I bought this lens in a bidding duel on a Goodwill auction site ten years ago. .Probably paid $30 before shipping,. It arrived with the aperture blades stuck, but I found that if I warmed up the lens. the blades could move. The serial number said it was a Vivitar in OM mount made by Kiron.
Later, I took the lens apart and cleaned te aperture. There were no adjustments that I could see on the lens groups.
It's ten years later, and I realize I used this lens completely wrong, I ran around shooting it wide open and didn't like what I saw/ I should try again at a more reasonable f8, but there's no point to that. I have good M43 lenses
These were taken a while ago, all around f2.5 on M43 bodes, probably an EM5 and an EPL5.