Foton F-ring focus ring FRG12 (focus lever for DSLR or camcorder, diameter 70-75 mm) (Electronics)
The ring should not be fastened too tightly against the Zoom or Focus Ring. Otherwise, the mechanism is possibly stiff. Sits the ring is not tight enough, he slips through. Possible solution: Den or the lens rings with Lasso tape, etc. thus wrapping