A television camera lens mount of the 16-mm format, 1 inch in diameter with 32 threads per inch. CCTV lenses are available in two different lens mounts. "C-mount" lenses have a flange back distance of 17.5mm Vs 12.5mm for "CS-mount" lenses. Many of today's cameras can accept either type of lens, but it is important to make sure that camera and lens are compatible and set up properly. C-mount lenses can be used on CS-mount cameras by utilizing a 5mm adapter or adjusting the camera for C-mount lenses. Because of the shorter back focal distance, CS-mount lenses can only be used on CS-mount cameras. Your picture will be out of focus if you use a CS-mount lens on a C-mount camera.