cam ring 8 the cam ring 8 defines on its periphery a gear segment which engages a tooth rack formed in an elongated sliding member 20 which is coupled to a control element 9 provided with markings 10 the cam ring 8 is also formed on its periphery with a first movable cam 11 which in this example is formed without any inclined portion this first movable cam 11 is assigned to the daylight exposure range of the camera the cam 11 adjoins a second movable cam 12 which is assigned to the flash exposure range a displaceable control lever 13 is biased by a spring 14 into engagement with one of the movable cams 11 and 12 the control lever 13 is provided with pins 15 and 16 which engage diaphragm blades 17 and 18 in front of the objective 1 as long as the control lever 13 engages the first movable cam 11 the pins adjust the diaphragm aperture to a stop value 8 corresponding to the daylight exposure range when the cam ring 8 is rotated into the flash exposure range the movable cam 12 displaces the control lever 13 and the pins adjust the diaphragm blades 13 and 18 to such a position which defines an aperture having a stop value 4 for example markings 10 on the control element 9 are movable in front of a fixed distance scale 19 pertaining to the daylight exposure range in this manner when markings 10 on the control element 9 are moved in front.