Follow focus

These gears feed to a wheel that, when turned by a focus puller, spins the teeth and thus the ring on the lens.

However, this would place the hand in an awkward position perpendicular to the camera rather than parallel, and turning beyond a certain distance (such as 360 degrees) would be impossible.

A focus puller often uses a tape to correctly measure the distance from the lens to the subject, allowing for accurate marking of the disk.

Such lenses are sometimes called "focus by wire," and the behavior then depends upon the software algorithm used by the lens.

However, certain implementations of such a system also consider the speed with which the ring was turned (called nonlinear focus-by-wire), which can make precise and repeatable focus pulls difficult, and use of a follow focus impractical.