These https://www.reddit.com/r/TrueCinematography/comments/flu6y1/barry_lyndon_for_poor_people_zeiss_biotar_100mm/ i think they are used on old x-ray scanners and had to be super fast so that the exposure to x-ray radiation is minimal :D i'm sure Russia has an answer to zeiss on this one but i havn't researched it yet .
On the helios topic i have the 44-4m (my first manual lens i tried on digital aswell as part of my firs film camera kit the zenit et -that i love) and currently it has it's front element reversed - maybe i'll do a post on how it looks. I hate when people underestimate russian made optics. The industar 50u i've never tried but ill check it out for sure