Collapsible Elmar on Canon RF?
Here's an experiment with what I believe to be an Industar 22, which is supposed to be about the same size as the Elmar. The fact that is says "Taylor" on the front -- well, that's another story. The lens has a very crudely machined lip at the rear (most un-Leicalike), but it mounts acceptably on my Canon 7. (I haven't used it on the Canon but I did take some shots with it on a Leica IIIf this weekend and they were sharp and properly focussed.) Collapsing it is possible, but depending on the exact position to which the lens ir rotated, the rear lip may graze the light baffles or it may not. Even when it grazed the baffles, it seemed to do no harm, not even scratching them, but I wouldn't want to do it repeatedly. A writer on a Japanese site suggests gently reshaping the baffles with one's finger to mount a Jupiter 12 (another "problem lens" with the Canon) but I haven't wanted to do that to my Canon. The Industar (and therefore perhaps the Elmar) is a better fit than the Jupiter 12, but I don't think I'll be collapsing it on the Canon.
This is my LAST body!
(Agrajag, in Douglas Adams' Hitchhiker's Guide to the Galaxy)