Simon, I know this post is super old and you'll most likely not respond but, I just purchased an Eymax 50.8mm (2in) f/2.8 and it has that focusing ring screwed onto it and it allows the lens, obviously, to be mounted into my Eyemo. How do you set the distance with that? Is it a slight unscrewing of the lens (once mounted) so that the distance markings work accurately?