referring to fig1 to 9 and first to fig1 there is shown one embodiment of a lens assembly or mechanical unit for housing and operating an objective and a diaphragm of a camera , the objective having a front member movable for focusing , and the unit including a main support tube or lens barrel 1 . a mounting mechanism for the movable front member comprises an actuating sleeve 2 whose rear end is constituted of a thin tubular wall having distance scales cooperative with an index mark 1a formed on the outer surface of the tube 1 . the tubular wall overlaps and is rotatably fitted over the front end of the tube 1 . the actuating sleeve or focusing ring 2 is fixedly connected to an intermediate sleeve 2 &# 39 ; having outer and inner surfaces on which are formed respective threads engaging with mating threads respectively formed on the inner diameter of the enlarged bore in the front end of the main support tube 1 and the outer diameter of a lens cell 3 in which the focusing member is mounted . though not shown , means is provided for converting rotation of the focusing ring 2 to translation of the lens cell 3 along the optical axis . rearwardly of the main support tube 1 , a collet or ring 4 is provided in fixedly secured relation . the rear end of the collet 4 is increased in inner diameter to afford a space which is occupied by a bayonet member 6 and a front radial flange of an adapter shell 8 . the bayonet member 6 is fixed to the collet or ring 4 by screws 7 , while the adapter shell 8 is freely fitted into the front bore of the bayonet member 6 and seated against the radial shoulder of the collet 4 . the adapter flange has a rear shoulder which serves as a reference surface for abutment against the front panel of a camera housing ( see fig4 ( a )), and on which is fixedly mounted an angular position adjusting pin 10 in radial alignment with an index mark 4a formed on the outer surface of the collet 4 , before the unit is attached to the camera body and after it is detached therefrom . as shown in fig2 the bayonet member 6 is formed with three inturned radial extensions or pawls 6b , 6c and 6d angularly spaced from each other by about 120 degrees to provide three arcuate recesses which are aligned with and generally correspond to radial extensions 25a , 25b and 25c of a mating bayonet coupling member 25 ( see fig4 and 5 ) formed on the front panel of the camera housing around its bore for reception of the adapter shell 8 . in the detached position , the aforesaid pin 10 is located in axial alignment with the center of the area of the top recess between the pawls 6b and 6d . axially projected into a space within the recess between the pawls 6b and 6c is an actuating pin 13 for an adapter shell locking mechanism or releasable interlocking means of which the details are shown in fig3 . this mechanism further includes a detent pin 14 seated in a fitted axial hole 4b formed in the inturned radial flange of the collet 4 and biased by an expansion spring 15 to project into an accommodating hole 8c formed through the wall of the radial flange of the adapter shell 8 , when the actuating pin 13 freely fitted in this accommodating hole is not depressed . when the adapter shell 8 is slidably inserted into the bore of the camera housing to the full axial length thereof , the interface between the actuator pin 13 and the detent pin 14 is moved to coincide with that between the adapter shell 8 and the collet 4 to enable the operator to turn the collet 4 with the bayonet member 6 about the axis of the objective or of the lens assembly in a tightening direction by grasping the main support tube or lens barrel 1 , while maintaining the adapter shell 8 stationary relative to the camera housing , as the pin 10 is retained by a corresponding detent recess or slot 25a &# 39 ; formed in the front panel of the camera housing as shown in fig4 ( b ). it should be understood that the collet or ring 4 is fixed relative to the lens barrel 1 and that rotation of the barrel 1 will effect simultaneous rotation of the ring 4 and of the bayonet member 6 . in fig3 the diaphragm presetting mechanism includes an actuating member or diaphragm ring 5 rotatably fitted on the lens barrel 1 at a recess adjacent the front end of the barrel 1 and having a diaphragm value scale formed thereon and cooperative with the common index mark 1a of the distance scale . a cam ring 17 is movably mounted on the barrel 1 and has an inner diameter which is tapered or eccentrically formed in part to provide a camming surface 17a . a driving spring 19 is connected between the lens barrel 1 and an axially upwardly or rearwardly extending projection 17 ( b &# 39 ;) of the cam ring 17 to urge the latter to follow the diaphragm ring 5 by engagement of the projection 17 ( b &# 39 ;) with the lug 5a which projects through and internally beyond a circumferential slot of certain angular extent formed through the wall of the barrel 1 so that any diaphragm value selected on the scale by turning the diaphragm ring 5 to place that value in alignment with the index mark 1a can be introduced into the cam ring 17 . the diaphragm closing down mechanism or operating means includes an operating member 12 rotatably mounted in the lens barrel 1 and having an axially rearwardly extending arm 12a which projects through and outwardly beyond an arcuate slot 9b provided through a rear end cross - wall 9 of the adapter shell 8 and is retained at an initial point near the left - hand terminal end of the slot 9b as viewed in fig2 by a first retaining spring 26 which is engaged between the lens barrel 1 and the operating member 12 . with the lens assembly mounted on the camera , the operating ring 12 will be in a position to contact the driving member c2 disposed within the camera . when the camera is released , this operating ring or member 12 is automatically actuated at the arm end 12a by a drive member c2 in the camera body to move against the force of the retaining spring 26 through the almost full length of the slot 9b , and after the completion of an exposure to return to the initial position illustrated under the action of the spring 26 . in the first half cycle of operation of the ring 12 , a semi - circular member 20 which is linked to a diaphragm blade control ring 21 through an axially upwardly or rearwardly extending arm 21a is turned under the action of a drive spring 21a from an initial position where the diaphragm aperture is fully open to a presetting controlled by the cam ring 17 , and as a result a lug 12b of the operating ring 12 in engagement with an upwardly or rearwardly extending end portion 20a permits rotation of the member 20 and consequently of the diaphragm ring 21 while a cam follower pin 20b fixedly mounted on the opposite end of the semi - circular member 20 abuts against the camming surface 17a of the ring 17 . one of the diaphragm blades is indicated at 22 . actuation of the diaphragm blades 22 under the action of the spring 21a may then occur to an extent determined by the shape and position of the caming surface 17a which determines the aperture opening . a mechanism is provided for introducing either a manually set or an automatically adjusted value of diaphragm aperture to or from that part of an automatic exposure control apparatus which is incorporated in the camera body , when used in the diaphragm or shutter preselection automatic exposure range respectively . this mechanism comprises a transmission member in the form of an intermediate ring 11 having an axially upwardly extending transmission arm 11a which projects through and outwardly beyond an arcuate slot 9a provided through the wall 9 of the adapter shell 8 , said slot 9a being concentric to the slot 9b and angularly spaced therefrom by a distance of about 90 degrees measured at their initial ends , with a tension spring 18 being connected between the extension 17b &# 39 ; of the presetting control cam ring 17 and a lug 11b downwardly extending from the intermediate ring 11 the spring 18 being arranged to bring the extension 17b &# 39 ; and the lug 11b into operative engagement with each other when the lens assembly unit is coupled with the camera body where the various components of the lens assembly will be at the position illustrated in fig6 . in order to retain the transmission arm 11a in the initial or predetermined position after the unit is detached from the camera body while permitting the diaphragm ring 5 to remain unchanged from any set position to the aperture fully open position , there is provided a drive member 23 fixedly mounted on the radial flange of the collet 4 by fasteners 24 in combination with an upwardly extending projection 17b of the cam ring 17 . with the diaphragm ring 5 set in the position for the minimum possible size of diaphragm aperture , when the lens barrel 1 together with the coupling means 6 is turned with respect to the camera body and the adapter shell 8 in the opposite direction to the tightening one , the cam ring 17 is driven by the drive member 23 to move against the force of the drive spring 19 until the arm 11a abuts against the terminal end of the slot 9a . at diaphragm settings of larger aperture sizes , the spring 18 serves as a second retaining spring . in fig7 to 9 , there is shown a mechanism for locking the unit on the camera in the fully tightened position where the entire effective range of movement of the diaphragm responsive or transmission ring 11 can be assured as no mechanical interference between the drive member 23 and the extension 17b occurs . this mechanism comprises an actuating button 101 slidably fitted in a radial hole 4a which is formed in the thickened front part of the collet 4 adjacent the front shoulder of the flange of the adapter shell 8 , a bias spring 102 urging the actuating button 101 to project outwardly beyond the hole 4a , and a detent radial recess 8a formed in the flange of the adapter shell 8 and arranged to receive a rearwardly extending projection 101a of the actuating member 101 when the collet 4 is turned from the position of fig2 to the position of fig8 . this locking mechanism also serves as a mechanism for preventing accidental disengagement of the unit from the camera body . the operation of the unit of fig1 to 9 is as follows : the operator will first manipulate the unit to effect axial alignment of the index mark 4a with the corresponding mark ( not shown ) on the front panel of the camera housing , and then insert the adapter shell 8 at its rear end outer diameter 8a into the bore of the camera housing by grasping the main support tube or lens barrel 1 , whereby the bayonet members 6 and 25 are placed in mating relation to each other . at the terminal end of axial movement of the unit , the radial shoulder of the adapter shell 8 comes to abut against the front surface of the camera housing , and the relative angular position adjusting pin 10 enters the recess 25a &# 39 ; ( see fig4 ( b )). also , the actuator pin 13 is pushed against the force of spring 15 so that the detent pin 14 is retracted from the hole 8c to enable the operator to perform a tightening operation . as a result , the lens barrel 1 together with all the lens operative components mounted thereon , and with the bayonet member 6 , will be free to rotate relative to the camera and to the adapter shell 8 . during the tightening operation , the main support tube or lens barrel 1 is turned about the axis of the objective in a clockwise direction as viewed from the front together with the diaphragm presetting mechanism supported by the tube 1 , while the adapter shell 8 is maintained stationary relative to the camera . it should be understood that if the lens unit is utilized with a shutter priority camera , the transmission arm 11a will not move when the lens unit is mounted since , with the diaphragm ring in the automatic position , control elements within the camera will retain the arm 11a stationary . when the lens unit is used on an aperture priority camera , the arm 11a will move relative to the slot 9a depending upon the set position of the ring 5 . it will be apparent that such movement will be the result of a spring force basically created by the spring 19 which will become effective when the drive member 23 is moved from the extension 17b to permit rotation of the ring 17 . in either case , the arm 12a will remain stationary relative to the slot 9b since when the lens 1 is rotated to couple the lens unit to the camera , the degree of angular movement thereof will not be sufficient to release the force of the spring 26 tending to hold the arm 12a in abutment with the terminal end of the slot 9b . during this operation the relative angular displacements between the ring 11 and the cam ring 17 and between the operating ring 12 and the tube 1 are absorbed by the respective springs 18 and 26 . when the tightened angular position of the tube 1 reaches about 60 degrees from the initial position of fig3 the locking mechanism for the tube 1 starts to operate so that the projection 101a drops into the recess 8a under the action of the spring 102 . this causes the release actuating button 101 to project outwardly over the outer diameter of the collet 4 as shown in fig8 . since the bayonet member 6 is provided with three circumferential slits 6a of equal angular extent formed in the tubular section thereof in correspondence with the respective pawls 6b , 6c and 6d to thereby impart resilient characteristics thereto , a sufficiently sturdy connection between the unit and the camera body is established in the locked position of fig8 . if the diaphragm ring 5 is initially taken at the aperture fully open position , in this instance , f / 1 . 4 , it is at the terminal end of tightening rotation of the tube 1 that the cam ring extension 17b &# 39 ; starts to engage with the transmission ring lug 11b , as shown in fig6 while the drive member 23 is moved away from the extension 17b to such an extent that when the diaphragm ring 5 is turned to set the maximum possible diaphragm value ( the minimum size of aperture ), the extension 11b does not interfere with the drive member 23 . this occurs because the angular extent of the entire operating range of the transmission ring 11 is smaller than that of tightening movement of the tube 1 . so long as the diaphragm ring 5 assumes the illustrated position for the minimum diaphragm value , namely , 1 . 4 , the transmission arm 11a is retained in the uppermost position of the slot 9a during the tightening operation because of the spring force of the spring 18 . as a result , no stress is applied to the operative connection between the transmission arm 11a and the control member c1 of the camera body . in the diaphragm pre - selection automatic exposure range , therefore , the set value of diaphragm aperture by the ring 5 is introduced through the cam ring 17 and transmission ring 11 to the control member c1 in the camera body . an exposure value is thereby derived to control the period of actuation of the camera shutter in accordance with the preselected diaphragm value , object brightness as sensed by the ttl type light metering at the full open aperture , and the sensitivity of the used film . when the shutter release button ( not shown ) is depressed , the control member c2 is actuated to move to the right as viewed in fig2 to actuate the arm 12a with simultaneous occurrence of automatic closing down of the diaphragm blades 22 which continues until the cam follower pin 20b strikes the camming surface 17a at a point dependent upon the set value of diaphragm aperture . after an exposure has been completed , the closing down actuator 12a is returned under the action of the spring 26 to the initial position where the diaphragm blades 22 are fully open . in the shutter preselection automatic exposure range , with the diaphragm ring 5 turned to a point beyond the maximum diaphragm value of the scale , the exposure value is translated to the proper position of the transmission arm 11a . if it is desired to interchange the unit with another one of different rating , the lock release button 101 is first depressed then the tube 1 is turned relative to the camera housing in the opposite direction to the tightening direction until the index mark 4a is aligned with the corresponding mark on the camera housing , and the tube 1 is pulled from the camera body . the adapter shell 8 is locked by the detent pin 14 to the collet 4 . during this unfastening operation , if the diaphragm ring 5 is left set to any value of aperture larger than the minimum one , i . e ., 1 . 4 , then when the drive member 23 is brought into driving engagement with the extension 11b at a corresponding point in the range of movement thereof it pushes the extension 17b against the force of the drive spring 19 until the transmission arm 11a is returned to its initial position . thus , the detached unit when again in use will be easy to handle in establishing operative connection between the diaphragm mechanism in the lens unit and the control device therefor in the camera body . the term &# 34 ; operative connection &# 34 ; herein does not necessarily mean an intimate contact but any spatial relationship which assures later operative connection between the lens unit and the camera body not only directly but through intermediary means such as mechanical switches , variable resistors and electrical contacts . as is evident from the above , all that need be accomplished in establishing accurate and reliable cooperation between the diaphragm and the control device therefor has to do with the achievement of angular alignment of the unit relative to the camera body . further , because no frictional action occurs between the adapter shell 8 and the camera housing during the coupling operation , no error due to wear takes place in the mechanical and optical coordination of the unit and camera body , which error would be otherwise encountered by damage resulting from abrasion and scratching at the bearing surfaces of the lens unit and camera body . furthermore , the collet or ring 4 which in some prior art device is constructed in the form of a movable coupling member is fixedly secured to the main support tube or lens barrel 1 to permit the operator to grasp any part of the lens barrel 1 or of the operative components mounted thereon in order to effect a coupling operation . thus , the accessibility to the coupling device is greatly improved without sacrificing the accuracy and reliability of diaphragm control in the complete camera . the operational mechanical mounting for the coupling device has been described in connection with a purely schematic example which of course can be changed in many ways . for example , instead of a pair of mating bayonet members 6 and 25 , it is possible to use male and female screw threads . in this case , it is recommended that the helix angle be specified to a value such that the required magnitude of the tightening motion of the unit relative to the stationary camera body does not exceed one revolution . instead of a position control pin 10 , it is possible to utilize one of the control members c1 and c2 in defining the angular position of the adapter shell relative to the camera body . in this case , provision must be made for assuring reestablishment of the initial angular position of the adapter shell relative to the main support tube when the unit is detached from the camera body . instead of a main support tube 1 , it is possible to utilize a diaphragm ring 5 in driving a bayonet or screw thread coupling member for rotation to bring the unit into tightened engagement with the camera body . this is exemplified in fig1 , wherein the same reference numerals have been employed to denote similar and like parts to those shown in fig1 to 9 . in fig1 , the collet 4 remains unchanged from the fixedly secured relation to the main support tube or lens barrel 1 . the coupling member 6 is formed integrally with a rotatable sleeve 61 which is fixedly fitted onto the inner surface of the collet 4 by means of screws or the like with the adapter shell 8 being rotatably fitted in an inner circumferential recess of the support sleeve 61 . the support sleeve 61 has an arm downwardly or forwardly extending into either of the paths of movement of two radial projections 5a and 5b of the diaphragm ring 5 . thus , when the diaphragm ring 5 is turned beyond the lower limit ( minimum size of aperture ) of a range of diaphragm values , the first projection 5a is brought into driving engagement with the arm 62 to rotate the bayonet ring 6 in a tightening direction provided that the lock mechanism 13 , 14 and 16 is in the idle position . when the diaphragm ring 5 is turned beyond the upper limit of the diaphragm value range , the second projection 5b is brought into driving engagement with the arm 62 to rotate the bayonet ring 6 in an unfastening direction opposite to the tightening direction . so long as the diaphragm ring 5 is allowed to stand in registry at any one of the available diaphragm values with the stationary index mark 1a , an operative engagement between a lug 5c of the diaphragm ring 5 and an upwardly extending projection 201 of a cam ring 200 is established , the parts 5c , 200 and 201 corresponding to those 5a , 17 and 17b of fig3 and 6 . in order to absorb the tightening and unfastening movement of the diaphragm ring 5 relative to the cam ring 200 , there is provided two tension springs s1 and s2 connected between the projections 5a and 5b and the common ring 200 respectively . the spring s2 also serves to effect the aforesaid operative engagement between the lug 5c and the projection 201 . since the elements of the lens unit including the main support tube or lens barrel 1 , the bayonet member 6 , the sleeve 61 , the collet 4 form a rotatable assembly which is rotatable with respect to the adapter shell 8 and therefore to the camera body through an angular extent of about 60 degrees or more depending upon the structure of the retaining mechanism 11 , 18 and 23 of the invention , it is required to provide a somewhat strong click mechanism between the this rotatable assembly and the adapter shell . otherwise operations of the focusing ring 2 and the diaphragm ring 5 will be difficult to perform , as the complete camera is held by hand at the body thereof . the free rotation of the rotatable assembly relative to the camera housing gives rise to an advantage that the attitude of the camera may be in either of the vertical and horizontal directions , while the index mark 1a is maintained in an upwardly facing position , making it easy to view the distance and diaphragm indicia . instead of utilizing the diaphragm ring 5 as an actuating member for the coupling member 6 , it is possible to provide an independent actuating member as shown in fig1 . this actuating member is constructed in the form of a forwardly elongated portion 300 of the rotatable assembly fixedly fitted thereon . this portion or sleeve 300 is fixedly connected to the bayonet support sleeve 61 by way of a pair of rearwardly extending arms 301 and 302 . if desired , a lock mechanism of the same function as that shown in connection with the fig7 to 9 may be provided not only on the unit of fig1 but also on that of fig1 . this may comprise a detent hole 301a formed in the arm 301 , a pawl member 63 fixedly mounted on the adapter shell 8 and arranged so that when the coupling member 6 has reached a fully tightening position the pawl 63 enters the detent hole 301a , and an actuating member 301c biased by a plate spring 301b whose one end is fixedly carried on the arm 301 and arranged in alignment with the detent hole 301a upon depression to effect disengagement of the pawl 63 from the hole 301a . referring to fig1 , there is shown another embodiment of the present invention applied to a mechanical mounting unit in which the extent of annular movement which must be effected by the rotatable assembly comprising the lens barrel 1 relative to the camera housing in order to effect coupling of the lens unit is smaller than that of angular movement of any one of the transmission members 11a and 12a in returning to their initial predetermined positions . in this connection , it should be noted that with a smaller required angular movement of the lens barrel 1 , the coupling operation is quicker and easier to perform , while with larger angular movement of the diaphragm control signal transmission member 11 , the accuracy of diaphragm control can be effected at a higher level . a problem arising with the embodiment having this feature is that it is not always possible to control retention of the transmission member 11a at the initial position after the unit is detached from the camera body . this second embodiment of the invention is adapted to obviate such problem . to achieve this , there is provided an accelerating device for moving the diaphragm responsive transmission member 11a at a faster rotative speed and through a greater extent of angular movement than that of the main support tube or lens barrel 1 , said device including a cam member 51 fixedly mounted on the bottom surface 8d of the adapter shell 8 and having a camming surface formed on the radially inner side edge thereof in such a configuration that the distance between the axis of the tube 1 and a point at which a radius from that axis intersects the outline of the camming surface 51a is increased with increase in angle as measured in a clockwise direction as viewed from the front of the lens assembly or camera in fig1 . this device further includes a lever 52 fulcrumed at a pin 52a axially upwardly or rearwardly extending from the main support tube 1 , and a longitudinally elongated cam follower pin 53 fixedly mounted on the lever 52 at a nearer distance to the pivot pin 52a than distances of the cam follower pin 53 to points at which the transmission member 11a abuts against the lever 52 while slidably moving thereon . with the diaphragm ring 5 turned to the minimum diaphragm value , in this instance , f / 1 . 4 , in registry with the index mark 1a , when the tube 1 is turned in a counter - clockwise direction indicted by an arrow from the illustrated position to a fully tightened position , the projection 17c of the diaphragm presetting cam ring 17 is moved to engage with the lug 11b of the diaphragm responsive ring 11 which is maintained stationary therethrough by the absorbing action of the spring 18 to retain the arm 11a in the illustrated initial position . during this tightening operation , the accelerating device is moved away from the transmission arm 11a with simultaneous occurrence of clockwise movement of the lever 52 about the pivot pin 52a . as long as the diaphragm ring 5 assumes a setting position in an angular extent beginning with the minimum value , i . e ., 1 . 4 and equal to that of tightening movement of the tube 1 , the aforesaid problem does not take place . now assuming that the diaphragm ring 5 is left set either in the maximum possible value , or in &# 34 ; ee &# 34 ; position , when the tube is turned in a unfastening direction for the purpose of detaching the unit from the camera body , the lever 52 is brought into driving engagement with the arm 11a and moves the latter at a faster angular speed than that of movement of the tube 1 , as the lever 52 is turned in a counterclockwise direction indicated by an arrow by the cam follower pin 53 acting on the stationary cam member 51 against the force of the drive spring 19 for the diaphragm presetting cam ring 17 . at the termination of unfastening movement of the tube 1 , the arm 11a arrives at the initial position , where the tube 1 is locked to the adapter shell 8 by the detent pin 14 to prevent the accelerating device from being driven for movement with the arm 11a by the force of the charged spring 19 which is directly applied to the device because of the displacement of the lug 1a from the projection 17c . fig1 to 15 show a third embodiment of a detachable operational mechanical mounting unit according to the invention including a lens barrel 1 on which a distance adjusting sleeve 2 is rotatably slidably fitted , a front lens cell 3 in which a focusing member of a camera objective is fixedly mounted , said cell 3 being restrained from rotation during focusing , a collet 4 fixedly secured to the rear end of the barrel 1 , a diaphragm ring 5 rotatably fitted on the barrel 1 adjacent the front end of the collet 4 and restrained from axial movement , a female coupling member of the bayonet type 6 fitted onto the inner diameter of the collet 4 and fixedly secured thereto by fasteners 7 , and an adapter shell 8 having a rearwardly elongated tubular portion 8a of an outer diameter equal to the inner diameter of a bore formed in the front panel of the camera housing and around which a male bayonet coupling member is formed on the front panel . the adapter shell 8 is provided with a radial flange formed in the front end thereof and freely fitted onto the inner diameter of a tubular portion of the female coupling member 6 . the rear radial shoulder 8b of the flange 8c serves as an abutment surface when the unit is attached to the camera body , while the front radial shoulder 8d is seated against an inturned radial flange of the collet 4 . positioned on the abutment surface 8b of the adapter flange 8c are an angular relative position defining pin 10 and an adapter locking control pin 13 , these parts having the same functions as those denoted by the same reference numerals in fig1 and 2 . the unit further includes a diaphragm presetting and closing down mechanism with transmission arms 11a and 12a projecting through and outwardly beyond respective arcuate slots concentric to each other and formed in a common rear end crosswall 9 of the adapter shell 8 in angularly spaced relation as shown in fig1 . in the complete camera , while the arm 12a is located adjacent a control member c2 therefor , the arm 11a in the initial position is located at a distance from a control member c1 for a purpose to be described later . the arm 11a extends upwardly or rearwardly of a ring 11 rotatably slidably supported on the adapter shell 8 and having another arm 11b downwardly extending into a slot formed in an upward extension 117b of a presetting control cam ring 117 and freely fitted therein . a drive spring 113 is connected between the arm 11b and the adapter shell 8 to allow the entire range of movement of the transmission ring 11 together with the cam ring 117 . the extension 117b is located to permit movement of a lug 5a of the diaphragm ring 5 thereover . positioned between the transmission ring 11 and the diaphragm ring 5 is an intermediate ring 114 rotatably supported in the barrel 1 and having an inturned radial lug 114a arranged adjacent the arm 11b so that when the unit is in the detached position , the transmission arm 11a is retained in the initial position . with the diaphragm ring 5 set in &# 34 ; a &# 34 ; position beyond the range of diaphragm values available on the peripheral surface thereof , in other words , in proper alignment at a symbol &# 34 ; a &# 34 ; with an index mark 1a , when the lens barrel 1 is turned about the axis thereof in a direction indicated by arrows in fig1 to the fully tightened position , the lug 114a is moved away from the transmission arm 11b to permit automatic adjustment of the cam ring 117 in position . the intermediate ring 114 is provided with an anchor or clutch means in the form of a pin 115 having a round head 115a formed at one end thereof , the opposite end of which projects through a slidably fitted axial hole 114c formed in the body of the ring 114 and downwardly therebeyond to such an extent that when the barrel 1 is turned in the tightening direction to bring the lug or bifurcated member 5a into abutting engagement with a downwardly extending projection 114b of the intermediate ring 114 , the pin 115 is aligned to a detent slot 5b formed in the lug 5a . upon further slight rotative movement of the barrel 1 , the intermediate ring 114 is driven for rotation with simultaneous occurrence of downward movement of the anchor pin 115 away from the recess 8d of v - shape profile formed in the bottom surface 8d of the adapter shell 8 against the force of a bias expansion spring 116 , as a sufficiently strong click mechanism is provided between the diaphragm ring 5 and the base barrel 1 . such downward movement of the anchor pin 115 causes driving engagement of the diaphragm ring 5 at the slot 5b with the intermediate ring 114 at the end 115b of the anchor pin 115 . the diaphragm closing down mechanism includes a transmission ring 12 having the aforesaid arm 12a and rotatably slidably supported on the adapter shell 8 , a retaining tension spring 123 connected between a downwardly extending arm 12b of the transmission ring 12 and the adapter shell 8 to maintain a diaphragm blade control ring 121 normally stationary in an aperture fully open position by engagement of the arm 12b with an upward projection 121a against the force of a drive spring which tends to move the diaphragm blade control ring 121 in a closing down direction , and a bell - crank 120 whose shaft is mounted on the barrel 1 and which has a cam follower pin 120a fixedly mounted thereon and engaged with a camming surface 117a of the presetting control ring 117 to control arrestment of the ring 121 in accordance with the position of the cam ring 117 by a pin 120b which is fixedly mounted on the bell crank 120 and projects into a space in a recess 121b formed in the ring 121 . in operating the unit of such structure , the operator will first look for axial alignment of an index mark 4a provided on the outer periphery of the collet 4 with a corresponding mark ( not shown ) provided on the camera housing . then the unit at the rear end 8a of the adapter shell 8 is inserted into the bore until the abutment surface 8b contacts with the bearing surface of the camera housing , while the pin 10 enters a slidably fitted hole provided on the camera housing simultaneously and the lock control pin 13 is also actuated to release the adapter shell 8 from locking connection with the lens barrel 1 . the barrel 1 is then turned about the axis of the lens therein with respect to the stationary camera housing . during this tightening operation , the adapter shell 8 is maintained stationary relative to the camera housing . now assuming that the diaphragm ring 5 is initially set in an extreme position for the minimum diaphragm value , i . e ., 1 . 4 as shown in fig1 , when the lens barrel 1 nears the terminal end of tightening movement , the lug 5a abuts against the projection 114b . upon further movement of the lens barrel 1 through a length equal to or slightly larger than the above noted distance between the arm 11a and the control member c1 shown in fig1 , the anchor pin head 115a comes to ride on the smooth surface adjacent the recess 8d of the radial flange 8c and the arm 11a is brought into operative engagement with the control member c1 . at the termination of length of such additional tightening movement , the lens barrel 1 is stopped from further rotation by means such as those shown in fig7 to 9 . after that , the diaphragm ring 5 may be turned to place a desired diaphragm value in registry with the index 1a , causing the transmission ring 11 to follow up the intermediate ring 114 under the action of the spring 113 which does not result in disengagement of the ring 114 from the ring 5 because of the anchor pin end 115b engaging in the slot 5a . when the complete camera is switched to a shutter preselection automatic diaphragm control mode by turning the diaphragm ring 5 to place the symbol &# 34 ; a &# 34 ; in registry with the index 1a , the arm 11a is displaced to the opposite terminal end of the slot 9 so that the cam ring 117 is adjusted to an automatic setting from a position corresponding to the fully closed aperture in an opening up direction . when the shutter release button is depressed , the control member c2 is actuated to move in a counter - clockwise direction as viewed in fig1 , and such movement of the member c2 is transmitted through the ring 12 to the diaphragm blade control ring 121 , and the ring 121 is thereby driven by the spring 122 which is weaker than the spring 123 , as the arm 12b is moved away from the extension 121a . after an exposure has been completed , the control member c2 returns to the initial position , while permitting the diaphragm blades to be moved to the full open position under the action of the spring 123 which has overcome the spring 122 . it it is desired to interchange the unit with another one of different rating , the operator need only push the button 101 ( see fig7 ) and then turn the lens barrel in the unfastening direction without the necessity for being aware of the setting position the diaphragm ring 5 is to assume . with the diaphragm ring 5 in &# 34 ; a &# 34 ; position , when the barrel 1 is turned from the fully tightened position , through an angular extent equal to that of the effective operating range of the diaphragm ring from a graduation , 1 . 4 , to the symbol &# 34 ; a &# 34 ;, the control member c1 is just stopped from further movement . upon further unfastening movement , through the distance above noted in fig1 , the head 115a of the anchor pin 115 drops into the recess 8d under the action of the spring 116 , and the transmission arm 11a is thereby retained in the initial position against the force of spring 113 . after that , the lens barrel 1 may be further turned in the unfastening direction through as long a length as desired , provided that the coupling member 6 can be disengaged from the mating one . thus , the unit can be easily interchanged with another one of different focal length rating . another advantage is that the design flexibility of the coupling device is increased allowing an angular extent of tightening movement of the unit to be increased as desired without introducing overstress to the diaphragm transmission mechanism . while specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles , it will be understood that the invention may be embodied otherwise without departing from such principles .