A follow focus is a focus control mechanism used in film and video cameras. It is ergonomic rather than strictly necessary; in other words it does not contribute to the basic functionality of a camera but instead allows the operator to be more efficient and precise. It is usually operated by a focus puller but some camera operators prefer to pull their own focus . The mechanism works through a set of gears on the follow focus that are attached to teeth on the focus ring of the lens. These gears feed to a wheel which, when turned by a focus puller, will spin the teeth and thus the ring on the lens. Features: Material completely metal (Gear part if of brass and steel,other part is of aluminum) Gear drive can be mounted from both side.(Works for both right-handed and left handed) This set includes flexible gearbelt can be used with any zoom or prime lenses with a wide range of lens diamters(any size from 46 to 110mm) Adjustable locking systemsMounts onto 15 mm Rod Support (60mm center to center difference). Compatible with industry stand 15mm rods Rail distance60cm Rail diameter 15mm Suitable for: All DSLR cameras,Vedio cameras Package includes: Follow focus x1 matching gear belt x1 (adjustable from 46mm-110mm)