Contaminated lens

[simsurace]

I found this contamination on the inside of the rear element of an Ai-s lens that I bought for a low price. It is very small and almost invisible unless backlit from a particular angle. Any ideas on what it is? Is it fungus? Anyway, I was able to remove the lens element and the contaminant came right off with a dab of alcohol. If it is fungus I will keep an eye on it and maybe clean it once more with peroxide.

[Roland Vink]

Fungus usually looks more like a network of fine threads running across the surface. These look more like water or oil spots which have dried up. Sometimes dust can settle on the lens, if the speck absorbs moisture it can be a starting point for fungus which could grow in this fashion, so it is better to treat it as if it were fungus just in case.

Hopefully Ric Haw replies, he has more experience with this than I do.

[Birna Rørslett]

As Roland states, these are droplets that have dried up, not fungus. If you can remove them with alcohol or other solutions, don't worry.

A lens that sees regular use (in daylight)  and is stored under dry conditions will rarely if ever develop a fungus issue. Fungus will be seen as bright spidery threads or diffuse spots.

[simsurace]

Thanks! Dried up droplets seem very plausible. Indeed, when I searched Google Images for pictures of lenses with fungus, I did not find any that resembled mine. So the lens should be ready to go!