I have, probably the original, prism finder for my Mamiya RB. It's the bulky kind, not the metering kind or the more recent Prism II. As I understand it, Mamiya makes a magnifier that attaches to the eye port. I am NOT talking about the diopter lens. This is a flip up and down magnifier. I also heard, this magnifier attaches to the later version of this prism and that earlier version require a modification by Mamiya (which it no longer performs). What I do not know is, how I can tell an earlier version from the later version. Anyone know??