One hassle with dSLR video is having to attach follow focus rings to your lenses, often with a clunky bracket or closure to hold them in place. From my experience, these brackets frequently get in the way or have to be adjusted around the lens as your change focusing distance significantly. Now, perhaps inconvenience is your thing, but, personally, I find it annoying.
The ring is essentially a piece of toothed rubber with sizing notches where you can cut it. Once properly sized, the ring is held together by pins, which looks similar to the way linked watch bands or fashioned together.
The advantage is that these rings provide uninhibited, full 360-degree rotation of your focus ring. No more adjusting, not more cursing the names of Nordic deities in the middle of shoot, drawing weird stares and worried expressions from those around you…less time spent in anger management therapy… (The benefits are quite good, if you ask me.) According to Cinegears, who may or may not be suffering from inflated egos, these are “the best solid rubber focus ring attachment” that money can buy.
You can pick them up from their website for $35. This price, however, is for a single ring…that you will cut down to a single size. The drawback comes from the cost vs. flexibility argument, which basically means you will be paying $35 for a single piece of rubber. More cost-effective (albeit, less convenient) alternatives can be found on Amazon, such as $6.99 for an adjustable focus ring or $25.99 for a set of three pre-sized focus rings (unfortunately, with brackets).
But, if convenience is your ultimate goal (personally, mine is not killing anyone before I die), then give it a go!