The Cavision RFGR80 is a gear ring that can be clamped onto a focus ring, allowing for the use of a follow focus system. It is specifically designed for lenses between 78mm and 81mm.
Note:
For DSLR lenses, the focus barrel size does not correspond to the filter thread size. Please measure the diameter (or circumference divided by 3.14) of the lens's focus barrel to determine the correct gear ring.