Adapter ring

Sometimes the adapter C/CS mount ring can be easily unscrewed together with the cap. If that will accidentally happen, you will not be able to focus the C-mount lens - it will be too close to the sensor. In the other case, you may think of the ring as a part of the camera and do not remove it when using camera with the CS-mount lens - if that will happen you'll be able to focus only on very close objects (i.e. your hand while holding the lens).

Fig.1