Patent Publication Number: US-11656537-B2

Title: Lens apparatus and image pickup system

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a lens apparatus attachable to and detachable from an image pickup apparatus. 
     Description of the Related Art 
     In an interchangeable lens type camera system, an old type interchangeable lens and a new type interchangeable lens may be detachably attached to the camera. Thus, the camera is required to be compatible with the specification of any type of the interchangeable lens. 
     Japanese Patent Laid-Open No. 2012-128203 discloses a camera that switches a communication method according to the type of the attached interchangeable lens when the old type interchangeable lens and the new type interchangeable lens support different communication methods. 
     An interchangeable lens for a mirrorless camera has recently been proposed, which has a backfocus shorter than that of the conventional interchangeable lens. The shortened backfocus improves the design freedom for the overall lens length more effectively than an optical system having a long backfocus, and consequently enables various aberrations to be easily corrected. There is also proposed a camera system etc. that provides an old type communication method to an interchangeable lens having a long backfocus and a new type communication method to an interchangeable lens having a short backfocus. 
     However, the interchangeable lenses for mirrorless cameras do not always need the new type communication method. For example, macro lenses or ultrawide-angle lenses do not require the autofocus (AF) speed or the followability to a dynamic object more frequently than telephoto lenses for sports photography, and thus do not require a higher communication speed of the new type communication method (higher communication performance). In addition, since a semiconductor chip equipped with a high-performance CPU compatible with the new type communication method is likely to have a footprint larger than that of a semiconductor chip equipped with a CPU compatible with the old type communication method, a design freedom of an optical system (degree of freedom of the optical design) may be narrowed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a lens apparatus and an image pickup system, each of which can improve both an optical design freedom and a communication performance. 
     A lens apparatus attachable to and detachable from an image pickup apparatus includes an imaging optical system, a first-shaped mount part engageable with a mount part of the image pickup apparatus, and a communicator communicable with the image pickup apparatus. Any one of a plurality of lens apparatuses including a first lens apparatus and a second lens apparatus is attachable to and detachable from the image pickup apparatus directly or via an intermediate adapter. The first lens apparatus includes a mount part engageable with the mount part of the image pickup apparatus, and is communicable with the image pickup apparatus using a first communication method. The second lens apparatus includes a second-shaped mount part that is not engageable with the mount part of the image pickup apparatus, and the second lens apparatus is attachable to the image pickup apparatus via the intermediate adapter, and is communicable with the image pickup apparatus using a second communication method different from the first communication method. The communicator is communicable with the image pickup apparatus using the second communication method, and uncommunicable with the image pickup apparatus using the first communication method. 
     An image pickup system including the above lens apparatus also constitutes another aspect of the present invention. 
     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    explains a camera system according to this embodiment. 
         FIGS.  2 A to  2 D  illustrate a structure of a mount part according to this embodiment. 
         FIG.  3    illustrates circuit configurations of a camera and a first lens apparatus according to this embodiment. 
         FIG.  4    illustrates circuit configurations of the camera, an intermediate adapter, and a second lens apparatus according to this embodiment. 
         FIG.  5    illustrates circuit configurations of the camera and a third lens apparatus according to this embodiment. 
         FIGS.  6 A to  6 E  schematically illustrate peripheral circuits of a TYPE terminal according to this embodiment. 
         FIGS.  7 A to  7 C  explain an asynchronous communication according to this embodiment. 
         FIG.  8    explains a clock synchronous communication according to this embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the accompanying drawings, a detailed description will be given of embodiments according to the present invention. 
     Before an embodiment according to the present invention is described, terms used in this specification will be described. In this specification, the mount part (or unit) is a connector provided to each of a camera (image pickup apparatus), an intermediate adapter, and an interchangeable lens (lens apparatus). Each mount part has a plurality of electrical contacts, and when the intermediate adapter or the interchangeable lens is attached to (or mounted on) the camera, the electrical contacts provided on the mount parts contact each other. In other words, the mount part has not only a function of mechanically connecting the camera and the adapter or the interchangeable lens to each other, but also a function of electrically connecting them to each other. 
     A backfocus refers to an air conversion length from a lens surface closest to the image plane of the imaging optical system to the image plane. A flange back refers to a distance from a mount reference surface of the mount part of the camera to an imaging plane of an image sensor (image pickup element) built in the camera. In other words, the flange back is a distance from the mount reference plane of the mount part on the interchangeable lens to the image plane. 
     Referring now to the accompanying drawings, a detailed description will be given of an interchangeable lens according to this embodiment. In each figure, the same components are designated by the same reference numerals, and a duplicate description thereof will be omitted. 
     Camera System 
     Referring now to  FIG.  1   , a description will be given of a camera system according to this embodiment.  FIG.  1    is an explanatory diagram of a camera system (image pickup system)  10 , and illustrates a mutual relationship among a camera (image pickup apparatus)  100 , interchangeable lenses (lens apparatuses)  200 ,  300 , and  600 , and intermediate adapters  400  and  500 . The apparatuses indicated by arrows in  FIG.  1    indicate that the mount parts of the apparatuses are connectable and attachable. The interchangeable lenses  200  and  600  are directly attachable to and detachable from the camera  100 . The interchangeable lens  300  is indirectly attachable to and detachable from the camera  100  via the intermediate adapter  400 . As described above, the camera system  10  includes at least the camera  100  and one of the interchangeable lenses  200 ,  300 , and  600 . The camera system  10  may include accessories such as the intermediate adapters  400  and  500 . 
     The camera  100  has an image sensor  180  such as a CMOS sensor. The image sensor  180  photoelectrically converts an object image (optical image) formed by an imaging optical system in the interchangeable lens (such as any of the interchangeable lenses  200 ,  300 , and  600 ) mounted on the camera  100 , and outputs an electric signal (image data). 
     The interchangeable lens (first lens apparatus)  200  has an imaging optical system  280  that forms an object image, and is attachable to the camera  100  directly or via the intermediate adapter  500 . Here, a mount part  250  of the interchangeable lens  200  and a mount part  550   a  of the intermediate adapter  500  are each serves as a first-shaped mount part engageable with the mount part  150  of the camera  100 . A mount part  550   b  of the intermediate adapter  500  has the same shape as the mount part  150 . 
     The interchangeable lens (second lens apparatus)  300  has an imaging optical system  380  that forms an object image, and is not directly attachable to the camera  100 . A mount part  350  of the interchangeable lens  300  is a second-shaped mount part that is not engageable with the mount part  150  of the camera  100 . Therefore, the interchangeable lens  300  is attached to the camera  100  via the intermediate adapter  400  having a mount  450   a  engageable with the mount part  150  and the mount  450   b  engageable with the mount  350 . 
     The interchangeable lens (third lens apparatus)  600  has an imaging optical system  680  that forms an object image, and is attachable to the camera  100  directly or via the intermediate adapter  500 . A mount part  650  of the interchangeable lens  600  is also a first-shaped mount part that is engageable with the mount part  150  of the camera  100 . 
     The camera  100  according to this embodiment is a so-called mirrorless type camera in which a quick return mirror or a half mirror is not disposed on the optical path. The imaging optical systems  280  and  680  are so-called short-back optical systems designed for the camera  100 . The imaging optical system  380  may be an optical system designed for the camera in which a mirror is disposed on the optical path. A backfocus d1 [mm] (backfocus at the wide-angle end when the imaging optical system  280  is a zoom lens) and a flange back d2 [mm] of the imaging optical system  680  may satisfy at least one of the following conditional expressions (1) and (2):
 
10≤d1≤30  (1)
 
14≤d2≤22  (2)
 
     Satisfying at least one of the conditional expressions (1) and (2) can improve the optical design freedom of each of the imaging optical systems  280  and  680 , and provide an imaging optical system in which various aberrations are satisfactorily corrected. 
     Structure of Mount Part 
     Referring now to  FIGS.  2 A to  2 D , a description will be given of a structure of the mount parts  150 ,  250 ,  450   b , and  350 .  FIGS.  2 A to  2 D  are structural diagrams of the mount parts  150 ,  250 ,  450   b , and  350 , respectively.  FIG.  2 A  illustrates the mount part  150  on the camera  100  viewed from the object side.  FIG.  2 B  illustrates the mount part  250  on the interchangeable lens  200  viewed from the image side.  FIG.  2 C  illustrates the mount part  450   b  on the intermediate adapter  400  viewed from the object side.  FIG.  2 D  illustrates the mount part  350  on the interchangeable lens  300  viewed from the image side. 
     The mount part  150  illustrated in  FIG.  2 A  includes a ring-shaped mount reference surface  151  for ensuring a predetermined flange back. Bayonet claws  152   a ,  152   b ,  152   c  are provided inside the mount reference surface  151  at three locations in the circumferential direction. The mount part  150  has a positioning lock pin  153  in bayonetting the opposite mount parts ( 250 ,  450   a ,  550   a , and  650 ) onto the mount part  150  so that the lock pin  153  can project and draw from the mount reference surface  151 . When the mount part  150  and the mount part of the intermediate adapter  500  or the interchangeable lenses  200  and  600  relatively rotate up to the mounting completion positions, the engagement holes provided in these mount parts engage with the lock pin  153 . 
     A camera-side contact holder  154  is provided in the area inside the bayonet claws  152   a ,  152   b , and  152   c . The camera-side contact holder  154  holds electrical contacts (camera-side electrical contacts)  1001  to  1012 . The mount part  550   b  has the same structure as the mount part  150  illustrated in  FIG.  2 A . 
     The mount part  250  illustrated in  FIG.  2 B  has a ring-shaped mount reference surface  251  which is a reference surface of the flange back. Bayonet claws  252   a ,  252   b , and  252   c  are provided inside the mount reference surface  251  at three locations in the circumferential direction. The mount part  250  has an engagement hole  253 . The engagement hole  253  is engaged with the lock pin  153  when the mounting of the interchangeable lens  200  on the camera  100  is completed. A contact holder  254  is provided in an area inside the bayonet claws  252   a ,  252   b , and  252   c.  The contact holder  254  holds the electrical contacts  2001  to  2012 . Each of the mount parts  450   a ,  550   a , and  650  has the same structure as that of the mount part  250  illustrated in  FIG.  2 B . 
     The mount part  450   b  illustrated in  FIG.  2 C  has a mount reference surface  451 , bayonet claws  452   a ,  452   b , and  452   c , and a contact holder  454 , similar to the mount part  150 . However, the lengths of the bayonet claws  452   a ,  452   b , and  452   c  and the intervals between the bayonet claws are different from those of the bayonet claws  152   a ,  152   b , and  152   c  in the mount part  150 . 
     The mount part  350  illustrated in  FIG.  2 D  has a mount reference surface  351 , bayonet claws  352   a ,  352   b , and  352   c , and a contact holder  354 , similar to the mount part  250 . However, the lengths of the bayonet claws  352   a ,  352   b , and  352   c  and the intervals between the adjacent bayonet claws are different from those of the bayonet claws  252   a ,  252   b , and  252   c  of the mount part  250 . Each electrical contact illustrated in  FIGS.  2 A to  2 D  may have either a pin shape or a contact piece as long as it can carry electricity. 
     Circuit Configuration 
     Referring now to  FIG.  3   , a description will be given of the interchangeable lens  200  that is attached to the camera  100 .  FIG.  3    is a circuit configuration diagram of the camera  100  and the interchangeable lens (first lens apparatus)  200 , and illustrates the interchangeable lens  200  that is connected to the camera  100 . The interchangeable lens  200  and the camera  100  can communicate with each other via a communication path formed by a part of a plurality of electrical contacts provided on the mount parts  150  and  250 . The interchangeable lens  200  and the camera  100  can perform a first communication, a second communication, and a third communication, which will be described later. The first communication is performed by a clock synchronous communication (second communication method) or an asynchronous communication (first communication method). 
     A camera controller (communicator)  101  controls an output of the electrical contact provided to the mount part  150 , and processes a signal input to the electrical contact, thereby controlling communications between the interchangeable lenses  200 ,  400 ,  600 , etc. mounted on the camera  100  and the camera  100 . A camera power supply unit  103  is a power supply used to operate each component in the camera  100 , and an interchangeable lens and an intermediate adapter attached to the camera  100 . The camera power supply unit  103  can generate a plurality of different voltages, and supplies power of each voltage to each component in the camera  100 , the interchangeable lens and the intermediate adapter attached to the camera  100 . A power supply switching unit  104  supplies power to a first communication I/F (interface) unit  102   a . The power supply switching unit  104  is supplied with two power supplies having different voltage values from the power supply unit  103 , and switches the power supply to the first communication I/F (interface) unit  102   a  under the control of the camera controller  101 . 
     A lens controller  201  controls an output of an electrical contact provided to the mount part  250  and processes a signal input to the electrical contact, thereby controlling communications between the camera  100  and the interchangeable lens  200 . A lens power supply unit  203  generates a power supply of a predetermined voltage from the power supply supplied from the camera  100  and supplies the power supply to the lens controller  201  and a lens-side communication I/F unit  202 . 
     The electrical contacts  1001  and  2001  are terminals used to supply power (control power) mainly used for communications performed between the camera  100  and the interchangeable lens  200  and other control calculations, from the power supply unit  103  of the camera  100  to the interchangeable lens  200 . The electrical contacts  1001  and  2001  will also be referred to as VDD terminals  1001  and  2001  hereinafter. In this embodiment, the voltage (VDD voltage) of power supplied to the interchangeable lens  200  by the VDD terminal  1001  is 5.0V. 
     The electrical contacts  1002  and  2002  are terminals mainly used to supply power (driving power) used for the operation of a driving system (driving circuit unit  204 ) such as a motor, from the camera  100  to the interchangeable lens  200 . The electrical contacts  1002  and  2002  will also be referred to as VBAT terminals  1002  and  2002  hereinafter. In this embodiment, the voltage of power supplied to the interchangeable lens  200  by the VBAT terminal  1002  is 4.5V. The VDD terminal and the VBAT terminal are collectively referred to as a power supply system terminal. 
     The electrical contacts  1012  and  2012  are terminals for grounding the communication control system circuits of the camera  100  and the interchangeable lens  200  or ground terminals corresponding to the VDD terminal. The electrical contacts  1012  and  2012  will also be referred to as DGND terminals  1012  and  2012  hereinafter. 
     The electrical contacts  1004  and  2004  are terminals for grounding a driving system circuit including a motor and the like provided to the camera  100  and the interchangeable lens  200  or ground terminals corresponding to the VBAT terminal. The electrical contacts  1004  and  2004  will also be referred to as PGND terminals  1004  and  2004  hereinafter. The DGND terminal and the PGND terminal will be collectively referred to as a ground terminal. 
     The electrical contacts  1005  and  2005  are terminals for detecting that the interchangeable lens  200  is attached to the camera  100 . The camera controller  101  detects an attachment and a detachment of the interchangeable lens  200  to and from the camera  100  based on the voltage level of the electrical contact  1005 . When the camera controller  101  detects the attachment of the interchangeable lens, the power supply to the interchangeable lens  200  is started via the VDD terminal  1001  and the VBAT terminal  1002 . The electrical contacts  1005  and  2005  will also be referred to as MIF terminals  1005  and  2005  hereinafter. 
     The electrical contact (first electrical contact)  1003  and the electrical contact  2003  are terminals for enabling the type of the interchangeable lens directly or indirectly attached to the camera  100  via an intermediate adapter, to be determined. The electrical contacts  1003  and  2003  will also be referred to as TYPE terminals. A method for determining the type will be described later. 
     The electrical contacts  1006  to  1008  and  2006  to  2008  are terminals used for the first communication. The first communication is a communication performed between the camera  100  and the interchangeable lens  200 , and transmits/receives ID information (individual information) of the interchangeable lens  200 , information necessary for image capturing, control instructions, and the like. The electrical contacts  2006  and  2008  are pulled up to 3.0 V in the interchangeable lens  200 . The electrical contacts  1007  and  1008  are pulled up to 3.0V in the camera  100 . Thereby, the communication voltage of the first communication becomes 3.0V (first voltage). 
     The electrical contacts  1009  and  2009  are terminals used for the second communication. The second communication is a communication for unidirectionally transmitting data from the interchangeable lens  200  to the camera  100 . The communication voltage of the second communication is 3.0 V, which is the same as the driving voltage of the lens-side communication I/F unit  202 . 
     The electrical contacts  1010 ,  1011 ,  2010 , and  2011  are terminals used for the third communication. The third communication is a communication performed between the camera  100  and the interchangeable lens  200 , and a communication mutually performed among the camera  100 , the interchangeable lens  200 , and the intermediate adapter  500 , when the intermediate adapter  500  is connected. The electrical contacts  1010  and  1011  are pulled up in the camera  100 . Thereby, the communication voltage of the third communication is 3.0V. 
     Referring now to  FIG.  4   , a description will be given of the interchangeable lens  300  that is attached to the camera  100  via the intermediate adapter  400 .  FIG.  4    is a circuit configuration diagram of the camera  100 , the intermediate adapter  400 , and the interchangeable lens (second lens apparatus)  300 , and illustrates the interchangeable lens  300  that is attached to the camera  100  via the intermediate adapter  400 . 
     The interchangeable lens  300  cannot perform the second communication or the third communication with the camera  100 , but can perform the first communication. The first communication is performed by the clock synchronous communication. The intermediate adapter  400  has an adapter controller  401  that communicates with the camera  100  and performs processing according to the operation of an unillustrated operation member. The operation of the operation member is transmitted to the adapter controller  401  via an operation input unit  402 . 
     The mount part  450   a  is similar to the mount part  250  of the interchangeable lens  200  described above. However, the internal circuit of the intermediate adapter  400  and that of the interchangeable lens  200  are different from each other. More specifically, the DCL terminal  2006 , the DLC terminal  2007 , and the LCLK terminal  2008  used for the first communication are not connected to the adapter controller  401  in the intermediate adapter  400 , and are through-wired to the corresponding electrical contacts of the mount part  450   b . On the other hand, the DCA terminal  2010  and the CS terminal  2011  used for the third communication are connected to the adapter controller  401  in the intermediate adapter  400 . 
     The DLC2 terminal  2009  used for the second communication is pulled down to the same level as the DGND terminal  2012  via a resistor in the intermediate adapter  400 . This is because the interchangeable lens  300  and the camera  100  perform no second communication. 
     The TYPE terminal  2003  is pulled down to the same level as the DGND terminal  2012  via a resistor  422  in the intermediate adapter  400 . The resistor  422  has a resistance value different from that of a resistor  222  in the interchangeable lens  200 . Thereby, the voltage of the electrical contact (TYPE terminal)  1003  can be made different between when the interchangeable lens  300  is attached to the camera  100  via the intermediate adapter  400  and when the interchangeable lens  200  is attached. 
     Next follows a description of the electrical contacts provided to the mount parts  450   b  and  350 . The electrical contacts  3001  and  4001  are terminals used to supply power (driving power) used for the operation of a driving system (driving circuit unit  304 ) such as a motor, from the VBAT terminal  1002  of the camera  100  to the interchangeable lens  300 . In the intermediate adapter  400 , the VBAT terminal  2002  is through-wired to the electrical contact  4001 . The electrical contacts  3001  and  4001  will also be referred to as VBAT terminals  3001  and  4001  hereinafter. In this embodiment, the voltage of power supplied to the interchangeable lens  300  by the VBAT terminal  1002  is 4.5V. 
     The electrical contacts  3004  and  4004  are terminals used to supply control power from the VDD terminal  1001  of the camera  100  to the interchangeable lens  300 . In the intermediate adapter  400 , the VDD terminal  2001  is through-wired to the electrical contact  4004  and is also connected to an adapter power supply unit  403  in the intermediate adapter  400 . The adapter power supply unit  403  generates a 3.0 V power supply as the power supply to the adapter controller  401  and the operation input unit  402 . The electrical contacts  3004  and  4004  will also be referred to as VDD terminals  3004  and  4004  hereinafter. In this embodiment, the voltage of power supplied to the interchangeable lens  300  by the VDD terminal  1001  is 5.0V. 
     The electrical contacts  3003  and  4003  are terminals for grounding the driving systems of the camera  100  and the interchangeable lens  300  or ground terminals corresponding to the VBAT terminal. In the intermediate adapter  400 , the PGND terminal  2004  is through-wired to the electrical contact  4003 . The electrical contacts  3003  and  4003  will also be referred to as the PGND terminals  3003  and  4003  hereinafter. 
     The electrical contacts  3008  and  4008  are terminals for grounding the communication control systems in the camera  100  and the interchangeable lens  300  or ground terminals corresponding to the VDD terminal. In the intermediate adapter  400 , the DNG terminal  2012  is through-wired to the electrical contact  4008 . The electrical contacts  3008  and  4008  will also be referred to as DGND terminals  3008  and  4008  hereinafter. 
     The electrical contacts  3002  and  4002  are terminals used to detect that the interchangeable lens  300  is attached to the camera  100  via the intermediate adapter  400 . When detecting attachment of the interchangeable lens  300 , the camera controller  101  starts supplying power to the interchangeable lens  300 . In the intermediate adapter  400 , the MIF terminal  2005  is through-wired to the electrical contact  4002 . The electrical contacts  3002  and  4002  will also be referred to as the MIF terminals  3002  and  4002  hereinafter. 
     The electrical contacts  3005  to  3007  and  4005  to  4007  are terminals used for the first communication described later. Inputs and outputs of the electrical contacts  3005  to  3007  are controlled by a lens controller  301  via a lens-side communication I/F unit  302 . The electrical contacts  3005 ,  3006 , and  3007  will also be referred to as a DCL terminal  3005 , a DLC terminal  3006 , and an LCLK terminal  3007  hereinafter. The electrical contacts  4005 ,  4006 , and  4007  will also be referred to as a DCL terminal  4005 , a DLC terminal  4006 , and an LCLK terminal  4007  hereinafter. 
     When the interchangeable lens  300  is attached via the intermediate adapter  400 , the interface voltages of the first communication I/F unit  102   a  and the lens-side communication I/F unit  302  are set to the same voltage supplied from the VDD terminal as 5.0V (second voltage). The second voltage is a voltage different from the first voltage. 
     On the other hand, the interface voltage of the second/third communication I/F unit  102   b  is set to 3.0V. In other words, when the interchangeable lens  300  is attached to the camera  100  via the intermediate adapter  400 , the communication voltage for the first communication and that for the third communication are different from each other. As described later, when the interchangeable lens  300  is attached to the camera  100  via the intermediate adapter  400 , no second communication is performed. 
     Referring now to  FIG.  5   , a description will be given of the interchangeable lens  600  that is directly attached to the camera  100 .  FIG.  5    is a circuit configuration diagram of the camera  100  and the interchangeable lens (third lens apparatus)  600 , and illustrates the interchangeable lens  600  connected to the camera  100 . The interchangeable lens  600  cannot perform the second communication or the third communication with the camera  100 , but can perform the first communication. The first communication is performed using the clock synchronous communication. 
     The mount part  650  has the same shape as the mount part  250 , and the arrangement of the electrical contacts  6001  to  6012  provided to the mount part  650  is the same as that of the electrical contacts  2001  to  2012  in the interchangeable lens  200 . A lens controller  601  as the communicator controls an output of the electrical contact provided to the mount part  650  and processes a signal input to the electrical contact, thereby controlling communications between the camera  100  and the interchangeable lens  600 . 
     A lens power supply unit  603  generates a power supply having a predetermined voltage from the power supply supplied from the camera  100  and supplies power supply to the lens controller  601  and a lens-side communication I/F unit  602 . The electrical contact  6001  is a terminal used to supply power (control power) used for communications performed between the camera  100  and the interchangeable lens  600  and other control calculations, from the power supply unit  103  of the camera  100  to the interchangeable lens  600 . The electrical contact  6001  will also be referred to as a VDD terminal  6001  hereinafter. In this embodiment, the voltage (VDD voltage) of power supplied to the interchangeable lens  600  by the VDD terminal  6001  is 5.0V. 
     The power (driving power) used for operating a driving system (driving circuit unit  604 ) such as a motor is supplied from the camera  100  via the electrical contact  6002 . The electrical contact  6002  will also be referred to as a VBAT terminal  6002  hereinafter. In this embodiment, the voltage of power supplied to the interchangeable lens  600  by the VBAT terminal  6002  is 4.5V. The VDD terminal and the VBAT terminal will be collectively referred to as a power supply system terminal. 
     The electrical contact  6012  is a terminal that grounds the communication control system circuit in the interchangeable lens  600  or a ground terminal corresponding to the VDD terminal. The electrical contact  6012  will also be referred to as a DGND terminal  6012  hereinafter. 
     The electrical contact  6004  is a terminal for grounding a driving system circuit such as a motor installed on the interchangeable lens  600 , or a ground terminal corresponding to the VBAT terminal. The electrical contact  6004  will also be referred to as a PGND terminal  6004  hereinafter. The DGND terminal and the PGND terminal will be collectively referred to as a ground terminal. 
     The electrical contact  6005  is a terminal for detecting that the interchangeable lens  200  is attached to the camera  100 . The camera controller  101  detects an attachment and a detachment of the interchangeable lens  600  to and from the camera  100  according to the voltage level of the electrical contact  1005 . The electrical contact  6005  will also be referred to as an MIF terminal  6005  hereinafter. 
     The electrical contact (predetermined electrical contact)  6003  is a terminal (TYPE terminal) used to determine the type of the interchangeable lens attached to the camera  100  directly or via the intermediate adapter. The electrical contact  6003  is pulled down to the same level as the DGND terminal  6012  via a resistor  622  in the interchangeable lens  600 . In other words, the electrical contact  6003  is not used for the power supply from the camera  100  or for communication with the camera  100 , and is connected to the ground via the resistor  622 . 
     The resistance value of the resistor  622  is different from that of the resistor  222  of the interchangeable lens  200 . The resistance value of the resistor  622  may be closer to that of the resistor  422  than that of the resistor  222 . In this embodiment, the resistance value of the resistor  622  is the same as that of the resistor  422 . Thereby, the voltage of the electrical contact (TYPE terminal)  1003  can be made different between when the interchangeable lens  600  is attached to the camera  100  and when the interchangeable lens  200  is attached. Then, the voltage of the electrical contact  1003  can be made closer (equal) between when the interchangeable lens  600  is attached to the camera  100  and when the interchangeable lens  300  is attached. 
     The camera  100  can determine the type of the interchangeable lens based on the voltage of the electrical contact (first electrical contact)  1003  of the camera  100  when the interchangeable lens is attached, and makes different power to be supplied to the interchangeable lens according to the type of the interchangeable lens. The electrical contact (predetermined electrical contact)  6003  of the interchangeable lens  600  is connected to the electrical contact  1003  when the interchangeable lens  600  is mounted on the camera  100 . 
     The electrical contacts  6006  to  6008  are terminals used for the first communication. The electrical contact  6009  is pulled down to the same level as the DGND terminal  6012  via a resistor. The camera  100  has an electrical contact (second electrical contact)  1009  that is used for data communication with the interchangeable lens  200  and is not used for data communication with the interchangeable lens  300 . When the interchangeable lens  600  is mounted on the camera  100 , the electrical contact  6009  connected to the electrical contact  1009  is connected to the ground via the resistor. Since the interchangeable lens  600  does not perform the second communication, the electrical contact  6009  is an originally unnecessary electrical contact that may not be provided. However, such a circuit configuration can prevent an undefined value from being input to DLC2_IN of the camera controller  101 . If the camera  100  performs processing such as switching DLC2_IN to an output depending on whether or not there is the second communication, the electrical contact  6009  may not be provided. 
     The electrical contacts  6010  and  6011  are not connected to any part in the interchangeable lens  600 . This is because the interchangeable lens  600  cannot perform the third communication. Therefore, the electrical contacts  6010  and  6011  may not be provided with the electrical contacts. The electrical contacts  6010  and  6011  may be grounded via a resistor like the electrical contact  6009 . 
     The interchangeable lens  600  has an operation member operable by the user, and may have an operation member different from the operation member for adjusting the zoom position and the focus position. Such an operation member can change a setting of any of the F-number (aperture position), shutter speed, ISO speed, exposure amount correction, etc., which can be adjusted by the camera  100 . The user can change these settings while viewing through the viewfinder. 
     Functions of Type Terminal 
     Referring now to  FIGS.  6 A to  6 E , a description will be given of functions of the TYPE terminal  1003 .  FIGS.  6 A to  6 E  are schematic diagrams of peripheral circuits of the TYPE terminal  1003 . Now assume that the power supply voltage with which the TYPE terminal  1003  is pulled up in the camera body is 3.3V. A resistor  125  has a resistance value of 100 kΩ, a resistor  126  has a resistance value of 1 kΩ, the resistor  222  has a resistance value of 33 kΩ, and the resistor  622  has a resistance value of 300 kΩ. It is assumed that the voltage value input to the TYPE_IN terminal  101   a  is converted into a digital signal with a resolution of 10 bits by an unillustrated AD converter. 
       FIG.  6 A  illustrates a peripheral circuit of the TYPE terminal  1003  when the interchangeable lens  200  is attached to the camera  100 . In this case, the value input to the TYPE_IN terminal  101   a  of the camera controller  101  is a value obtained by A/D-converting the voltage value obtained by dividing the power supply voltage (3.3 V) by the resistors  125  and  222 , and is approximately “0x0103”. 
       FIG.  6 B  illustrates a peripheral circuit of the TYPE terminal  1003  when the interchangeable lens  600  is attached to the camera  100 . In this case, the value input to the TYPE_IN terminal  101   a  of the camera controller  101  is a value obtained by A/D-converting the voltage value obtained by dividing the power supply voltage (3.3 V) by the resistors  125  and  622 , and is approximately “0x0300”. 
     The resistance values of the resistors  222  and  622  that are made different from each other in this way can make different the value input to the TYPE_IN terminal  101   a  according to the type of the interchangeable lens mounted on the camera  100 . Hence, the camera controller  101  determines the type of interchangeable lens mounted on the camera  100  using the input value of the TYPE_IN terminal  101   a . When the interchangeable lens  300  is attached to the camera  100  via the intermediate adapter  400 , a value corresponding to the resistance value of the resistor  422  of the intermediate adapter  400  is input to the TYPE_IN terminal  101   a . In other words, when the resistance values of the resistors  422  and  622  are made equal, the value input to the TYPE_IN terminal  101   a  of the camera controller  101  is a value obtained by A/D-converting the voltage value obtained by dividing the power supply voltage (3.3 V) by the resistors  125  and  422 , and is approximately “0x0300”. 
     However, if some abnormality occurs in the connection state between the TYPE terminals  1003  and  2003 , an unexpected value may be input to the TYPE_IN terminal  101   a . If the camera controller  101  determines that an interchangeable lens is attached to the camera  100  despite some abnormality, a voltage outside the rating may be applied to the attached interchangeable lens. Accordingly, with reference to  FIGS.  6 C,  6 D, and  6 E , consider a case where some abnormality occurs in the connection state between the TYPE terminals  1003  and  2003 . 
       FIG.  6 C  illustrates a peripheral circuit of the TYPE terminal  1003  when the TYPE terminals  1003  and  2003  do not contact each other due to a poor contact or the like even though the interchangeable lens or the intermediate adapter has been attached to the camera  100 . In this case, the voltage value input to the TYPE_IN terminal  101   a  is determined only by the resistor  125  (100 kΩ) in the camera  100 , and the A/D converted value is approximately “0x03FF”. 
       FIG.  6 D  illustrates a peripheral circuit of the TYPE terminal  1003  when the TYPE terminals  1003  and the VBAT terminal  1002  are short-circuited. Now consider a case where the type of the interchangeable lens attached to the camera  100  is determined before power is supplied to the VBAT terminals  1002  and  2002 . When the voltages of the VBAT terminals  1002  and  2002  when no power is supplied are the same as the PGND terminal and the TYPE terminals  1003  and the VBAT terminal  1002  are short-circuited, the voltage of the TYPE terminal  1003  becomes substantially equal to that of the PGND terminal. At this time, the value input to the TYPE_IN terminal  101   a  is determined by the voltage division ratio between the resistors  125  (100 kΩ) and  126  (1 kΩ) in the camera  100 , and is approximately “0x000A”. 
     Now consider a case where the type of the interchangeable lens mounted on the camera  100  is determined after power is supplied to the VBAT terminals  1002  and  2002 . In this case, when the TYPE terminals  1003  and the VBAT terminal  1002  are short-circuited, the VBAT voltage (4.5 V in this embodiment) is applied to the TYPE terminal  1003 . At this time, the value input to the TYPE_IN terminal  101   a  is approximately “0x03FF”. 
       FIG.  6 E  illustrates a peripheral circuit of the TYPE terminal  1003  when the TYPE terminal  1003  and the PGND terminal  1004  are short-circuited. When the TYPE terminal  1003  and the PGND terminal  1004  are short-circuited, the voltage of the TYPE terminal  1003  becomes substantially equal to the voltage of the PGND terminal  1004  (reference potential (ground level) voltage of the VBAT voltage). At this time, the value input to the TYPE_IN terminal  101   a  is determined by the voltage division ratio between the resistor  125  (100 kΩ) and the resistor  126  (1 kΩ) in the camera  100 , and is approximately “0x000A”. 
     As described above, when some abnormality occurs in the connection state between the TYPE terminals  1003  and  2003 , the voltage of the TYPE terminal  1003  becomes substantially equal to the VBAT voltage or the voltage of the PGND terminal  1004 . Accordingly, this embodiment sets a voltage range that does not include the VBAT voltage and the voltage of the PGND terminal  1004  to the range of the voltage of the TYPE terminal  1003  in which it is determined that the interchangeable lens is properly attached to the camera  100 . Table 1 shows a correspondence table of the input value of the TYPE_IN terminal  101   a  and the determination result of the attachment state by the camera controller  101  in this embodiment. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 0x000~ 
                 0x0080~ 
                 0x0280~ 
                 0x0280~ 
                 0x0380~ 
               
               
                   
                 0x007F 
                 0x017F 
                 0x027F 
                 0x037F 
                 0x03FF 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Determination 
                 Error 
                 Interchangeable 
                 — 
                 Interchangeable 
                 Error 
               
               
                 result 
                   
                 lens 200 
                   
                 lens 300 
               
               
                   
                   
                   
                   
                 Interchangeable 
               
               
                   
                   
                   
                   
                 lens 600 
               
               
                 Communication 
                 — 
                 3.0 V 
                 — 
                 5.0 V 
                 — 
               
               
                 voltage 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, if the input value of the TYPE_IN terminal  101   a  is within the range of “0x0080 to 0x017F”, the camera controller  101  determines that the interchangeable lens  200  is attached to the camera  100 . “0x0080 to 0x017F” is the input value of the TYPE_IN terminal  101   a  corresponding to the voltage within the first voltage range in which the voltage of the TYPE terminal  1003  does not include the VBAT voltage or the voltage of the PGND terminal  1004 . Therefore, the camera controller  101  determines that the interchangeable lens  200  (the first type of interchangeable lens) is attached to the camera  100  only when the interchangeable lens  200  is properly attached to the camera  100 . When it is determined that the interchangeable lens  200  is attached, the camera controller  101  performs the first communication with the interchangeable lens  200  at the communication voltage of 3.0V. 
     Similarly, if the input value of the TYPE_IN terminal  101   a  is within the range of “0x0280 to 0x037F”, the camera controller  101  determines that the interchangeable lens  300  or  600  is attached to the camera  100 . “0x0280 to 0x037F” is the input value of the TYPE_IN terminal  101   a  corresponding to the case where the voltage of the TYPE terminal  1003  is within the second voltage range that does not include the first voltage range, the VBAT voltage, or the voltage of the PGND terminal  1004 . Therefore, only when the interchangeable lens  300  or  600  is properly attached to the camera  100 , the camera controller  101  determines that one of the interchangeable lenses  300  and  600  (interchangeable lens of a type different from the first type) has been attached to the camera  100 . When it is determined that either the interchangeable lens  300  or  600  is attached, the camera controller  101  performs the first communication with the attached interchangeable lens at the communication voltage of 5.0V. 
     When the input value of the TYPE_IN terminal  101   a  is within the range of “0x0000 to 0x007F”, the camera controller  101  determines that there is some abnormality in the attachment state between the camera  100  and the interchangeable lens or the intermediate adapter. “0x0000 to 0x007F” is the input value of the TYPE_IN terminal  101   a  corresponding to the case where the voltage of the TYPE terminal  1003  is a fourth voltage range that includes the voltage of the PGND terminal  1004  and does not include the first or the second voltage range. In this case, the camera controller  101  does not communicate with the interchangeable lens attached to the camera body. Thereby, a voltage outside the rating can be prevented from being applied to the interchangeable lens or the intermediate adapter when the abnormality occurs in the connection state of the TYPE terminal. 
     If the input value of the TYPE_IN terminal  101   a  is within the range of “0x0380 to 0x03FF”, the camera controller  101  determines that there is some abnormality in the attachment state between the camera  100  and the interchangeable lens or the intermediate adapter. “0x0380 to 0x03FF” is the input value of the TYPE_IN terminal  101   a  corresponding to the case where the voltage of the TYPE terminal  1003  is the third voltage range that includes the VBAT voltage and does not include the first or second voltage range. In this case, the camera controller  101  does not communicate with the interchangeable lens attached to the camera body. Thereby, the voltage outside the rating can be prevented from being applied to the interchangeable lens or the intermediate adapter when the abnormality occurs in the connection state of the TYPE terminal. 
     As described above, in this embodiment, when the interchangeable lens  200  is attached to the camera  100 , the voltage of the first electrical contact is within the first voltage range. When the interchangeable lens  300  is mounted on the camera  100 , the voltage of the first electrical contact is within the second voltage range. When the interchangeable lens  600  is mounted on the camera  100 , the voltage of the first electrical contact is within the second voltage range. When the third lens apparatus is attached to the camera  100 , the interchangeable lens  600  is supplied with the same voltage by the camera  100  as that when the interchangeable lens  300  is attached to the camera  100 . 
     If the communication voltages of the first communication of the interchangeable lenses  300  and  600  from the camera  100  are equal to each other, the resistance value of the resistor  422  and the resistance value of the resistor  622  may be made different from each other so as to distinguish the interchangeable lenses  300  and  600  from each other. If the resistance values are made different, the input values of the TYPE_IN terminal  101   a  are made different, and the input value ranges of the determination reference are made different, whether the attached interchangeable lens is the interchangeable lens  300  or  600  can be identified. 
     Type of Communication Method 
     Next follows a description of the first communication method among the first communication, the second communication, and the third communication. When the interchangeable lens  200  is attached to the camera  100 , the first communication between the interchangeable lens  200  and the camera  100  is performed by the asynchronous communication as the first communication method or the clock synchronous communication as the second communication method. More specifically, just after the interchangeable lens  200  is attached, the communication with the camera  100  is performed only by the clock synchronous communication, and then the communication is shifted to the asynchronous communication. 
     On the other hand, when the interchangeable lens  300  is attached to the camera  100  via the intermediate adapter  400  and when the interchangeable lens  600  is attached to the camera  100 , the first communication between the interchangeable lenses  300  and  600  and the camera  100  is performed by the clock synchronous communication. However, since the interchangeable lenses  300  and  600  do not support the asynchronous communication, they cannot communicate with the camera  100  via the asynchronous communication. 
     First, the camera  100  communicates by the clock synchronous communication regardless of the attached interchangeable lens. Here, when ID information (individual information) of the attached interchangeable lens is communicated and the support of the asynchronous communication is recognized as in the interchangeable lens  200 , the communication method shifts to the asynchronous communication. For the interchangeable lens such as the interchangeable lenses  300  and  600  that cannot support the first communication method, the communication by the clock synchronous communication continues. This may be determined only by the above TYPE terminal, or may be determined by the above ID information in addition to the TYPE terminal. The second voltage (5.0 V) is set to the interchangeable lenses  300  and  600  based on the determination result using the TYPE terminal described above. 
     After the ID information is communicated, the interchangeable lens  600  sends to the camera  100  information indicating the presence or absence of the operation member capable of changing the setting of any one of the F-number, the shutter speed, the ISO speed, and the exposure correction amount in response to the information request from the camera  100 . In other words, the lens controller (communicator)  601  in the interchangeable lens  600  responds to the first information request received from the camera  100  when the interchangeable lens  600  is attached to the camera  100  using the second communication method, and sends the individual information of the interchangeable lens  600  to the camera  100 . Then, the lens controller  601  sends information indicating the presence or absence of the operation member to the camera  100  in response to the second information request received from the camera  100  after sending the individual information. 
     Referring now to  FIGS.  7 A to  7 C , a description will be given of the first communication method. The first communication method is the asynchronous communication. However, this embodiment illustrates an example optimized for the communication between the camera and the lens instead of the general asynchronous communication. The communication is made using a signal line LCLK that can switch the high level (High) and the low level (Low) of the voltage, a DCL channel that transmits data from the camera  100  to the interchangeable lens, and a DLC channel that transmits data from the interchangeable lens to the camera. The signal line LCLK is a communication line formed via the electrical contact  1008 , the DCL channel is a communication line formed via the electrical contact  1008 , and the DLC channel is a communication line formed via the electrical contact  1007 . 
       FIGS.  7 A to  7 C  are explanatory diagrams of the asynchronous communication. As illustrated in  FIG.  7 A , the camera  100  changing the voltage level of the signal line LCLK from High to Low becomes a notice that a data frame (DataFrame) having a plurality of continuous data can be transmitted from the interchangeable lens  200  to the camera  100 . The transmission of the data frame starts when the lens controller  201  detects that the voltage level of the signal line LCLK is switched from High to Low. One data frame consists of data from the start bit ST to the stop bit SP. On the other hand, for the camera controller  101 , in response to detecting the start bit from the DLC channel, the data frame from the start bit to the stop bit is transmitted via the DCL channel. 
       FIG.  7 B  illustrates a case in which a busy signal is superimposed after the data transmission through the DLC for  FIG.  7 A . While the busy signal is being output, the camera controller  101  sets the signal line LCLK to the Low level and cannot request the next data frame. Although the communication speed is lower than when busy is not superimposed, it is effective when the lens wants to perform the next communication after performing necessary processing according to the communication content. 
       FIG.  7 C  illustrates a case in which the data transmission direction of the DCL channel is reversed and data is transmitted from the interchangeable lens to the camera  100  similar to the DLC channel. This is effective in sending a large amount of data from an interchangeable lens. 
     Thus, the first communication method switches a plurality of communication modes, lowers the communication speed when processing such as the calculation in the interchangeable lens is prioritized, and can maximize the bandwidth when a large amount of data is to be transmitted. 
     Referring now to  FIG.  8   , a description will be given of the second communication method. The second communication method is the clock synchronous communication in which data is transmitted and received in synchronization with a clock signal.  FIG.  8    explains the clock synchronous communication. A communication is made using the signal line LCLK, the DCL channel, and the DLC channel, similar to the first communication method. A clock signal generated by the camera controller  101  is superimposed on the signal line LCLK, a data frame (B7 to B0) having a predetermined data amount is transmitted in synchronization with it, and the Busy signal is superimposed on the signal line LCLK with the transmission of one data frame. 
     The communication can be made without the busy signal, similar to  FIG.  7 A , but in the case of the clock synchronization, the interchangeable lens needs to transmit and receive data in synchronization with the clock transmitted from the camera  100 . Therefore, the busy can be eliminated only when it can be guaranteed that the processing time in the interchangeable lens is completed by the next clock reception. 
     Since the clock signal is output from the camera and the DLC must be output in synchronization with it, it is necessary to set the bit rate in consideration of the propagation delay of the communication. If the delay amount is larger relative to the bit rate, the DLC cannot be output in synchronization with the clock and the communication fails. Particularly in a system in which a plurality of contacts are connected, the propagation delay may increase due to the contact resistance or the like, so it is necessary to set the bit rate with a margin. 
     Thus, the asynchronous communication has a higher degree of freedom in communication timing than that of the clock synchronous communication and is more suitable for frequent data transmissions and receptions or transmissions of a large amount of data than the clock synchronous communication. The asynchronous communication has a higher communication speed than that of the clock synchronous communication. Thus, the CPU and peripheral circuits constituting the lens controller  201  mounted on the interchangeable lens  200  are likely to be larger than the lens controllers  301  and  601  mounted on the interchangeable lenses  300  and  600 . Therefore, in the interchangeable lenses  300  and  600 , design restrictions of the imaging optical system caused by securing the footprints of the CPU and peripheral circuits are less likely to occur than in the interchangeable lens  200 . The cost can be reduced as compared with the CPU and peripheral circuits of the interchangeable lens  200 . 
     The mount structure, circuit configuration, and communication method of interchangeable lens  600  have been described above. The interchangeable lens  600  has an imaging optical system  680  having a relatively short backfocus. Thus, the CPU and peripheral circuits that are not compatible with the asynchronous communication but are compatible with the clock synchronous communication can suppress the footprint and cost increase while ensuring the optical design freedom. 
     Unlike the interchangeable lens  200 , the interchangeable lens  600  pulls down the electrical contacts (TYPE terminal, predetermined electrical contact)  6003  in the interchangeable lens  600  to the same level as the DGND terminal  6012  via the resistor  622 . Thereby, the communication voltage of the first communication becomes the second voltage (5.0V) similar to the interchangeable lens  300 . In other words, when the interchangeable lens  600  is attached to the camera  100 , the interchangeable lens  600  is supplied with the same voltage from the camera  100  as that when the interchangeable lens  300  is attached to the camera  100 . 
     The interchangeable lens  600  is particularly suitable for an optical system (wide-angle lens) whose 35 mm equivalent focal length at the telephoto end is 40 mm or less, and an optical system (macro lens) having a lateral magnification β that satisfies β≥0.5 when focused on the shortest distance (when focused on the shortest distance at the wide-angle end in the case of a zoom lens). These lenses are less likely to need the asynchronous communication such as the high-speed AF and the followability to a dynamic object, and even if they only support the clock synchronous communication, an imaging problem is unlikely to occur. In addition, the interchangeable lens  600  is suitable for an interchangeable lens that does not transmit correction data for image corrections having a large data capacity to the camera  100 . Although it takes a longer time to send the correction data when it does not support the asynchronous communication, this problem does not occur because the lens is unlikely to send the correction data. The interchangeable lens  600  is also suitable for other interchangeable lenses for which sufficient performance can be expected only by the clock synchronous communication. 
     As described above, the lens apparatus according to this embodiment is the lens apparatus (interchangeable lens  600  as the third lens apparatus) that is attachable to and detachable from the image pickup apparatus (camera  100 ). The lens apparatus includes an imaging optical system  680 , a first-shaped mount part  650  engageable with the mount part  150  of the image pickup apparatus, and a communicator (lens controller  601 ) communicable with the image pickup apparatus. Any of a plurality of lens apparatuses including the first lens apparatus (interchangeable lens  200 ) and the second lens apparatus (interchangeable lens  300 ) is attachable to and detachable from the image pickup apparatus directly or via the intermediate adapter  400  or  500 . The first lens apparatus has a mount part  250  engageable with the mount part of the image pickup apparatus, and communicable with the image pickup apparatus using the first communication method. The second lens apparatus has a second-shaped mount part  350  that is not engageable with the mount part of the image pickup apparatus, and is attachable to the image pickup apparatus via the intermediate adapter  400 , and is communicable with the image pickup apparatus by the second communication method different from the first communication method. The communicator can communicate with the image pickup apparatus using the second communication method, and cannot communicate with the image pickup apparatus using the first communication method. 
     This embodiment can provide a lens apparatus and an imaging system, each of which can improve both the optical design freedom and the communication performance. 
     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. 2019-197785, filed on Oct. 30, 2019 which is hereby incorporated by reference herein in its entirety.