An interchangeable lens (1) with a locking device (2, 2') for system cameras is described, wherein an orientation marking (4) for mounting the locking device (2, 2') on the camera is provided at the end of the lens housing (3) facing the camera, and the contact surface (6) of the locking device (2, 2') has a latching depression (8) at a distance from the orientation marking (4) counter to the direction (7) of rotation of the locking operation and the contact surface (6) contains at least two, preferably six, surface areas (10) which are situated next to one another in an isolated fashion at a distance from the latching depression (8) counter to the direction (7) of rotation within an angle segment of from 100.degree. to 160.degree., preferably 110.degree. to 150.degree., and can be detected individually by optical means.