture stop drive circuit  25  is included in the aperture stop apparatus  203  illustrated in  FIG. 1 . Reference numeral  26  denotes a lens communication circuit configured to communicate with the controller  112  (the camera CPU) of the image pickup apparatus  100 . 
     Next, referring to  FIG. 3 , image pickup processing by the image pickup system of this embodiment will be described.  FIG. 3  is a flowchart illustrating a procedure of the shooting processing in this embodiment. Each step of  FIG. 3  is mainly performed based on a command (an instruction) of the controller  112  (the camera CPU). 
     First, at step S 301 , the controller  112  determines whether or not the switch  12  (the SW 1 ) of the image pickup apparatus  100  is turned on. The controller  112  continues step S 301  until the switch  12  (the SW 1 ) is turned on, and the flow proceeds to step S 302  when the switch (the SW 1 ) is turned on. Then, at step S 302 , the controller  112  performs first selection processing of the AF method. In the first selection processing of the AF method, the controller  112  selects either of the first focus detection unit or the second focus detection unit according to focus information of the interchangeable lens  200 . In this embodiment, the focus information includes information related to a displacement (shift) of an in-focus position (a best focus shift, or a BF shift) that is generated by an aberration or a chromatic aberration of object light beams of a shot image and the focus detection. The details of the first selection processing of the AF method will be described later. 
     Subsequently, at step S 303 , the controller  112  determines whether or not the AF method selected at step S 302  is the imaging plane phase difference AF. When the controller  112  determines that the AF method is the imaging plane phase difference AF at step S 303 , the flow proceeds to step S 304  and the controller  112  performs the imaging plane phase difference AF. The details of the imaging plane phase difference AF will be described later. On the other hand, when the controller  112  determines that the AF method is not the imaging plane phase difference AF at step S 303 , the flow proceeds to step S 305  and the controller  112  performs the contrast AF processing. The details of the contrast AF processing will be described later. 
     After the imaging plane phase difference AF processing at step S 304  or the contrast AF processing at step S 305  is performed, the flow proceeds to step S 306 . At step S 306 , the controller  112  determines whether or not the switch  12  (the SW 1 ) of the image pickup apparatus  100  is on. The flow returns to step S 301  when the switch  12  (the SW 1 ) is turned off at step S 306 . 
     On the other hand, the flow proceeds to step S 307  when the switch  12  (the SW 1 ) is on at step S 306 . At step  307 , the controller  112  determines whether or not the switch  13  (the SW 2 ) of the image pickup apparatus  100  is turned on. The flow returns to step S 306  when the switch  13  (the SW 2 ) is off at step S 307 . 
     On the other hand, the flow proceeds to step S 308  when the switch  13  (the SW 2 ) is turned on at step S 307 . At step S 308 , the controller  112  controls the shutter control circuit  4  to prepare for a shooting (capturing an image). Subsequently, at step S 309 , the controller  112  controls the image pickup circuit  9  to perform recording processing. This series of shooting processing ends upon completion of the above steps. 
     Subsequently, referring to  FIG. 4 , the imaging plane phase difference AF processing performed at step S 304  of  FIG. 3  will be described.  FIG. 4  is a flowchart illustrating a procedure of the imaging plane phase difference AF processing in this embodiment. Each step of  FIG. 4  is mainly performed based on a command (an instruction) of the controller  112  (the camera CPU). 
     First, at step S 401 , the controller  112  obtains an image signal for the AF within a range arbitrarily set. After that, at step S 402 , the controller  112  calculates a correlation amount based on the image signal obtained at step S 401 . Subsequently, at step S 403 , the controller  112  calculates a correlation variation amount based on the correlation amount calculated at step S 402 . 
     Next, at step S 404 , the controller  112  calculates an out-of-focus amount based on the correlation variation amount calculated at step S 403 . After that, at step S 405 , the controller  112  calculates a reliability of the out-of-focus amount calculated at step S 404  (a value indicating a reliability level of the calculated out-of-focus amount). As an evaluation value of the reliability, for example, a value of an S level (SELECT LEVEL) disclosed in JP2007-052072 is used. Subsequently, at step S 406 , the controller  112  converts the out-of-focus amount calculated at step S 404  to a defocus amount (DEF). 
     Next, at step S 407 , the controller  112  determines whether or not best focus correction (BF correction) is to be performed. The flow proceeds to step S 408  when the BF correction is to be performed, that is, a BF correction flag is set to 1. On the other hand, the flow proceeds to step S 409  when the BF correction is not to be performed, that is, the BF correction flag is not set to 1. 
     At step S 408 , the controller  112  adds a BF correction value (a variable BFcomp) obtained at step S 611  or S 617  of  FIG. 6 , which is described later, to the defocus amount (the DEF) calculated at step S 406 . After that, at step S 409 , the controller  112  performs an in-focus determination, i.e. determines whether or not an in-focus state is obtained. When the controller  112  determines that the in-focus state is obtained at step S 409 , the flow proceeds to step S 411  and the controller  112  ends the imaging plane phase difference detection AF processing. 
     On the other hand, the flow proceeds to step S 410  when the controller  112  determines that the in-focus state is not obtained at step S 409 . At step S 410 , the focus lens is driven by an amount corresponding to the defocus amount (DEF) calculated at step S 406  or S 408 , and then the flow returns to step S 401 . The driving of the focus lens is performed by the lens controller  201  (the lens CPU) which communicates with the controller  112  (the camera CPU) to control the lens drive circuit  21 . 
     Subsequently, referring to  FIG. 5 , the contrast AF processing performed at step S 305  of  FIG. 3  will be described.  FIG. 5  is a flowchart illustrating a procedure of the contrast AF processing in this embodiment. Each step of  FIG. 5  is mainly performed based on a command (an instruction) of the controller  112  (the camera CPU). 
     First, at step S 501 , the controller  112  obtains an image signal. After that, at step S 502 , the controller  112  calculates a contrast evaluation value based on the image signal obtained at step S 501 . Subsequently, at step S 503 , the controller  112  performs an in-focus determination, i.e. determines whether or not an in-focus state is obtained. 
     The flow proceeds to step S 504  when the controller  112  determines that the in-focus state is not obtained at step S 503 . At step S 504 , the focus lens is driven based on information on the contrast evaluation value obtained at step S 502 , and then the flow returns to step S 501 . The driving of the focus lens is performed by the lens controller  201  (the lens CPU) which communicates with the controller  112  to control the lens drive circuit  21 . 
     On the other hand, the flow proceeds to step S 505  when the controller  112  determines that the in-focus state is obtained at step S 503 . At step S 505 , the controller  112  calculates an in-focus position based on the contrast evaluation value. Subsequently, at step  506 , the focus lens is driven based on the information on the contrast evaluation value obtained at step S 502 . After that, the flow proceeds to step S 507  and the contrast AF processing ends. 
     Subsequently, referring to  FIG. 6 , the first selection processing of the AF method which is performed at step S 302  of  FIG. 3  will be described.  FIG. 6  is a flowchart illustrating a procedure of the first selection processing of the AF method in this embodiment. Each step of  FIG. 6  is mainly performed based on a command (an instruction) of the controller  112  (the camera CPU). 
     First, at step S 601 , the controller  112  clears a best focus correction flag (BF correction flag). After that, at step S 602 , the controller  112  sets the variable BFcomp to 0 (zero). Subsequently, at step S 603 , the controller  112  performs lens communication by a command A 0  (A 0  communication) to determine whether or not the mounted interchangeable lens  200  is a lens compatible with a new communication (a new-communication compatible lens). 
       FIG. 12  is a diagram illustrating the definition of each lens communication in this embodiment. The A 0  communication is communication performed by sending the command A 0  from the controller  112 . Upon receipt of the command A 0 , the lens controller  201  sends the command A 0 , as data  1 , to the controller  112  of the image pickup apparatus  100 , and then sends data, as data  2 , indicating whether or not the interchangeable lens  200  is the new-communication compatible lens. When the value of the data  2  is “00”, it indicates that the interchangeable lens  200  is a lens incompatible with the new communication (a new-communication incompatible lens). Similarly, when the value of the data  2  is “01”, it indicates that the interchangeable lens  200  is the new-communication compatible lens. 
     Subsequently, at step S 604  of  FIG. 6 , the controller  112  determines whether or not the mounted interchangeable lens  200  is the new-communication compatible lens based on the information obtained at step S 603 . The flow proceeds to step S 605  when the controller  112  determines that the mounted interchangeable lens  200  is the new-communication compatible lens. On the other hand, the flow proceeds to step S 613  when the controller  112  determines that the mounted interchangeable lens  200  is not the new-communication compatible lens (i.e. the interchangeable lens is the new-communication incompatible lens). 
     At step S 605 , the controller  112  performs lens communication by a command B 0  (B 0  communication) to determine whether or not there is a best focus shift (a BF shift) and a best focus correction value (a BF correction value) with respect to the attached interchangeable lens  200 . 
     As illustrated in  FIG. 12 , the B 0  communication is communication performed by sending the command B 0  from the controller  112 . Upon receipt of the command B 0 , the lens controller  201  sends the command B 0 , as data  1 , to the controller  112  of the image pickup apparatus  100 , and then sends data, as data  2 , indicating whether or not there is the BF shift and the BF correction value with respect to the mounted interchangeable lens  200 . When the value of the data  2  is “00”, it indicates that there is not the BF shift for the mounted interchangeable lens  200 . Similarly, when the value of the data  2  is “01”, it indicates that there is not the BF shift (and that there is the BF correction value) for the mounted interchangeable lens  200 . When the value of the data  2  is “02”, it indicates that there is the BF shift (and that there is not the BF correction value) for the mounted interchangeable lens  200 . 
     Subsequently, at step S 606  of  FIG. 6 , the controller  112  determines whether or not there is the BF shift with respect to the mounted interchangeable lens  200  based on the information obtained at step S 605 . That is, the controller  112  determines whether or not the value of the data  2  is “00”. The flow proceeds to step S 612  when the controller  112  determines that there is not the BF shift for the mounted interchangeable lens  200  (BF information=0, that is, the value of the data  2  is “00”) at step S 606 . On the other hand, the flow proceeds to step S 607  when the controller  112  determines that there is the BF shift for the mounted interchangeable lens  200  (BF information≠0, that is, the value of the data  2  is “01” or “02”) at step S 606 . 
     At step S 607 , the controller  112  determines whether or not there is the BF correction value with respect to the mounted interchangeable lens  200  based on the information obtained at step S 605 . That is, the controller  112  determines whether or not the value of the data  2  is “01”. The flow proceeds to step S 608  when the controller  112  determines that there is the BF shift (and that there is not the BF correction value) for the mounted interchangeable lens  200  (BF information* 1 , that is, the value of the data  2  is “02”) at step S 607 . At step S 608 , the controller  112  sets a focus detection method (an AF method) to the contrast AF. 
     On the other hand, the flow proceeds to step S 609  when the controller  112  determines that there is the BF shift (and that there is the BF correction value) for the mounted interchangeable lens  200  (BF information=1, that is, the value of the data  2  is “01”) at step S 607 . At step S 609 , the controller  112  perform lens communication by a command C 0  (C 0  communication) to obtain the BF correction value from the mounted interchangeable lens  200 . 
     As illustrated in  FIG. 12 , the C 0  communication is communication performed by sending the command C 0  from the controller  112 . Upon receipt of the command C 0 , the lens controller  201  sends the command C 0 , as data  1 , to the controller  112  of the image pickup apparatus  100 , and then sends data of the BF correction values as data  2  and each subsequent data (data  2  to data X). 
     Subsequently, at step S 610  of  FIG. 6 , the controller  112  sets a BF correction flag. After that, at step S 611 , the controller  112  assigns the BF correction value obtained at step S 609  to the variable BFcomp. Subsequently, at step S 612 , the controller  112  sets a focus detection method (an AF method) to the imaging plane phase difference AF. 
     On the other hand, when the controller  112  determines that the mounted interchangeable lens  200  is not the new-communication compatible lens at step S 604 , the flow proceeds to step S 613  and the controller  112  performs lens communication by a command  80  ( 80  communication) to obtain (receive) a lens ID. 
     As illustrated in  FIG. 12 , the  80  communication is communication performed by sending a command  80  from the controller  112 . Upon receipt of the command  80 , the lens controller  201  sends the command  80 , as data  1 , to the controller  112  of the image pickup apparatus  100  and then sends data indicating an ID and a serial number of the interchangeable lens  200  as data  2  and each subsequent data. More specifically, the value of the data  2  indicates the lens ID, and data  3  and data  4  indicate higher serial numbers and lower serial numbers of the interchangeable lens  200 , respectively. 
     Subsequently, at step S 614 , the controller  112  determines whether or not the mounted interchangeable lens  200  has a large amount of the BF shift.  FIG. 11  is a table relevant to the BF correction (the BF correction related table) stored in the image pickup apparatus  100 . The determination at step S 614  is performed based on the table of relevant to the BF correction in  FIG. 11 . The table of relevant to the BF correction in  FIG. 11  has a data structure including a lens ID, an amount of the BF shift (large or small), presence or absence of a BF correction value, and the BF correction value. The controller  112  refers to the table relevant to the BF correction and determines whether or not the mounted interchangeable lens  200  has a large amount of BF shift based on the lens ID received at step S 613 . 
     The flow proceeds to step S 612  when the controller  112  determines that the mounted interchangeable lens  200  does not have a large amount of BF shift at step S 614 . On the other hand, the flow proceeds to step S 615  when the controller  112  determines that the mounted interchangeable lens  200  has a large amount of BF shift (when the lens ID of the mounted interchangeable lens  200  is either of “01” to “04” in  FIG. 11 ). At step S 615 , the controller  112  determines whether or not the image pickup apparatus  100  has a BF correction value by using the table relevant to the BF correction illustrated in  FIG. 11 . When the image pickup apparatus  100  does not have a BF correction value (when the lens ID of the mounted interchangeable lens  200  is “01” or “02”), the flow proceeds to step S 608  and the controller  112  sets a focus detection method (an AF method) to the contrast AF. 
     On the other hand, the flow proceeds to step S 616  when the image pickup apparatus  100  has a BF correction value (when the lens ID is “03” or “04”). At step S 616 , the controller  112  sets a BF correction flag. Subsequently, at step S 617 , the controller  112  assigns the BF correction value of the table relevant to the BF correction (+60 μm when the lens ID is “03”, or −50 μm when the lens ID is “04”) illustrated in  FIG. 11  to the variable BFcomp. Subsequently, at step S 612 , the controller  112  sets a focus detection method (an AF method) to the imaging plane phase difference AF. After that, the flow proceeds to step S 618  and the controller  112  ends the first selection processing of the AF method. 
     Next, referring to  FIG. 9 , the lens communication performed when the interchangeable lens  200  in this embodiment is the new-communication compatible lens will be described.  FIG. 9  is a flowchart illustrating a procedure of the lens communication in the new-communication compatible lens. Each step of  FIG. 9  is mainly performed based on a command (an instruction) of the lens controller  201  (the lens CPU) of the interchangeable lens  200  (the new-communication compatible lens). 
     First, at step S 901 , the lens controller  201  is on standby until it receives a command from the controller  112  (the camera CPU). When the lens controller  201  receives the command at step S 901 , the flow proceeds to step S 902  and the lens controller  201  determines whether or not the command is the A 0  communication based on the command received as data sent by the image pickup apparatus  100 . The flow proceeds to step S 903  when the command received by the lens controller  201  is A 0  (when the communication is the A 0  communication). On the other hand, the flow proceeds to step S 905  when the lens controller  201  determines that the received command is not A 0 . 
     When the lens controller  201  receives the command A 0  at step S 902 , it sets data indicating whether or not the mounted interchangeable lens  200  is the new-communication compatible lens and then sends the data to the controller  112 . As illustrated in  FIG. 12 , when the mounted interchangeable lens  200  is the new-communication compatible lens, the flow returns to step S 901  after the lens controller  201  sets the data  2  to “01” and sends the data  2  to the controller  112 . 
     When the lens controller  201  receives a command other than the command A 0  at step S 902 , it determines whether or not the communication is the B 0  communication based on the received command at step S 905 . The flow proceeds to step S 906  when the received command is the command B 0  (when the communication is the B 0  communication). On the other hand, the flow proceeds to step S 912  when the received command is not B 0 . 
     When the lens controller  201  receives the command B 0  at step S 905 , it determines whether or not the mounted interchangeable lens  200  has a BF shift at step S 906 . The flow proceeds to step S 907  when the lens controller  201  determines that the mounted interchangeable lens  200  has the BF shift. On the other hand, the flow proceeds to step S 908  when the lens controller  201  determines that the mounted interchangeable lens  200  does not have the BF shift. At step S 907 , the lens controller  201  determines whether or not the mounted interchangeable lens  200  has a BF correction value. The flow proceeds to step S 909  when the lens controller  201  determines that the mounted interchangeable lens  200  has the BF correction value. On the other hand, the flow proceeds to step S 910  when the lens controller  201  determines that the mounted interchangeable lens  200  does not have the BF correction value. Whether or not the mounted interchangeable lens  200  has the BF shift and the BF correction value depends on a lens ID. 
     At steps S 908  to S 910 , the lens controller  201  performs data setting for BF information to be sent to the controller  112  (the camera CPU) and then sends the BF information to the image pickup apparatus  100 . As illustrated in  FIG. 12 , at step S 908 , the lens controller  201  sets data  2  to “00” and sends the data  2  to the controller  112  (the camera CPU), and then the flow returns to step S 901 . At step S 909 , the lens controller  201  sets data  2  to “01” and sends the data  2  to the controller  112 , and then the flow returns to step S 901 . At step S 910 , the lens controller  201  sets data  2  to “02” and then sends the data  2  to the controller  112 , and then the flow returns to step S 901 . 
     When the lens controller  201  receives a command other than the command B 0  at step S 905 , it determines, at step S 912 , whether or not the communication is C 0  communication based on the received command. The flow proceeds to step S 913  when the command received by the lens controller  201  at step S 912  is C 0  (when the communication is C 0  communication). On the other hand, the flow proceeds to step S 918  when the received command is not C 0 . When the lens controller  201  receives other commands (e.g. the command  80 ) according to the definition of each lens communication illustrated in  FIG. 12 , it performs other lens communication processing according to the received command at step S 918 . After that, the flow returns to step S 901 . 
     When the lens controller  201  receives the command C 0  at step S 912 , it determines, at step S 913 , whether or not the mounted interchangeable lens  200  has a BF shift. The flow proceeds to step S 914  when the lens controller  201  determines that the mounted interchangeable lens  200  has the BF shift. On the other hand, the flow proceeds to step S 916  when the lens controller  201  determines that the mounted interchangeable lens  200  does not have the BF shift. At step S 914 , the lens controller  201  determines whether or not the mounted interchangeable lens  200  has a BF correction value. The flow proceeds to step S 915  when the lens controller  201  determines that the mounted interchangeable lens  200  has the BF correction value. On the other hand, the flow proceeds to step S 916  when the lens controller  201  determines that the mounted interchangeable lens  200  does not have the BF correction value. Whether or not the mounted interchangeable lens  200  has the BE shift and the BF correction value depends on the lens ID. 
     At steps S 915  and S 916 , the lens controller  201  performs data setting for the BF correction value to be sent to the controller  112  (the camera CPU) and then sends the BE correction value to the controller  112 . As illustrated in  FIG. 12 , at step S 915 , the lens controller  201  sets the BF correction value to data  2  to data X to be sent to the controller  112  and sends the data  2  to the data X to the controller  112 , and then the flow returns to step S 901 . At step S 916 , the lens controller  201  sets data  2  to be sent to the controller  112  to “00” and sends the data  2  to the controller  112 , and then the flow returns to step S 901 . 
     Next, referring to  FIG. 10 , the lens communication performed when the interchangeable lens  200  in this embodiment is the new-communication incompatible lens will be described.  FIG. 10  is a flowchart illustrating a procedure of the lens communication in the new-communication incompatible lens. Each step of  FIG. 10  is mainly performed based on a command of the lens controller  201  (the lens CPU) of the interchangeable lens  200  (the new-communication incompatible lens). 
     First, at step S 1001 , the lens controller  201  is on standby until it receives a command from the controller  112  (the camera CPU). When the lens controller  201  receives the command at step S 1001 , the flow proceeds to step S 1002  and the lens controller  201  determines whether or not the command is the A 0  communication based on the command received as data sent by the image pickup apparatus  100 . The flow proceeds to step S 1003  when the command received by the lens controller  201  is A 0  (when the communication is the A 0  communication). On the other hand, the flow proceeds to step S 1005  when the lens controller  201  determines that the received command is not A 0 . 
     When the lens controller  201  receives the command A 0  at step S 1002 , it sets data indicating whether or not the mounted interchangeable lens  200  is the new-communication incompatible lens and then sends the data to the controller  112  at step S 1003 . As illustrated in  FIG. 12 , when the mounted interchangeable lens  200  is the new-communication incompatible lens, the lens controller  201  sets the data  2  to “00” and sends the data  2  to the controller  112 , and then the flow returns to step S 1001 . When the lens controller  201  receives other commands (e.g. the command  80 ) according to the definition of each lens communication illustrated in  FIG. 12 , it performs other lens communication processing according to the received command at step S 1005 , and then the flow returns to step S 1001 . 
     As described above, in this embodiment, the controller  112  performs the lens communication by the command A 0  (the A 0  communication) to determine (identify) whether or not the mounted interchangeable lens  200  is the new-communication compatible lens (step S 603  of  FIG. 6 ). When the new-communication compatible lens is mounted (“YES” at step S 604 ), the controller  112  obtains BF information from the new-communication compatible lens (step S 605 ). That is, the controller  112  receives focus information from the interchangeable lens  200 . 
     When the mounted interchangeable lens  200  does not have the BF shift (“YES” at step S 606 ), the controller  112  sets an AF method to the imaging plane phase difference AF (step S 612 ). That is, the controller  112  selects the second focus detection unit (the imaging plane phase difference AF) to perform the focus control when the focus information received from the interchangeable lens  200  is information indicating that the mounted interchangeable lens  200  does not have the focus shift. 
     On the other hand, when the interchangeable lens  200  has the BF shift (“NO” at step S 606 ) and has the BF correction value (“YES” at step S 607 ), the controller  112  obtains the BF correction value (step S 609 ) from the mounted interchangeable lens  200 . Then, the controller  112  sets an AF method to the imaging plane phase difference AF (step S 612 ). That is, when the focus information received from the interchangeable lens  200  is information indicating that the interchangeable lens  200  has the focus shift and has the focus correction value to correct the focus shift, the controller  112  selects the second focus detection unit. Then, the controller  112  performs the focus control by using the focus correction value received from the interchangeable lens  200 . 
     When the interchangeable lens  200  has the BF shift and does not have the BF correction value (“NO” at step S 607 ), the controller  112  sets an AF method to the contrast AF (step S 608 ). That is, when the focus information received from the interchangeable lens  200  is information indicating that the interchangeable lens  200  has the focus shift and does not have the focus correction value to correct the focus shift, the controller  112  selects the first focus detection unit to perform the focus control. 
     When the interchangeable lens  200  is the new-communication incompatible lens (“NO” at step S 604 ), the controller  112  performs the lens communication by the command  80  (the  80  communication) to obtain a lens ID (step S 613 ). That is, the controller  112  specifies the focus information based on the lens ID received from the interchangeable lens  200 . 
     When the controller  112  determines, with reference to the table relevant to the BF correction ( FIG. 11 ) stored in the image pickup apparatus  100 , that the interchangeable lens  200  does not have a large amount of focus shift (“NO” at step S 614 ), the controller  112  sets an AF method to the imaging plane phase difference AF (step S 612 ). That is, when the controller  112  determines that the interchangeable lens  200  does not have a large amount of focus shift (the interchangeable lens  200  has a focus shift less than a predetermined value) based on the lens ID received from the interchangeable lens  200 , it selects the second focus detection unit to perform the focus control. 
     On the other hand, when the interchangeable lens  200  has a large amount of BF shift (“YES” at step S 606 ) and has the BF correction value stored in the image pickup apparatus  100  (“YES” at step S 615 ), the controller  112  obtains the BF correction value from the table relevant to the BF correction stored in the image pickup apparatus  100  (steps S 616  and S 617 ). After that, the controller  112  sets an AF method to the imaging plane phase difference AF (step S 612 ). That is, when the focus information specified based on the lens ID is information indicating that the interchangeable lens  200  has a large amount of focus shift (the interchangeable lens  200  has a focus shift not less than the predetermined value) and has a focus correction value, the controller  112  selects the second focus detection unit. Then, the controller  112  performs the focus control by using the focus correction value received from the interchangeable lens  200 . 
     On the other hand, when the interchangeable lens  200  does not have the BF correction value stored in the image pickup apparatus  100  (“NO” at step S 615 ), the controller  112  sets an AF method to the contrast AF (step S 608 ). That is, when the focus information specified based on the lens ID is information indicating that the interchangeable lens  200  has a large amount of focus shift and does not have a focus correction value, the controller  112  selects the first focus detection unit to perform the focus control. 
     The configuration of this embodiment makes it possible, with respect to a conventional interchangeable lens, i.e. a new-communication incompatible lens, to appropriately select the imaging plane phase difference AF or the contrast AF to be performed along with the BF correction by storing the table relevant to the BF correction in the image pickup apparatus  100 . On the other hand, the configuration of this embodiment makes it possible, with respect to a new interchangeable lens, i.e. a new-communication compatible lens, to select an appropriate focus detection method by obtaining focus information from the lens. Accordingly, an appropriate focus detection can be performed in which an influence of a focus shift caused by an aberration is suppressed depending on a mounted interchangeable lens. 
     Second Embodiment 
     Next, referring to  FIGS. 7 and 8 , the second embodiment of the present invention will be described. This embodiment relates to second selection processing of an AF method in which a user can register a focus correction value, which is performed instead of the first selection processing of the AF method performed at step S 302  of  FIG. 3 . 
       FIG. 7  is a flowchart illustrating a procedure of the second selection processing of the AF method in this embodiment. Each step of  FIG. 7  is mainly performed based on a command (an instruction) of the controller  112  (the camera CPU).  FIG. 7  is different from the flowchart of  FIG. 6  (the first embodiment) in that steps S 703 , S 719 , and S 720  are added. Since the steps S 701 , S 702 , S 704  to S 718 , and S 721  are the same as steps S 601  to S 618  of  FIG. 6  respectively, the description thereof will be omitted. 
     Subsequently to step S 702 , at step S 703 , the controller  112  (a registration unit) determines whether or not a focus correction value is registered. The flow proceeds to step S 719  when the controller  112  determines that the focus correction value is registered. On the other hand, the flow proceeds to step S 704  when the controller  112  determines that the focus correction value is not registered. The registration of a focus correction value will be described later. 
     The controller  112  sets a BF correction flag at step S 719  when it determines, at step S 703 , that the focus correction value is registered. Subsequently, at step S 720 , the controller  112  assigns the registered focus correction value to the variable BFcomp. After that, the flow proceeds to step S 713  and the controller  112  sets an AF method to the imaging plane phase difference AF. 
     Next, referring to  FIG. 8 , the registration of a focus correction value in this embodiment will be described.  FIG. 8  is a flowchart illustrating a procedure of registration processing of the focus correction value. Each step of  FIG. 8  is mainly performed based on a command (an instruction) of the controller  112  (the camera CPU). In this embodiment, a BF correction value can be registered for each lens by using lens IDs and serial numbers. In this embodiment, the maximum registration number of BF correction values is, for example, 50. 
     First, at step S 801 , the controller  112  performs the lens communication by the command  80  (the  80  communication) as illustrated in  FIG. 12  to obtain a lens ID. In the command  80 , the value of data  2  received by the image pickup apparatus  100  indicates the lens ID, and the values of data  3  and data  4  indicate a higher serial number and a lower serial number, respectively. Subsequently, at step S 802 , the controller  112  is on standby until a start button (not illustrated in the drawing) is pressed. 
     When the start button is pressed at step S 802 , the flow proceeds to step S 803  and a focus correction value (the BF correction value) is input via an operating member (not illustrated in the drawing). In this embodiment, the focus correction value can be input by the micrometer within a range of ±50 μm. 
     Subsequently, at step S 804 , the controller  112  determines the status of an end button (not illustrated in the drawing). The controller  112  continues step S 804  until the end button is pressed and then the flow proceeds to step S 805 . At step S 805 , the controller  112  determines the focus correction value (the BF correction value) input at step S 803 . The flow proceeds to step S 807  when the focus correction value is 0 (zero). At step S 807 , the controller  112  clears the BF correction value registered for each lens. 
     On the other hand, the flow proceeds to step S 806  when the focus correction value is not 0 (zero). At step S 806 , the controller  112  registers a focus correction value (a BF correction value) for each lens. After that, the flow proceeds to step S 808  and the controller  112  ends the registration processing of the focus correction value. 
     As described above, in this embodiment, when a focus correction value (a BF correction value) is registered (“YES” at step S 703 ), the controller  112  sets an AF method to the imaging plane phase difference AF by using the registered BF correction value (steps S 719  and S 720 ). That is, the image pickup apparatus  100  of this embodiment further includes a registration unit configured to register a focus correction value to correct a focus shift of the interchangeable lens  200 . The controller  112  selects the second focus detection unit and then performs the focus control by using the focus correction value registered in the registration unit. On the other hand, the controller  112  performs the same processing as that in the first embodiment when the BF correction value is not registered (“NO” at step S 703 ). 
     Moreover, in order to identify whether or not the mounted interchangeable lens  200  is the new-communication compatible lens, the controller  112  performs the lens communication by the command A 0  (step S 703  of  FIG. 7 ). The controller  112  obtains the BF information from the interchangeable lens  200  (step S 706 ) when the mounted interchangeable lens  200  is the new-communication compatible lens (“YES” at step S 705 ). In addition, the controller  112  sets an AF method to the imaging plane phase difference AF (step S 713 ) when the mounted interchangeable lens  200  does not have the BF shift (“YES” at step S 707 ). 
     When the interchangeable lens  200  has the BF shift (“NO” at step S 707 ) and has the BF correction value (“YES” at step S 708 ), the controller  112  obtains the BF correction value from the interchangeable lens  200  (step S 710 ) and then sets an AF method to the imaging plane phase difference AF (step S 713 ). When the interchangeable lens  200  does not have the BF correction value (“NO” at step S 708 ), the controller  112  sets an AF method to the contrast AF (step S 709 ). 
     When the interchangeable lens  200  is the new-communication incompatible lens (“NO” at step S 705 ), the controller  112  performs the lens communication by the command  80  to obtain a lens ID (step S 714 ). 
     When the controller  112  determines, with reference to the table relevant to the BF correction ( FIG. 11 ) stored in the image pickup apparatus  100  (the controller  112 ), that the interchangeable lens  200  does not have a large amount of focus shift (“NO” at step S 715 ), the controller  112  sets an AF method to the imaging plane phase difference AF (step S 713 ). When the interchangeable lens  200  has the large amount of focus shift (“YES” at step S 715 ) and the BF correction value is stored in the image pickup apparatus  100  (“YES” at step S 716 ), the controller  112  obtains the BF correction value from the table relevant to the BF correction stored in the image pickup apparatus  100  (steps S 717  and S 718 ). Then, the controller  112  sets an AF method to the imaging plane phase difference AF (step S 713 ). On the other hand, the BF correction value for the interchangeable lens  200  is not stored in the image pickup apparatus  100  (“NO” at step S 716 ), the controller  112  sets an AF method to the contrast AF (step S 709 ). Accordingly, also in this embodiment, an appropriate focus detection can be performed in which an influence of a focus shift caused by an aberration is suppressed depending on a mounted interchangeable lens. 
     Other Embodiments 
     Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment(s) of the present invention, 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 embodiments. The computer may comprise one or more of a central processing unit (CPU), micro processing unit (MPU), or other circuitry, and may include a network of separate computers or separate computer processors. 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. 2013-079723, filed on Apr. 5, 2013, which is hereby incorporated by reference herein in its entirety.