the embodiment of a switching device according to the invention is shown in perspective and exploded views from fig1 through fig3 . fig1 is an exploded view showing the arrangement of switch plates on a plastic camera body 13 ; fig2 is a partially exploded view showing switch plates and buttons assembled to the plastic camera body 13 ; and fig3 is a perspective view showing the assembled switching device . in fig2 and 3 , the plastic camera body 13 is shown by a phantom line . as shown in fig1 and 2 , a photometric switch plate 21 and a release switch plate 22 are supported by portions of the plastic camera body 13 . the photometric switch plate 21 is formed from resilient and conductive plate spring material , in a substantially u - shape . a lower arm 21d forms a lower side of the u - shape , while an upper ( plate spring ) arm 21u forms an upper portion of the u - shape . an upper contact 21x , which acts as a photometric switch ph sw in combination with a shutter release contact arm 19x ( shown in fig2 and 4 ), is formed on the upper arm 21u . the photometric switch plate 21 further includes a terminal 21b extending from the lower arm 21d , to which a signal connection to a microcontroller 25 ( shown in fig7 ) is made . the release switch plate 22 is formed from resilient and conductive plate spring material , and is shaped having a mounting base 22a with a long arm 22l and a short arm 22s extending in the same direction from the base 22a . the long arm 22l is bent up from the base 22a , and has a first contact 22x near its distal end . the first contact 22x acts as a release switch rls sw in combination with a self - timer contact arm 19y ( shown in fig2 and 4 ). the short arm 22s is substantially coplanar with the base 22a , and has a second contact 22y hear its distal end . the second contact 22y acts as the release switch rls sw in combination with the shutter release contact arm 19x ( shown in fig2 and 4 ) and the upper contact 21x . the release plate 22 further includes a terminal 22b extending from the base 22a , to which a signal connection to the controller 25 ( shown in fig7 ) is made . as shown in fig1 a lower resilient locking tab 14 , an upper resilient locking tab 15 , and a middle resilient locking tab 16 extend from the camera body 3 . the locking tabs 14 , 15 , and , 16 are used for mounting the photometric switch plate 21 and release switch plate 22 . from the perspective of fig1 the middle locking tab 16 is separated from the upper locking tab 15 in the vertical direction by a clearance approximately the thickness of the mounting base 22a of the release switch plate 22 , and is positioned to the left of the upper locking tab 15 . the lower locking tab 14 is separated from the middle locking tab 16 in the vertical direction by a clearance approximately the thickness of the lower arm 21d of the photometric switch plate 21 , and is positioned to the right of both the upper locking tab 15 and the middle locking tab 16 . the lower locking tab 14 is provided with an upwardly extending locking hook 14a . similarly , the middle locking tab 16 is provided with an upwardly extending locking hook 16a . one of the features of this embodiment is the supporting and mounting structure for the photometric switch plate 21 and release switch plate 22 , including the locking tabs 14 , 15 , and 16 , and shown in fig1 , and 4 . the lower arm 21d of the photometric switch plate 21 is inserted and locked in the clearance between the lower locking tab 14 and the middle locking tab 16 . each of the locking tabs 14 , 15 , and 16 is resilient , being unitarily formed with the plastic camera body . according to this embodiment , the locking tabs 14 , 15 , and 16 of the plastic camera body 13 slightly bend ( resiliently ) when the switch plates 21 and 22 are mounted to the body 13 , but the plate spring switch plates 21 and 22 may be alternatively formed to be more resilient than the plastic camera body 13 . when the photometric switch plate 21 is inserted , it pushes the locking hook 14a of the resilient lower locking tab 14 downward , and also pushes the resilient middle locking tab 16 slightly upward . the lower side of a camera body portion 13a provides an additional resistance on the side of the lower locking tab 14 opposite the middle locking tab 16 . alternatively , the locking tabs 14 , 15 , and 16 can be formed to slightly overlap in the vertical direction to act against any moment upon insertion . when the trailing edge of the lower arm 21d passes the locking hook 14a , the lower arm 21d snaps into the clearance between the tabs 14 and 16 , and the tabs 14 and 16 elastically snap back to their neutral positions . at this time , a click sound is generated , verifying the proper mounting of the photometric switch plate 21 . the locking hook 14a prevents any movement of the photometric switch plate 21 out of the clearance . thus , the photometric switch plate 21 inserted in the slit is locked into the clearance between the lower locking tab 14 and the middle locking tab 16 by the locking hook 14a . the mounting base 22a of the release switch plate 22 is similarly supported and locked , and is similarly inserted . specifically , the mounting base 22a of the release switch plate 22 is inserted and locked in the clearance between the middle locking tab 16 and the upper locking tab 15 . when the release switch plate 22 is inserted , it pushes the locking hook 16a of the resilient middle locking tab 16 downward , and also pushes the resilient upper locking tab 15 slightly upward . the upper side of the camera body portion 13a provides an additional resistance on the side of the upper locking tab 15 opposite the middle locking tab 16 . when the trailing edge of the mounting base 22a passes the locking hook 16a , the mounting base 22a elastically snaps into the clearance between the tabs 16 and 15 , and the tabs 16 and 15 elastically snap back to their neutral positions . at this time , a click sound is generated , verifying the proper mounting of the release switch plate 22 . the locking hook 16a prevents any movement of the release switch plate 22 out of the clearance . thus , the release switch plate 22 inserted in the slit is locked into the clearance between the middle locking tab 16 and the upper locking tab 15 by the locking hook 16a . as shown in fig2 through 6 , a shutter release button 17 and a self - timer button 18 are depressably supported on a front decorative plate 10 ( shown by a phantom line in fig5 a , 5b , and 6 ). a common switch plate 19 constructed from electrically conductive plate spring material is fixed to the front decorative plate 10 near the shutter release button 17 and self - timer button 18 . specifically , the common switch plate 19 is fixed to the front decorative plate 10 by means of pins 19d passing through a plurality of mounting holes 19a formed on the common switch plate 19 ( as shown in fig4 through 6 ). the front decorative plate 10 is fixed in turn to the plastic camera body 13 . a resilient shutter release contact arm 19x and a resilient self - timer contact arm 19y fork from the ( plate spring ) common switch plate 19 toward the lower portion of the shutter release button 17 and the self - timer button 18 , respectively . the resilient contact arms 19x and 19y are upwardly biased to contact the buttons 17 and 18 , respectively , so that the shutter release button 17 and the self - timer button 18 are held at their undepressed positions . the common switch plate 19 is further provided with a brush 19c to contact a common conductive plate 12 . since the photometric switch plate 22 is mounted in the camera body 13 as shown in fig2 when the front decorative plate 10 is assembled to the camera body 13 to place the common switch plate in the position shown in fig3 the upper contact 21x opposes the shutter release contact arm 19x of the common switch plate 19 . furthermore , since the release switch plate 22 is mounted in the camera body 3 as shown in fig2 the first contact 22x on the long arm 22l opposes the self - timer contact 19y of the common switch plate 19 , and the second contact 22y on the short arm 22s opposes the bottom of the upper contact 21x of the photometric switch plate 21 . thus , when the plates 19 , 21 , and 22 are mounted in the camera body 13 as shown in fig3 and 4 , the second contact 22y , together with the shutter release contact 19x , acts as the release switch rls sw , and the upper contact 21x of the photometric switch plate 21 is positioned between these two contact terminals . a common conductive plate 12 having a first dx contact 12b is fixed on the camera body 13 , and a separate second dx contact 12a is fixed to the camera body 13 near the first dx contact 12b . as shown in fig2 and 3 , a film cartridge 11 , to be placed in a cartridge chamber of the camera body 13 , is provided with a dx code conductive pattern 11d on the outer surface thereof . dx code conductive patterns used on film cartridges have standardized binary code patterns of conductive portions and non - conductive portions , each distinctive dx code pattern representing a certain film speed . within the many standard dx code patterns , some patterns are alike in one or more of the conductive or non - conductive portions of the pattern . more specifically , in some cases , similar film speeds are alike in at least some portions of the identifying dx code pattern . for example , a specific portion of the various dx code conductive patterns is non - conductive for all standard film speeds under iso 400 , and conductive for all speeds including iso 400 and above . in the context of this specification , a dx code pattern portion in a predetermied position that defines an exclusive set of film speeds , is defined as a &# 34 ; shared dx code portion &# 34 ;. the film cartridge 11 shown in fig1 through 3 is shown with a shared dx code portion 11e . fig7 shows a schematic including a controller 25 , release switch rls sw , photometric switch ph sw , the common conductive plate 12 , the first and second dx contacts 12b and 12a , and a shared dx code portion 11e . as shown in fig7 inputs of the controller 25 , connected to the release switch rls sw and the photometric switch ph sw , are tied high . furthermore , the dx contacts 12a , 12b , combined with the shared dx code portion 11e , act as a shared portion detection switch dx sw . an input of the controller 25 , connected to the shared portion detection switch dx sw , is tied high . as shown in fig1 through 4 , a connection to ground is provided for each of the switches rl sw , ph sw , and dx sw by the common conductive plate 12 . a portion ( dx contact 12b ) of the shared portion detection switch dx sw is unitarily formed with the common conductive plate 12 . the self - timer contact arm 19y of the release switch rls sw , and the shutter release contact arm 19x of the photometric switch ph sw are connected to the common conductive plate 12 ( as ground ) by the brush 19c . the controller 25 controls a metering sensor ( not shown ) and self - timer circuit ( not shown ) when one of the shown switches is turned on or off . as shown in fig1 through 3 , when a film cartridge 11 is inserted in the camera body 13 , the dx contacts 12a and 12b contact the shared dx code portion 11e of the dx code conductive pattern 11d of the film cartridge 11 . thus , using the shared portion detection switch dx sw , the controller 25 detects which group of two exclusive film speed groups ( for example , one of &# 34 ; below iso 400 &# 34 ; or &# 34 ; iso 400 and above &# 34 ;) to which a film inserted in the cartridge chamber belongs , according to the dx code shared portion 11e . if no film is inserted , the controller 25 defaults to one of the exclusive groups . as shown in fig5 a and 8 , during a normal shutter release operation , when the shutter release button 17 is half depressed , the shutter release contact arm 19x of the common switch plate 19 moves down to electrically contact the upper contact 21x of the photometric switch plate 21 . as shown in fig8 the controller 25 detects the closing of the photometric switch ph sw ( that is , a portion of the common switch plate 19 contacts the photometric switch , plate 21 ), and a photometric measurement is taken in response . then , when the shutter reease button 17 is further depressed , as shown in fig5 b , the shutter release contact arm 19x of the common switch plate 19 , the upper contact 21x of the photometric switch plate 21 , and the second contact 22y of the release switch plate 22 all contact . as shown in fig8 the controller 25 detects the closing of both the photometric switch ph sw and the release switch rls sw ( that is , portions of the common switch plate 19 contact both of the photometric switch plate 21 and release switch 22 ), and the exposure operation is carried out in response . as shown in fig6 and 9 , when the self - timer button 18 is depressed , the self - timer contact arm 19y of the common switch plate 19 moves accordingly down to electrically contact the first contact 22x of the release switch plate 22 . consequently , the controller 25 detects that the release switch rls sw is closed ( that is , that a portion of the common switch plate 19 contacts the shutter release plate 22 ), but that the photometric switch ph sw is not , and a preset self - timer circuit ( not shown ) is operated in response . in this case , even though the photometric switch ph sw is not turned on , the photometric measurement is instructed by the self - timer circuit just prior to the exposure operation . as described above , a self - timer operation is readily carried out , and the switching device of the camera having a simple structure and improved assembly efficiency is provided . the present disclosure relates to subject matter contained in japanese patent application no . hei 06 - 326323 , filed on dec . 27 , 1994 , which is expressly incorporated herein by reference in its entirety .