Is this fungus?

[fuzzywuzzy]

I recently got a Schneider-Kreuznach Durst Componon 150/5.6 bundled with some other things. I don't know what mount it originally had, but now it's got a M42 thread glued onto the back. It also has a big ol' blemish of some kind on the inside of the rear element.

It doesn't have the fibres/threads I'd expect to see, and it's very shiny in the right light, I'd almost think it was a chip in the glass but the edges are sort of rounded?



Very shiny when the right catches it at certain angles



taken with bellows Tak 100/4 at full bellows extension, 100% crop



The lens is pretty unwieldy on a SLR, the bellows needs to be extended about halfway for the thing to reach infinity

The pictures have nice colours but are a little soft, no surprise with that shiny blob on the rear element.

[Drack]

To me it looks like someone has spilled glue , grease , paint or something similar. I don`t think that it`s fungus trough. Try using a micro fabric cloth and some cleaner or alcohol to wipe it off.

[GrahamNR17]

Could it be an odd creeping shape of an air bubble between two bonded elements? certainly looks very curious, and not at all fungus-like.

[Attila]

Not fungus for sure.

[fuzzywuzzy]

[Smoli4]

if its indeed separation, i would be glad to take a look ofc in case that you would like it fixed or it impact image contrast etc..