Any ideas on what this might have been for?

[Alaskan]

Anyone have a clue what this was for? It has marked on the side 150 meter focus and has fiber input. It doesn't work like a beam expander but does have an input lens inside which looks like a concave lens.

Large Beam Fiber Optic Collimator 80mm Daimeter x 160mm Length CTW Telescope | eBay

 

[Alaskan]

Being I don't have the original fiber or know the wavelength it was used it, it could have been just that except it has a focal point of 150 meters marked on it. Maybe it was operated in reverse as a coupling into fiber for some kind of IR link. Was hoping someone might recognize it.

 

[Cyparagon]

Any ideas on what this might have been for?

You read the title of the auction, right? I don't really understand your question. A collimator is just a convex lens (NOT concave)