Opteka FF180 Reversible Follow Focus with 10" Whip and Speed Crank for Digital SLR and Video Cameras Completely gear-driven design for slip-free, accurate, and repeatable focus movement 1:1 gear ratio allows smooth movements for still and motion picture 35mm lenses Adjustable slide-mounting mechanism to fit large range of lens diameters, including video camera lenses Industry-standard 15mm lightweight (60mm spacing) rod mount Gear drive can be mounted from both sides for left or right hand use