<p>Hi Stephen, thanks a lot for your input. Let me try to answer your questions. The Visoflex is mounting directly onto the camera body, no extension rings or anything. You are right, my Visoflex has an interchangeable focusing screen, I did not know there was another type of Viso... I have checked a lot of pictures, and it is obvious in your picture, that my focussing screen is different, mine is totally transparent. However, since the image forms perfectly well on the prism, in sharp focus, it seems the problem should be on the mounting as you mention, but the Viso mounts well and I don't see any difference with other Visos, nor can I find the screws you mention. Here are some more pictures of my item.</p>