he Cavision RFD15BC is a Basic Mini Single Wheel Follow Focus mechanism for your mini-DV / prosumer camera. It provides you with a convenient, quick and precise method for controlling the focus on your camera using a knob on the side of the camera without the need to constantly reach over to the front of the lens. Follow focus systems have become a staple of professional photographers and videographers needing to frequently adjust a camera's focus according to changing scenes; hence the name "follow" focus.