boris-

I don't think so. The lens has been in his box in a cabinet with other photographic equipment. I don't think I bought it like this 15 years ago, but who knows...

I would like to sell it just because I never use it.

Here are some quick photos. They are taken with a Fujifilm XT3 and a Nikon to Fuji adapter. This lens was never very sharp. I bought it used like 15 years ago. I think this stain was not present, I guess I would have seen it. Recently I compared it to an old manual Nikon 200 mm to make a video shot with my Fuji XT3. And the Nikon was much sharper and contrasty and it showed much better colors. The image of the Sigma was also greenish. But that could be the case even if the Sigma was in perfect condition. So I don’t know how much this “separation” is affecting the image.

Hello. Thank you for the comments. I am sorry for taking so long. So, it could be about about separation. Here are other photos: So basically, repairing this separation is very expensive and it is not worth the money considering the lens, right? Anyway, I could ask a lens repair service in my city. And does this separation progress gradually or it always stays like this?

What is it? Could it be cleaned? Does it affect the image?