Hello wetpixel,
here is my first contribution: I made a 3D file to have a zoom gear for my Panasonic 12-30mm lens !
That is for a Nauticam housing (i have a NA-GH3/GH4).
If you have a 3D printer or know someone with one, it's a good way to save money over buying from Nauticam.
Please like & download / comments on https://www.thingiverse.com/thing:2811239
Éric