Yes, I'll try cleaning it again. Now that I'm satisfied it's not fungus, I've finally mounted it on my K5 and taken a few test shots and so far I'm pleased with the results. Although I'm still a little worried about the long-term significance of the spot, I'm also quite reluctant to return the lens to the seller (if he'll take it back) for something that may yet turn out to be trivial. Decisions, decisions!

Thanks again for all your help.

Regards, Noah.

Thanks, John. I forgot to say that it's a fairly modern lens - fa 35mm f2. Does balsam separation also affect modern lenses?

John, thanks a lot for your quick response. I must admit I haven't even mounted the lens on my camera yet to test it, as I was worried about the potential fungus spreading to the rest of my equipment! As you say, I'm sure it won't affect the image quality as it is now - but is the balsam separation something that is likely to spread, or is it fairly common to have random specks like this?

Hello, I'd be very grateful for your help with this. I bought this lens on Ebay; it was described as being in 'excellent condition', but when I received it I was surprised to find that the front was very dirty, and had numerous marks and splodges on the surface. However, after a careful clean, most of these have come off - but not the one in the picture (there are also various grime marks around the very perimeter, but I'm less worried about these). It looks like a shiny, silvery spot, is very small and can only be seen at certain angles. When shining a torch through the lens I haven't been able to see it. To the naked eye it looks hard-edged, but in this close-up shot the edges look more ragged. I spent hours yesterday looking for pictures of fungus spores, but I still can't decide if this is fungus or not.

I'd be very grateful for your opinions.

It's not glass, but I can recommend this one:

http://www.amazon.co.uk/gp/product/B005CO8QD2/ref=oh_details_o01_s00_i00

It's easy to install, fits perfectly, and you have to look very closely to even notice it's there.

Dave & Carl, have you experienced any Newton's Rings with the Acmaxx? I opted against this protector as there were reports in various forums about people experiencing a 'rainbow effect'.