Edit: photos of the issue here http://www.dropbox.com/gallery/19460365/1/PM90?h=854253 I just received a Hasselblad PM90 prism from a shop. It is generally in like new condition and the glass is clear and bright, however there is a white smudge mark running right across the middle of the prism. When you look through it, it is generally not visible (or very lightly when focusing at infinity), but I can see it if I try and focus on it. It falls right across the middle, horizontally, from edge to edge. If I look at the other end of the prism (the glass that sits above the focusing screen) I can clearly see a white line on the middle of the internal part of the prism. It looks like water/condensation marks that dried out...? Looking closer, it appears that at the edges it curves, just like condensation slowly clears from the edges in, so if it is on a square glass you get "rounded corners" as it clears towards the middle. Am I right in thinking it was probably dust that got stuck to the mirror when condensation formed in the prism and has dried like that? Somebody did a botched job trying to dry it perhaps? Or should I be worried that it is/will develop into fungus or something like that? Or is it the back of the prism/mirror ungluing itself...? I still have time to return it but it was a very good price, if the mark is unimportant and nothing sinister it is not in the way and, more importantly I need it and cannot wait till another one turns up at a good price, as I unfortunately smashed my other one. Any ideas? Thanks. PS In any case, for the future, can prisms generally be serviced and cleaned? Because if it is possible I'd rather keep it with the intention of getting it cleaned when I send the lot for a service next year, rather than ordering another one that arrives beat-up and dirty.