Submitted by one of our readers in the comments section [Thanks Jerry]. Here's an interesting video on a DIY Lego follow focus from YouTube member havok2. Small, Lightweight and stable. It is attached directly to the lens, and variable sizing helps to adjust for other lenses. Taking it even further, there's a complete 3D Rendered video tutorial on how to put everything together. Additional photos can be found via slideshow https://slideshow.havok2.imageloop.com/en/index.htm. To help you get a better idea, you can check out the video description, questions, and additional comments at the video page.
3D Rendered Build Video