Recently I did my first lens modification on a helios 44-2...nervous as I have never unscrewed a lens before...watched a few YouTube videos and took it slowly and I think it worked okay...just the front lens...After hours of trying different things such as a helicoid, lens extender ,extension tubes and a few variations of putting them together I found the 16mm extension tube to be the best so far to get a reasonable focus...handheld but will try with my camera on my tripod tomorrow....here are 3 results that I am quite happy with...shot on my Sony nex 7 camera with an M42 adapter...
Here is the link to the video I liked to show you how to do the modification....
https://youtu.be/EPTPxCGNHkI