Ok, bought a 500mm mirror lens on eBay which has lots of "snowflake" marks on the mirror. Am I correct to assume this is fungus and can not be cleaned or repaired? If one would trya nd clean it, how wouldst one go about such a thing? Would such a thing be foolish?

These mirrors are surface silvered; so uncleanable IMO.

This stuff which is made for cleaning telescope mirrors, might be a possibility, http://www.dantronix.com/. I've not tried it though, and have no first-hand knowledge. There is a similar product in the UK called "opticlean" http://www.caliope.co.uk/.

Barry

Is the mirror currently sealed at the bottom of an optical tube assembly or is it free and clear of same?

J

Ok, bought a 500mm mirror lens on eBay which has lots of "snowflake" marks on the mirror. Am I correct to assume this is fungus and can not be cleaned or repaired? If one would trya nd clean it, how wouldst one go about such a thing? Would such a thing be foolish?

Is the mirror currently sealed at the bottom of an optical tube assembly or is it free and clear of same?

J

It's sealed in. The front of the lens has a clear glass piece which prevents direct access to the mirror unless it can be removed. The lens is a Tamron Adaptall SP 500mm.

This is probably beyond the abilities of most amateur repair people. You should consult a repair facility and try to get an estimate. If you have some digital photos of the mold/fungus, that would help in getting an estimate.

I asked Tamron USA. They replied that yes, it can be cleaned. The standard charge for lens work is $84 but they'd need to see it before they could give an accurate quote.

Is it worth doing? It's hard to tell if the lens is better than one of the current generation 500mm mirror lens sold under many brand names. Does anyone have a direct comparison?

I owned and used both Nikon and Canon 500mm mirror lenses. They were okay but the doughnuts finally got to me. I also owned a Tamron SP500, early 90s vintage, and I would rate mine at 8.5 if the C/N were pegged at 10, relatively speaking. I might add that there is definitely some sample to sample variation and if your unit has seen a bump or two there could be some alignment issues. However, if sent in for lens cleaning and repair, an alignment would be part of the procedure.

A follow-up post to let everyone know the end result. I sent the lens in to Tamron for evaluation and repair / cleaning. The estimate was $244. Obviously the lens isn't worth that, so I told them to keep it if it'd cost me anything to get it back. I can find another copy on eBay for $100 or less. It's not totally worthless (example shot below) but not a lens I'd use very often.

http://www.wolfeye.smugmug.com/photos/171788302-L.jpg