Abstract: A mechanical linkage in a focal plane shutter type of camera which prevents insertion of a flash attachment to the mating shoe of the camera and insertion of a flash cord in the X synchronization socket of the camera unless the camera shutter speed control knob is set for a shutter speed within the proper range for use with the flash attachment. Conversely, the linkage prevents rotation of the shutter speed control knob beyond the proper range for use with flash apparatus when a flash attachment is mounted to the shoe of the camera or a flash cord has been inserted in the X synchronization socket of the camera.