Abstract:
An imaging device is provided that includes a camera body, a lens barrel, a lens barrel information transmitter, and an image sensor driver. The image sensor is housed in the camera body. The lens barrel is attachable to and detachable from the camera body. The lens barrel information transmitter regularly transmits information of the lens barrel to the camera body. The image sensor driver drives the image sensor at one of at least two different frame rates where a second frame rate is higher than a first frame rate. The amount of data being transmitted is reduced by the lens barrel information transmitter when the image sensor is driven at the second frame rate, compared to the amount transmitted when the image sensor is driven at the first frame rate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an imaging device in which data is transmitted between a lens barrel and a camera body provided with an image sensor. 
         [0003]    2. Description of the Related Art 
         [0004]    In an interchangeable-lens camera communication generally occurs between separate controllers located on the camera body and lens barrel through contact points that are provided on a lens mount. For example, instruction signals and synchronous signals for driving the lens and controlling a photographing operation may be fed from the camera body to the controller of the lens barrel. On the other hand, position information of the focusing lens may be fed from the lens to the controller of the camera body (refer to Kokai 2007-322922). 
       SUMMARY OF THE INVENTION 
       [0005]    However, as camera makers increase the number of actuators provided inside the lens barrel, information related to the status of the lens barrel that should be delivered to the camera body in real time is also increasing. As transmitted data increases, the controller of the camera body needs to spend more time in communication. Therefore, the available time for the image sensor operation is reduced because of the data communication between the lens barrel and the lens body, which makes it more difficult to drive the image sensor at a relatively high frame rate. 
         [0006]    Therefore, one aspect of the present invention is to optimize communication between the camera body and the lens barrel while enabling the image sensor to operate at a high frame rate. 
         [0007]    According to the present invention, an imaging device is provided that includes a camera body, a lens barrel, a lens barrel information transmitter, and an image sensor driver. The camera body is provided with an image sensor. 
         [0008]    The lens barrel is attachable to and detachable from the camera body. The lens barrel information transmitter regularly transmits information of the lens barrel to the camera body. The image sensor driver drives the image sensor at one of at least two different frame rates where a second frame rate is higher than a first frame rate. The amount of data being transmitted is reduced by the lens barrel information transmitter when the image sensor is driven at the second frame rate, compared to the amount transmitted when the image sensor is driven at the first frame rate. 
         [0009]    In another aspect of the invention, a lens barrel attachable to and detachable from a camera body equipped with an image sensor is provided. The lens barrel includes the lens barrel information transmitter and a frame rate determiner. 
         [0010]    The lens barrel information transmitter regularly transmits information of the lens barrel to the camera body. The frame rate determiner determines whether the image sensor in the camera body is driven at the first frame rate or at the second frame rate that is higher than the first frame rate. The amount of data being transmitted is reduced by the lens barrel information transmitter when the image sensor is driven at the second frame rate, compared to the amount transmitted when the image sensor is driven at the first frame rate. 
         [0011]    In another aspect of the invention, a camera body from which a lens barrel is attachable and detachable is provided and equipped with the image sensor, a lens barrel information receiver, and an image sensor driver. 
         [0012]    The lens barrel information receiver regularly receives information of the lens barrel. The image sensor driver drives the image sensor at one of at least two different frame rates where the second frame rate is higher than the first frame rate. The amount of data being transmitted is reduced by the lens barrel information transmitter when the image sensor is driven at the second frame rate, compared to the amount transmitted when the image sensor is driven at the first frame rate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The objects and advantages of the present invention will be better understood from the following description with references to the accompanying drawings in which: 
           [0014]      FIG. 1  is a perspective view of an interchangeable-lens camera with a lens barrel attached; 
           [0015]      FIG. 2  is a perspective view of the camera body alone, from which the lens barrel has been removed; 
           [0016]      FIG. 3  is a block diagram showing the electrical construction of the interchangeable-lens camera; 
           [0017]      FIG. 4  is a schematic showing an electrical connection between the camera processor and lens CPU via the contact points; 
           [0018]      FIG. 5  schematically illustrates an example of a time sequence of the normal-mode regular communication between the camera processor and the lens CPU; 
           [0019]      FIG. 6  indicates problems that may occur in a communication sequence without the present embodiment; and 
           [0020]      FIG. 7  shows a communication sequence of the present embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The present invention is described below with references to the embodiments shown in the drawings. 
         [0022]      FIG. 1  is a perspective view of an interchangeable-lens camera with a lens barrel attached.  FIG. 2  is a perspective view of the camera body alone, from which the lens barrel has been removed. 
         [0023]    For the interchangeable-lens camera  10 , the lens barrel  11  is detachable from the camera body  12 . The lens barrel  11  may include a zoom lens as well as a focus lens and be further provided with a focus ring  11 F and zoom ring  11 Z for adjusting the positions of the focus lens and zoom lens, respectively. 
         [0024]    A plurality of contact points  14  is arranged in an arcuate configuration on the inner side of a lens mount  13  of the camera body  12 , and an image sensor unit  15  is installed inside the camera body  12  at the position corresponding to the center of the lens mount  13 . A flash  19  and switches including a release button  16 , an E-dial  17  (a shaft encoder) and a mode dial  18  may be provided on the top of the camera body  12 . 
         [0025]      FIG. 3  is a block diagram showing the electrical construction of the interchangeable-lens camera  10 . In addition to the above-mentioned elements, such as the image sensor unit  15 , the flash  19  and the switches including the release button  16 , the camera body  12  may further include a camera processor  21 , data storage devices such as a DRAM  22  and/or an SD memory card  23 , a monitor  24 , a camera power circuit  25 , a lens power circuit  26 , a battery  27  and so on. 
         [0026]    The image sensor unit  15  may include an image sensor  28  (e.g., CMOS) and an image stabilization system  29 . The image sensor  28  and the image stabilization system  29  are controlled by the camera processor  21 . Images that are captured by the image sensor  28  may be displayed on the monitor  24  as live preview images. When the camera power circuit  25  is turned on, the electric power is supplied to each of the devices on the camera body  12  from the battery  27 . Further, when the lens power circuit  26  is turned on, electric power is supplied to the power circuit of the lens barrel  11  mounted on the camera body  12 . Although a power line and a bus are neglected in  FIG. 3 , all of the elements illustrated in  FIG. 3  are connected to the power line and bus as desired in a manner commonly known in the art. 
         [0027]    Light is made incident on the image sensor  18  through the photographing optical system of the lens barrel  11 , which is attached to the camera body  12 , and an object image is projected on the image sensor  18 . The photographing optical system may include a zoom lens  30 , a mechanical shutter  31 , a neutral density (ND) filter  32 , a stop (e.g. an iris diaphragm)  33  and focus lens  34 . The zoom lens  30  is adjusted in accordance with a rotational operation of the zoom ring  11 Z, and a zoom sensor  35  may detect the position of the zoom lens  30 . 
         [0028]    On the other hand, the focus lens  34  is driven by an autofocus (AF) motor  36  while the release button  16  of the camera body  12  is depressed halfway. However, the position of the focus lens  34  may also be controlled by a rotational operation of the focus ring  11 F. Namely, the position of the focus lens maybe detected by a lens position sensor  38  and the position of the focus ring  11 F by a focus ring sensor  39 . Thereby, the focus lens  34  is moved in response to a rotation of the focus ring  11 F when the focus ring  11 F is hand operated. 
         [0029]    Further, the mechanical shutter  31 , the ND filter  32  and the stop  33  are driven by a shutter motor  40 , an ND motor  41  and a stop motor  42 , respectively. Each of the motors may be driven by a lens CPU  44  inside the lens barrel  11  via a motor driver  43 . 
         [0030]    The lens CPU  44  may be operated by a program stored in a non-volatile memory, such as a flash memory  45 . Electric power is supplied from the lens power circuit  46  of the lens barrel  11  to all of the devices inside the lens barrel  11 . The lens power circuit  46  of the lens barrel  11  is connected to the lens power circuit  26  inside the camera body  12  through some of the contact points  14  (see  FIG. 2 ), which may be referred to as power lines. Namely, when the camera power circuit  25  is activated, the electric power from the camera body  12  is supplied to the lens barrel. 
         [0031]      FIG. 4  is a schematic showing the electrical connection between the camera processor  21  and lens CPU  44  via the contact points  14 . 
         [0032]    Both of the camera processor  21  and the lens CPU  44  include the following terminals: a digital signal ground pin DGND, a general-purpose I/O pin GPIO, an interrupt request pin INT, a serial data input pin SIN, a serial data output pin SOUT, a serial clock pin SCLK, and a lens vertical drive pin LVD for transmitting vertical drive signals. Note that the general-purpose I/O pin and the interrupt request pin INT are cross-connected to each other and also the serial data input pin SIN and the serial data output pin SOUT are cross-connected to each other while pins of the other ports are connected to the same corresponding ports on the other processor. 
         [0033]    Further, in the present embodiment, there are ten electrical contact points  14  and the three terminals other than the above-mentioned seven terminals are connected to a power supply pin (5.0V power supply), a digital ground pin DGND (LDET) for detecting a connection, and a power ground pin PGND. Namely, these three contact points are used to connect the lens power circuit  26  of the camera body  12  to the lens power circuit  46  of the lens barrel. 
         [0034]    The camera processor  21  detects the connection of the digital ground pin DGND of the lens power circuit  46  through the open load detection pin LDET to confirm the attachment of the lens barrel  11 . The lens power circuit  26  is then activated to supply electric power to the lens power circuit  46  through the 5.0V power supply pin and the lens power circuit  46  is activated to supply electric power to each device in the lens barrel  11 . 
         [0035]      FIG. 5  schematically illustrates an example of a time sequence of the normal-mode regular communication between the camera processor  21  and the lens CPU  44 . With reference to  FIGS. 4 and 5 , a basic sequence of the communication between the camera body  12  and the lens barrel  11  will be explained. 
         [0036]    The communication between the camera processor  21  and the lens CPU  44  is carried out per a vertical drive signal for the image sensor  28  (see  FIG. 3 ), which is output from the camera processor  21  via the lens vertical drive pin LVD. The sequence in  FIG. 5  represents an example of the normal-mode regular communication while the normal live preview image is being captured at 60 fps. A communication sequence within one frame is illustrated in  FIG. 5 , as an example. 
         [0037]    Within one frame period, the camera processor  21  and the lens CPU  44  perform a plurality of signal transmissions alternately from either side. In  FIG. 5 , a transmission period for the camera processor  21  is referred to as an interval “A” and a transmission period for the lens CPU  44  is referred to as an interval “B”.  FIG. 5(   a ) represents output from the general-purpose I/O pin GPIO of the camera processor  21  and  FIG. 5(   b ) represents output from the serial data output pin SOUT of the camera processor  21 .  FIG. 5(   c ) represents output from the general-purpose I/O pin GPIO of the lens CPU  44  and  FIG. 5(   d ) represents output from the serial data output pin SOUT of the lens CPU  44 . Further,  FIG. 5(   e ) represents clock signals fed from the camera processor  21  to the lens CPU  44  though the serial clock pin SCLK. 
         [0038]    In the present embodiment, the general-purpose I/O pin GPIO and the interrupt request pin INT are used for counter-handshake operations. Namely, a positive waveform signal from the general-purpose I/O pin GPIO of a data transmitter represents a request for communication, for example, the positive waveform in the interval “A” of  FIG. 5(   a ). On the other hand, a positive waveform signal from the general-purpose I/O pin GPIO of a data receiver represents permission to establish the communication, for example, the positive waveform in the interval “A” of  FIG. 5(   c ). Further, a falling signal from the general-purpose I/O pin GPIO of the data receiver represents the completion of data receipt, for example, the falling edge in the interval “A” of  FIG. 5(   c ). Further, a falling signal from the general-purpose I/O pin GPIO of the data transmitter represents termination of the communication, for example, the falling edge in the interval “A” of  FIG. 5(   a ). 
         [0039]    On the other hand, the serial data output pins SOUT and the serial input pins SIN of the camera processor  21  and the lens CPU  44  are used to transmit data. When the transmitter receives communication permission from the receiver, the transmitter transmits serial data from the serial data output pin SOUT and the serial data is received by the receiver via the serial data input pin SIN. 
         [0040]    In the example of  FIG. 5 , regular instructions are transmitted from the camera processor  21  to the lens CPU  44  during the first interval “A”. In turn, lens data required in the regular instructions are transmitted from the lens CPU  44  to the camera processor  21  in the next interval “B”. 
         [0041]    A frame rate of 60 fps, which is normally used in the live preview, provides a sufficient time interval for transmitting various information representing the status of the lens barrel  11  to the camera body  12 . Namely, in each frame the lens barrel information, which includes data on the AF motor status, focus position, focus ring position, stop motor status, aperture value (AV), focal length, image correction, temperature, drive mode and the like, is transmitted from the lens CPU  44  to the camera processor  21  when a normal live preview image is displayed on the monitor  24  ( FIG. 3 ) at the frame rate of 60 fps, in other words when the image sensor  28  ( FIG. 3 ) is driven at 60 fps. 
         [0042]    However, when the release button  16  ( FIG. 1 ) is depressed halfway, for example, and the contrast detection autofocus (CAF) is carried out, the image sensor  28  is required to be driven at a relatively high frame rate, for example at 120 fps. As the frame rate increases, the time interval of one frame period decreases in inverse proportion; thereby, if the communication is performed under the same clock frequency as in the regular (normal) frame rate (e.g., 60 fps) during the contrast detection autofocus, one frame period may not be sufficient for transmitting all of the information of the lens barrel  11  to the camera body  12 . 
         [0043]    For example, as illustrated in  FIG. 6 , when the frame rate is accelerated to 120 fps to perform the contrast detection autofocus operation, the above-mentioned lens information “N”, which is regularly transmitted at the regular (normal) frame rate, may require over two or more frames at a time point “t 1 ”. Thereby, to which frame the information belongs is unknown in this situation. Further, at a time point “t 2 ”, for example, control instructions “E” (e.g., focus drive instructions, stop drive instructions, ND drive instructions and initializing instructions) that should have been sent in the antecedent frame are transmitted in the subsequent frame, thus the instructions are one frame behind. Further, at a time point “t 3 ”, for example, lens information “N” for this frame in the normal-mode regular communication may not be sent properly. 
         [0044]    Accordingly, in the present embodiment, when the contrast detection autofocus is started and the frame rate is increased from the regular (normal) frame rate to a relatively high frame rate, the information volume of the lens barrel  11  that is transmitted to the camera body  12  is reduced to an amount that can be transmitted within the new frame period. For example, the information of the lens barrel  11  that is transmitted to the camera body  12  is limited to data that is essential to carry out the contrast detection autofocus, such as the focus motor status, focus position and focus ring position, with this data communication hereinafter referred to as CAF regular communication. Namely, the remaining lens barrel information, such as the data pertaining to the aperture value, focal length, image correction, temperature and drive mode, which are not used during the contrast detection autofocus operation, is not transmitted. Instead, only the information required for the contrast detection autofocus operation is transmitted at a relatively high frame rate to accelerate the contrast detection autofocus operation. 
         [0045]    In  FIG. 7  a communication sequence of the present embodiment with reference to the vertical drive signals is shown. Namely,  FIG. 7  shows a situation when the release button is half depressed during the live preview (60 fps) to carry out the contrast detection autofocus (120 fps) and then redisplay the live preview (60 fps) after completion of the autofocus operation. Note that in  FIG. 7  areas surrounded by the broken lines “L 1 ” and “L 2 ” represent intervals when the live preview are carried out (at 60 fps) and the area surrounded by the broken line “C” represents an interval when the contrast detection autofocus is carried out (at 120 fps). 
         [0046]    In the live preview interval “L 1 ”, the camera barrel&#39;s regular information “N” is transmitted from the lens barrel  11  to the camera body  12  in each frame (of normal-mode regular communication). For example, when the camera processor  21  ( FIG. 3 ) detects a half-depressed release button  16  ( FIG. 1 ) in a certain frame during the live preview interval “L 1 ”, an instruction to change the stop value to a value for contrast detection autofocus is transmitted from the camera body  12  to the lens barrel  11  in the next frame. And from the frame after the next frame, the image sensor  28  is driven at the relatively high frame rate (at 120 fps) needed for the contrast detection auto focus. 
         [0047]    In the CAF interval “C” the CAF regular communication, in which less information is transmitted than the normal-mode regular communication, is carried out between the lens barrel  11  and the camera body  12  per each frame. For example, in the first frame under the accelerated frame rate, a search instruction for detecting the peak of the contrast (which corresponds to the in-focus position) is output from the camera body  12  to the lens barrel  11 . When the peak of the contrast (in-focus position) is detected in the CAF interval “C”, an instruction to move the lens to the in-focus position is output from the camera body  12  to the lens barrel  11 . Further, when translation of the focus lens  34  ( FIG. 3 ) is completed in the lens barrel  11  and the in-focus status is achieved, an instruction to change the stop value to the value for the live preview is output from the camera body  12  in the next frame. Further, the frame rate changes to the regular (normal) frame rate (60 fps) in the frame after the next frame to start the live preview interval “L 2 ”. 
         [0048]    As described above, according to the present embodiment the cycle and contents (or the amount) of data transmitted during communication between the camera body and the lens barrel are changed with respect to an operational situation of the camera so that efficient communication compatible to each frame rate can be carried out and the image sensor can also be driven at a relatively high frame rate. 
         [0049]    Although the embodiment of the present invention has been described herein with reference to the accompanying drawings, obviously many modifications and changes may be made by those skilled in this art without departing from the scope of the invention. 
         [0050]    The present disclosure relates to subject matter contained in Japanese Patent Application No. 2011-160093 (filed on Jul. 21, 2011), which is expressly incorporated herein, by reference, in its entirety.