A bumped focus ring ruined too many astrophotography exposures so I created this-slip on lock and micro adjuster for the Canon 200mm F2.8 L USM II lens.
It really works. I tested it taking that image of Comet Catalina.
I left some room for velcro loops to pad the lens barrel.
You also need 1/4 20 threaded rod, two lock nuts and a furniture slot nut.
FolgerTech Kit, Kossel Delta 2020
Could probably use some supports in the fixed ring part.