I removed/unscrewed the spiral for projection use which reveals a 50mm thread, then its a 52-50 step down ring then into a helicoid which you can buy here
Then just add some M42 extension tubes depending on the camera, for mirrorless you will need size 1 + 2.
The tripod mount ring is padded with some rubber strips cut from a sheet so its nice and sturdy.for this 4 inch front optic
This lens is part of a family which mount the same way, the set is
1 ISCO Ultra AV F3.5 200-300mm purchased in England for £20
2 ISCO Cinelux AV F3.5 110-200mm purchased in Germany for €14
3 ISCO AV F3.5 60-110mm purchased in US for $11
so the helicoid gets a lot of use as well as for other lenses....
The lenses suffer from PF in high contrast areas which is easy to remove in post, see the 1:1 pixel below. The image is pretty good at 1080p
