The advantage to a C-Mount Camera is that the lens can be changed. If you need to see further than 35 or 40 ft then you'll need a c-mount camera with a special lens. C-Mount lenses are available from 4mm to 50mm. A 4mm lens provides facial detail and a 70 degree angle of view focused up to about 35 ft. An example of where you might use a fixed 4mm lens is in a small office, or at home to focus on your driveway.