A follow focus is usually a compulsory piece of equipment for professional filmmaking, it attaches to the focus ring of a manual lens via a set of rods which are usually 15mm rails to the body of a film or video camera. The Follow Focus unit allows the operator to be more efficient and precise. It is usually operated by a focus puller .
Professional Filmmaking
The mechanism works through a set of gears on the follow focus that are attached to teeth on the focus ring of the lens. The gears feed to a wheel which when turned by a focus puller who will spin the teeth and thus the ring on the lens. A manual lens is usually a requisite for professional filmmaking.