The Tokina AT-X 12-28 PRO DX has a super-wide to semi-standard zoom angle as versatile photography. We gave a follow focus gear on such lens to make suitable videography more by DSLR.
Follow focus works effectively by making a focus ring having a clutch system on MF. The feel when manually focusing has moderate sense of torque in the focus ring, enabling precise focusing.
AF/MF switching is accomplished by the simply sliding focus clutch ring forward and back on the lens barrel. When photographing normally (taking photos), auto-focus can be used.