Tokina 17mm F3.5 AT-X 17 AF - Fungus?

Hi everyone. I need some help please.

I bought this lens today and while it is in otherwise perfect condition, I can't tell if these marks on the very final element at the back are just some manufacturing scratches on the glass or if it is fungus?

It doesn't seem to affect the image quality.

Photo taken with a 70mm Macro, full res link below.

https://ibb.co/jrpDYNG



Edited by Neildlr - 06 March 2023 at 17:11

Looks like fungus to me. Lens element easily removes as I see a slotted holding ring. Perhaps you can clean, but if you can return with refund you avoid disappointment when you can't clean. If you leave it it may grow until you cannot use the lens anymore.

I tried to clean it with a lens pen first, then tried a very lightly damp cloth that I carefully pushed with a plastic toothpick. None of that worked.

Then I carefully felt it using the toothpick and it actually feels like the glass has been sanded or scuffed?

I guess so. Its the first time I've ever seen this on a vintage lens (in the ones I've physically come across) so its just a bit odd.

I'll see if it gets larger or anything and then i guess we'll know.

I have seen reports that fungus can leave marks on the coatings even after being cleaned so maybe this lens has had fungus in the past?

Instead of illuminating the lens from the front, it's better to hold up a flashlight thru the back of the lens and take a picture with the exact element in focus.
Fungus leaves telltale lines and dots and when you flash a light thru the back of the lens, it can show up as tendrils.
It's quite normal that the pictures with the lens might be fine. The fungus could stay that way for years without growing, if it is fungus.
But since it's a recent purchase, you might want to return it just to make sure you didn't pay market price for what could turn out to be a dud.
Regards
Sashi