Welcome to APUG

It's a highly specialised lens for some kind of industrial use, it will be useless for conventional use. I have a 75mm f1.9 Dallmeyer that barely covers 35mm, mine's an oscilliscope lens. It's coatings indicate it's designed for something special, as you've indicated possibly thermal imaging.

I've quite a few adverts for Dallmeyer lenses but it's not listed. You'd need to look up lenses for thermal imaging.