White prism marks...?

[film_man]

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.

 

[paul ron]

I'm not familiar with yours, but prisms can be cleaned internally. Not all but some use a 2 piece system and the smudge you see may be between these parts.

Another problem in some old prisms is separation where compund glass was bonded. Yours doesn't sound like this.

Silver coming off in places foam is sitting on, like old Mamiya 645s is another very common problem but again not in your case.


.

 

[film_man]

Right, I managed to put up some photos of it here:
http://www.dropbox.com/gallery/19460365/1/PM90?h=854253

Actually, looking at the first photo there seems to be this residue all around the edges. The second photos is quite a magnified view of it.

The more I look at it the more it looks like some kind of residue? Bad servicing? Or glue deteriorating?

 

[paul ron]

Prisms are very easy to open yourself. Most just have a few screws holding the top case on, they are usually located at the corners near the base or along that rim, sometimes underneath the base. You may have to peel up some leather on some to find em but some double sided tape will put it back in place like new again.

using denatured alcohol to clean the surfaces, a can of air to blow the lint off and the deed is done. Just watch for the silvering I see deteriorating in your prism indicated by the straight white line in your image.

If the smudge is not effecting the pictures why bother?

 

[film_man]

Oh is that what it is? I'm not bothered about it and it doesn't even get in the way of focusing, my only worry was that it was some kind of fungus as I don't want it spreading to other bits in my camera bag. As it is not, I don't really care about it.

I'm a bit tempted to open it as there are 6 screws holding the whole thing together, but knowing me I'll probably end up leaving more dirt inside it...

What exactly is silvering? Is that the mirror surface deteriorating? If it can be repaired I might do it when I get the whole rig serviced sometime next year.

 

[Q.G.]

I'd leave it alone.
Looks like one of the vertices of the prism. They're never completely invisible.