I picked up a Soviet-made Tair-3 300mm lens at a flea market recently, and I'm at a loss to identify what kind of mount it uses. According to what I've read,
most virtually all Tair-3s used M42 or T mounts, but this clearly isn't either of those.
The black bit with the orange dot on it rotates freely through about 90 degrees. I'm fairly certain it's an adapter, but I can't seem to get it to unscrew to find out for sure.
Apologies for the poor image quality - my phone camera's autofocus is utter garbage and I'm in a situation where I don't have a great deal of light available.