I got this with a box of Retina-related stuff. It looks new. I've googled like mad but can't come up with a definitive answer. I'm really hoping it's a skylight filter because the skylight I have in 29.5, has some weird white junk growing around the edge of it, where the glass meets the mount.

EDIT: It reads: 042 T-filter f.K.-film

So ... can anyone tell me what this filter is for?

Is it a skylight? Or is it maybe a 085 for color film?

Any help is appreciated!