Is this fungus?

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.

No, fungus looks like a spidery growth. It look to be like a spot or two of balsam separation, where the cement between elements breaks down.

I doubt that such a small defect will have any effect at all on image quality.

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?

It does happen, but I wouldn't say it's common. I deal with hundreds of lenses in a year and only a handful have such a defect.

It can only get worse, but slowly I would expect.

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

It can affect any lens that uses cement.

Before you discount the lens though, try a small amount of lens cleaner on the front element, just in case it's just grease that's been stubborn. Apply the cleaner to a cloth, not to the glass, and use sparingly.

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.