What is this?

[Mjd-djm]

I've seen this quite a few times before in lenses and have been meaning to ask. It appears to be marks on the metal components inside the lens, but not exacty sure. Anyone with better knowledge than I care to chime in?

 

[Greyscale]

Schneideritis.

https://www.photrio.com/forum/threads/what-is-schneideritis.18363/

 

[benmacphoto]

Looks like the black paint that is used around optics to prevent flare and reflections is deteriorating.

 

[Arbitrarium]

What benmacphoto said. I had this on an LTM Canon 50mm 1.4. Luckily they're stupid easy to disassemble and I just repainted it with a gun metal touch up pen.