Autofocus is rarely used in professional film making because the focus mechanisms are not smooth enough to be adjusted while the camera is rolling. Instead, the focus ring on the lens is rotated manually using a geared hand controller called a follow focus. Sometimes the follow focus is turned by the camera operator and sometimes there is a dedicated member of the camera crew called a focus puller.
This Follow Focus Ring is a simple design to allow for easy focus or zoom controls while behind the camera. Reach arounds are nice and all, but can produce a less precise result compared to using a ring.
Inside diameter is 58mm, 60mm, 64mm, 68mm, and 72mm… held on with a simple rubber band. size does NOT need to be exact to fit your lens, I would error on larger. You can scale to any size lens to control Focus or Zoom or BOTH!
HINT: I have also heated one and compressed is slightly to fit tighter.
Let me know if you need a specific size and id be happy to design.