Aluminum or stainless steel gear ring mounted on a lens to enable precise focus pulling with follow-focus systems.
Technical Details
Standard focus gears are made of anodized aluminum or stainless steel with a width of 6-10 mm and variable diameters between 60-120 mm. The gear geometry follows the 0.8 module standard (32 diametral pitch), resulting in a tooth pitch of exactly 0.8 mm. Mounting is done via set screws (usually three 1/4"-20 or M3 threads) or by elastic expanding rings. High-quality versions feature hardened tooth flanks with a Rockwell hardness of 58-62 HRC and manufacturing tolerances of ±0.02 mm.
History & Development
The standardized focus gear became established in 1985 with the introduction of professional follow focus systems by Arri and Panavision. Previously, individual friction drive solutions with inconsistent diameters were used. The 0.8 module standard prevailed with Arri's introduction of the FF-4 follow focus system and became the de facto industry standard in 1990. Modern developments include self-adhesive focus gears (since 2010) and carbon composite variants for weight-critical gimbal setups.
Practical Use in Film
Focus gears enable precise focus shifts during demanding camera movements. For example, Roger Deakins used motorized follow focus systems with gears for millimeter-accurate focus ramps during the Steadicam one-takes for the prison sequences in "1917" (2019). Standard workflow: Mount focus gear before shooting begins, calibrate focus marks, test all focus points. Advantage: Reproducible focus positions and smooth movements. Disadvantage: Additional weight of 80-150 grams per lens.
Comparison & Alternatives
Focus gears differ from friction drives through slip-free power transmission without positional drift. Alternative systems such as wireless follow focus (Preston FIZ, RT Motion) use identical focus gears with servo motors. For consumer lenses without focus gears, retrofitting is done via universal clamp-on systems or adhesive strips. Cine lenses (Zeiss CP.3, Cooke S4) feature integrated focus gears from the factory. For remote shooting and gimbal systems, lighter plastic focus gears with 40% less weight have become established.