stephen_mcateer Posted April 5 Share Posted April 5 (edited) I'm looking at a Mamiya prism on eBay. The prism looks to have suffered some sort of degradation but I'm not sure what kind. [See pic.] Just wondering if I could dismantle it and clean it? Thanks for any advice. Edited April 5 by stephen_mcateer Typo Link to comment Share on other sites More sharing options...
John Seaman Posted April 5 Share Posted April 5 Never seen anything like that, it looks like impact damage. I very much doubt if it could be cleaned off, although it probably won't affect operation. Are you sure it is a prism rather than a pentamirror? My first reaction was that it had been invaded by ghost spiders from Mars (sorry). Link to comment Share on other sites More sharing options...
stephen_mcateer Posted April 7 Author Share Posted April 7 @John Seaman Thanks John. I decided to pass on this one as it looks to be beyond repair. (I see another on elsewhere that I may bid on though...) Link to comment Share on other sites More sharing options...
orsetto Posted April 8 Share Posted April 8 It does look like impact damage, tho I wouldn't expect to see such extensive cracking along all edges of an actual solid glass prism. Agree with John_Seaman that this might be the cheaper "Porro Finder" that used a set of fragile flat mirrors vs a solid prism. The Mamiya porro finders can often be found more easily and for less money than the true prism, but the viewing image is much smaller and dimmer (fine for outdoor and landscape, not great for indoor where the WLF or true prism show a larger brighter easier-focusing image). IIRC, the porro finders were offered only for the Mamiya TLR cameras, not the RB/RZ67 or 645 series. The porro option is more effective for the top heavy TLRs anyway: much lighter than the true prism, and you can get a porro version with built in TTL CdS meter. The true solid glass Mamiya TLR prism is more compact than either porro, but weighs much more and is not available with TTL meter. Link to comment Share on other sites More sharing options...
stephen_mcateer Posted April 10 Author Share Posted April 10 @orsetto Thanks for that information. I decided to pass on this finder, and instead bought a Mamiya 330 F in poor condition, but which was bundled with a prism in nice condition. [I re-sold the 330 F the following day.] So I now have a proper prism finder for my 330 Pro. The cost, all-told, was very reasonable. I saw lots of Porro finders, which are much cheaper but I did some research and found out what you describe here: the image is smaller and dimmer than the prism. Cheers. Link to comment Share on other sites More sharing options...
c_watson1 Posted April 12 Share Posted April 12 Tough to say which came first: desilvering or impact. Junk now whatever the cause. 1 Link to comment Share on other sites More sharing options...
hjoseph7 Posted April 16 Share Posted April 16 It looks like it was pressed against a hard object and the pressure cracked the glass... 1 Link to comment Share on other sites More sharing options...
stephen_mcateer Posted April 18 Author Share Posted April 18 On 4/16/2024 at 2:53 PM, hjoseph7 said: It looks like it was pressed against a hard object and the pressure cracked the glass... I think the vendor said it had come out of a storage unit, so anything's possible. Link to comment Share on other sites More sharing options...
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