Follow focus systems can be pretty expensive, between $100 to $1500 depending on features and quality of the build, but you don't even need to spend more than a few bucks to get yourself a decent tool. In this video, filmmaker Dave Knop (aka: knoptop) shows us how he turned a random $4 dollar keychain he got from a hardware store into a pretty effective follow focus that fits large and small lenses. Check it out below:

The keychain Knop uses in the video is called the Key Band-It, a flexible band made out of waterproof, latex-free material. Though these things are designed to keep your keys safe, particularly while you're at the gym, we can clearly see that it works well as a follow focus thanks to its accordion design and "ThermoPlastic Rubber" band, which provides plenty of grip. (You can get it for $4 at Lowes.)

Is it the greatest DIY follow focus ever? I don't know, but it definitely looks like it works. So it might be worth a shot, especially if you're not using anything right now to help you focus.

Source: knoptop