[mauvehaus]

This is a thing in vintage lenses:

https://camerapedia.fandom.com/wiki/Radioactive_lenses

I own a Super-Multi-Coated Takumar 50mm f/1.4 and can confirm that the glass browns with age. UV exposure (sunlight) does clear it some.

[dheera]

Yep, I have a couple thoriated lenses, it sucks that people downvote an actually relevant comment without understanding.