fig1 schematically shows an outer appearance of a first embodiment of the present invention in which a photographing data setting apparatus of the present invention is applied to a single - lens reflex camera with an interchangeable lens . fig1 shows a state wherein a lens of the camera is detached . a camera body 1 is provided with a release button 2 , a dial 3 as a rotary operation member for setting a value of photographing data , and switches 4 , 5 , and 6 for selecting types of photographing data . the switches 4 , 5 , and 6 are respectively a selection switch , a sensitivity switch , and a mode switch . peripheral portions of the dial 3 project from the front and rear surfaces of the camera body 1 , respectively . the selection switch 4 is arranged near the rear - surface projecting portion of the dial 3 to be responsive to only a dial operation from the rear surface side . it can be discriminated in accordance with the selection switch 4 whether the portion of the dial 3 projecting from the rear or front surface of the camera body 1 is operated . therefore , a photographer can operate a portion of the dial 3 projecting from the front surface of the camera body 1 with his or her first finger or can operate a portion of the dial 3 projecting from the rear surface of the camera body 1 with his thumb to simultaneously select and set desired photographing data . fig2 is a block diagram of a portion associated with selection and setting of photographing data . as shown in fig2 the dial 3 is provided integrally with electrodes constituted by a common electrode portion and two comb - shaped electrode portions having different phases . contact terminals fixed to stationary members ( not shown ) are arranged at positions opposing these electrodes . when the dial 3 is turned , two pulse signals having different phases according to the turning direction of the dial are generated at the contact terminals corresponding to the comb - shaped electrode portions . the contact terminals outputting these pulse signals are connected to an up / down counter 21 . the up / down counter 21 detects the phase relationship between the two pulse signals , switches up - counting and down - counting in accordance with a phase shift direction , and counts one of the up - and down - counting pulses . in this manner , the up / down counter 21 counts pulses according to the turning direction and turning amount of the dial . the switches 4 , 5 , and 6 are connected to a data selector 22 for determining photographing data to be changed by the value of the counter . the data selector 22 selectively turns on switches 23a , 23b , 23c , 23d , 23e , and 23f in accordance with the operations of the switches 4 , 5 , and 6 to supply the outputs from the up / down counter 21 to an exposure mode holding section 24a , a film sensitivity holding section 24b , a shutter speed holding section 24c , an aperture value holding section 24d , an exposure correction value holding section 24e , and a program shift value holding section 24f in a photographing data holding section 24 , thus selectively setting / updating the data . these holding sections 24a to 24f comprise registers , respectively . the switches 4 , 5 , and 6 will be respectively referred to as &# 34 ; selection &# 34 ;, &# 34 ; sensitivity &# 34 ;, and &# 34 ; mode &# 34 ; switches , and fig3 shows selection contents of types of photographing data when the dial 3 is turned while each of the &# 34 ; selection &# 34 ;, &# 34 ; sensitivity &# 34 ;, and &# 34 ; mode &# 34 ; switches 4 , 5 , and 6 is on . when the dial is turned while the sensitivity switch 5 is on , a film sensitivity is changed like iso25 , iso50 ,..., iso3200 . when the dial is turned while the mode switch 6 is on , an exposure mode is changed to a program mode , an aperture priority mode , a shutter priority mode , a manual mode , and the like in turn . when the sensitivity and the exposure mode are set , the dial 3 can be operated from either the front or rear surface side . thus , the sensitivity and the exposure mode can be set when the dial is operated in either direction . a case after the exposure mode has been set will be described below . when the exposure mode is the program mode , if the dial 3 is turned from the front surface side of the body 1 ( with the first finger ), a program shift value is changed since the selection switch 4 is off . in this state , if the dial 3 is turned from the rear surface side ( with the thumb ), it can be pivoted while the selection switch 4 is on , so that an exposure correction value is changed . the program shift value indicates an amount for shifting a program chart for exposure control . the program chart is expressed as shown in fig1 , and a program shift operation is to select one of a plurality of program lines between - 2 to + 2 shown in fig1 . when the exposure mode is the aperture priority mode , if the dial 3 is turned from the front surface side of the body 1 , the aperture value is changed since the selection switch 4 is off ; if it is turned from the rear surface side , an exposure correction value is changed since the selection switch 4 is on . when the exposure mode is the shutter priority mode , if the dial 3 is turned from the front surface side of the body 1 , a shutter speed is changed ; if it is turned from the rear surface side , the exposure correction value is changed . when the exposure mode is the manual mode , if the dial 3 is turned from the front surface side of the body 1 , the aperture value is changed ; if it is turned from the rear surface side , the shutter speed is changed . fig1 is an internal circuit diagram of the data selector 22 shown in fig2 . a second embodiment of the present invention , as a detailed arrangement of the present invention , will be described below . this embodiment exemplifies an arrangement of the selection switch 4 shown in fig1 in more detail . in fig4 a selection switch 4 has contacts 4a and 4b . the contacts 4a and 4b are turned on / off upon operation of a cover member 10 which covers a rear - surface portion of a dial 3 excluding a portion near a distal end face on the rear surface side and is movable in a back - and - forth direction . the cover member 10 is always biased by a spring 11 in a direction toward the rear surface , and is held at a predetermined position to cover most of the rear - surface portion of the dial 3 . when the dial 3 is turned from the front surface side , the cover member 10 is not moved , as shown in fig5 and the selection switch 4 is off . for example , in the aperture priority mode shown in fig3 the aperture value is changed . when the dial 3 is turned from the rear surface side , the cover member 10 is pushed forward , as shown in fig6 to turn on the selection switch 4 . for example , in the aperture priority mode in fig3 the exposure correction value is changed . in fig4 the cover member 10 covers the upper and lower surfaces of the dial 3 . alternatively , a flat member may be arranged above or below the dial 3 . the spring 11 may also serve as a contact portion of the switch 4 . letters &# 34 ; av &# 34 ; indicating an aperture value , &# 34 ;±&# 34 ; indicating exposure correction , and the like may be printed on the upper surface of the cover member 10 , so that a user can externally confirm the type of selected photographing data . a third embodiment of the present invention will now be described . this embodiment exemplifies the selection switch 4 shown in fig1 different from that in the second embodiment . as shown in fig7 a light - emitting diode 12 and a light - receiving element 13 are arranged at two sides of an exposure portion of a dial 3 on the rear side of a camera body 1 to oppose each other . the light - emitting diode 12 and the light - receiving element 13 are arranged as shown in fig8 when viewed from the top such that light emitted from the light - emitting diode 12 to the light - receiving element 13 is shielded by a finger upon operation of the dial 3 from the rear surface side . the light - receiving element 13 comprises , e . g ., a phototransistor , as shown in fig9 and its output is connected to a data selector 22 . in this manner , reliability can be improved by using a non - contact detection means . in this embodiment , a so - called &# 34 ; photointerruptor &# 34 ; is constituted by the light - emitting diode 12 and the light - receiving element 13 . alternatively , a so - called &# 34 ; photoreflector &# 34 ; which receives light reflected by a finger may be employed , thus providing the same effect . a fourth embodiment of the present invention will be described below . this embodiment exemplifies the selection switch 4 shown in fig1 different from those in the second and third embodiments . as shown in fig1 , a rotating shaft 14 of a dial 3 is supported to be movable along a movement groove 15 formed in a camera body 1 . the rotating shaft 14 is always biased in a direction of the rear surface by a spring 16 arranged between itself and the camera body 1 . contacts 4a and 4b of a selection switch 4 are enabled by the rotating shaft 14 . when the dial 3 is to be turned from the rear surface side , as shown in fig1 , the dial 3 is moved forward , and the contacts 4a and 4b of the switch 4 are brought into contact with each other to be electrically connected . a fifth embodiment of the present invention will be described below . this embodiment exemplifies the selection switch 4 shown in fig1 different from those in the second , third , and fourth embodiments . as shown in fig1 , conductive contact patterns 17 and 18 are formed on the upper and lower surfaces of a dial 3 . these conductive patterns 17 and 18 are connected to a circuit shown in fig1 to form a so - called &# 34 ; touch sensor &# 34 ;. the operation of the dial 3 from the rear surface side can be detected by the touch sensor constituted by these contact patterns 17 and 18 . one of the contact patterns 17 and 18 need not always be arranged near the dial but may be arranged at , e . g ., a grip portion of a camera body 1 . in each of the first to fifth embodiments , the dial 3 projects from the front and rear surfaces of the camera body 1 . however , the dial 3 need not project but may be merely exposed as long as it can be operated . the projecting or exposing portions may 1 provided at two positions in the right - and - left direction of the front or rear surface . in addition to the front and rear surfaces , a projecting portion may be provided at a side surface , and a detection means such as a photographing data selection switch may be added . fig1 a and 17b illustrate a case wherein the dial projects from two portions in the right - and - left direction on the rear surface side . fig1 a and 18b illustrate a case wherein the dial projects from one portion on the front surface side and from two portions in the right - and - left direction on the rear surface side . a member 10 &# 39 ; shown in fig1 a and 18b is a member for detecting a dial operation from the right side of the rear surface . when the dial is operated from the right side of the rear surface , the member 10 &# 39 ; is slid to turn on a detection switch 4 &# 39 ;. in fig3 when the dial 3 is turned while depressing the sensitivity switch 5 and the mode switch 6 , the selection switch 4 is invalidated . in a sixth embodiment of the present invention , as shown in fig1 , a switch 5 is used as a switch for selecting a film sensitivity / exposure mode , and a selection switch 4 is used as a switch for selecting one of the film sensitivity and the exposure mode . if multiple depression of these switches 4 and 5 is validated , the following operations are allowed . table l______________________________________function of switch 5 film sensitivity / exposure modewhile depressing switch 5dial front surface dial rear surfacesetting of setting of exposurefilm sensitivity modeexposure without depressing switch 5mode dial front surface dial rear surface______________________________________p program shift exposure correctionav aperture value exposure correctiontv shutter speed exposure correctionm aperture value shutter speed______________________________________ ( the exposure mode includes p : program mode , av : aperture priority mode , tv : shutter priority mode , and m : manual mode .) for example , the following operations are allowed , and the number of operation members can be reduced , thus improving operability . ( 1 ) when the dial is operated from the front surface side while depressing the switch 5 , a film sensitivity setting operation is selected . ( 2 ) when the dial is operated from the rear surface side while depressing the switch 5 , an exposure mode setting operation is selected ( in this case , the exposure mode is changed to the program , aperture priority , shutter priority , and manual modes in turn ). ( 3 ) ( if the aperture priority mode is selected upon operation in ( 2 )), when the dial is operated from the front surface , an aperture value setting operation is selected ( in this case , if the exposure mode is the program mode , a program shift operation is selected ; if the shutter priority mode , a shutter speed setting operation ; and if the manual mode , the aperture value setting operation ). ( 4 ) when the dial is operated from the rear surface side , if the exposure mode is the aperture priority mode , an exposure correction value setting operation is selected ; if the program mode and the shutter priority mode , the exposure correction value setting operation ; and if the manual mode , the shutter speed setting operation . a similar example will be exemplified below . table 2______________________________________function of switch 5 film sensitivity / exposure modewhile depressing switch 5dial front surface dial rear surfacesetting of setting of exposurefilm sensitivity modeexposure without depressing switch 5mode dial front surface dial rear surface______________________________________p setting of exposure program shift modeav aperture valuetv shutter speedm aperture value______________________________________ ( 1 ) when the dial is operated from the front surface side while depressing the switch 5 , a film sensitivity setting operation is selected . ( 2 ) when the dial is operated from the rear surface side while depressing the switch 5 with the switch 4 being on , an exposure correction value setting operation is selected . ( 3 ) when the dial is operated from the front surface side , an exposure mode setting operation is selected . ( 4 ) when the dial is operated from the rear surface side , if the exposure mode is the program mode , a program shift operation is selected ; if the aperture priority mode , an aperture value value setting operation ; if the shutter priority mode , the shutter speed setting operation ; and if the manual mode , the aperture value setting operation . table 3______________________________________function of switch 5 af / exposure modewhile depressing switch 5 dial rear surfacedial front surface setting of setting of exposurefocus mode modeexposure without depressing switch 5mode dial front surface dial rear surface______________________________________p program shift exposure correctionav aperture value exposure correctiontv shutter speed exposure correctionm aperture value shutter speed______________________________________ ( 1 ) when the dial is operated from the front surface side while depressing the switch 5 , a focus mode setting operation is selected ( the focus mode includes , e . g ., an auto - focus mode , a power focus mode in which a focusing operation is performed by a motor upon a switch operation , and a manual focus mode , and the auto - focus mode also includes a single auto - focus mode in which an auto - focusing operation is stopped when an in - focus state is attained , and a continuous auto - focus mode in which the auto - focusing operation is continuously performed ). ( 2 ) when the dial is operated from the rear surface side while depressing the switch 5 with the switch 4 being on , an exposure correction value setting operation is selected . ( 3 ) when the dial is operated from the front surface side , if the exposure mode is the program mode , a program shift operation is selected ; if the aperture priority mode , an aperture value setting operation ; if the shutter priority mode , a shutter speed setting operation ; and if the manual mode , an aperture value setting operation . ( 4 ) when the dial is operated from the rear surface side , if the exposure mode is the program mode , the aperture priority mode , or the shutter priority mode , an exposure correction value setting operation is selected ; and if it is the manual mode , a shutter speed setting operation is selected . fig1 shows a seventh embodiment of the present invention in which the arrangement shown in the block diagram of fig2 is constituted by a microcomputer ( to be referred to as a cpu hereinafter ). the cpu includes a counter 32a for counting a turning amount of a dial , a turning direction latch 32b for temporarily storing turning direction data detected by a turning direction detector 31 , and an input port 32c for receiving signals from switches 4 , 5 , and 6 . the cpu selects one of photographing data in accordance with input signals from the switches 4 , 5 , and 6 and causes an addition processor 32d to perform addition or subtraction of a value ( setting value ) of the selected photographing data in accordance with the count value and the turning direction latch signal . the resultant photographing data is stored in setting value holding unit 32e . the cpu also has a display driver 32f , and displays photographing data set at that time . fig2 a and 20b are flow charts for the cpu shown in fig1 to process operations in fig3 . in fig2 a and 20b , portions &# 34 ; change iso &# 34 ;, &# 34 ; change exposure mode &# 34 ;, &# 34 ; change shutter speed &# 34 ;, &# 34 ; change exposure correction value &# 34 ;, &# 34 ; change program shift value &# 34 ;, and &# 34 ; change aperture value &# 34 ; represent photographing data to be changed depending on combinations of the depressed switches 4 , 5 , and 6 , and these photographing data are changed by subroutines sub1 to sub6 shown in fig2 a to 21f , respectively . in fig2 a . of steps # 1 to # 7 , a processing loop of steps # 2 , # 3 , # 4 , # 5 , and # 2 is a normal loop when the dial is not operated . if the dial is operated while &# 34 ; exposure calculation &# 34 ; in step # 4 is executed , an operation amount of the dial is input to the counter , and it is determined in step # 5 that the count value of the counter is changed . the flow then advances to photographing data changing processing in step # 6 and subsequent steps . after the changing processing is completed , the flow returns to step # 2 . in an exposure mode change subroutine shown in fig2 b , the exposure mode is represented by 2 - bit data shown in fig2 , and takes one of 0 to 3 upon addition / subtraction of the value of the exposure mode data . of steps # 8 to # 12 in fig2 b , mode discrimination processing in steps # 8 , # 11 , and # 12 is performed in accordance with the exposure mode data . fig2 shows an eighth embodiment of the present invention in which a focus motor and a zoom motor are driven upon operation of a dial . a photographing data holding section includes a focal length data holding section 24g and a distance data holding section 24h , and a value of an up / down counter 21 is input to one of these sections . for example , when a dial is operated without depressing a selection switch 4 ( when the dial is operated from the front surface side ), focal length data is set , and a zoom motor 41 is driven . when the selection switch 4 is depressed and the dial is operated ( when the dial is operated from the rear surface side ), distance data is set , and a focus motor 42 is driven . if these motors are , e . g ., stepping motors which are rotated by a step angle corresponding to a designated pulse count , pulses corresponding to the set data value can be supplied to the motor . if these motors are dc motors , an encoder is provided to a lens to be driven , and an encoder output is compared with the set data value , so that the motors can be driven until a coincidence between these data is obtained .