This is a “rara avis”. The prototype version is named Zodiak -2 and was introduced in 1979, while the small series production was named Zodiak-2M-2. It’s a full-fledged M42 mount lens, on the heavy and large side. Like Zodiak and Zenitar lenses domes in his bucket with 3 rear mount filters, M28 x0.75 and the clear one is permanently on the lens. Recently raised on the auction websites surface and was gone for over 1200 eur (may 2023) Unfotrtunately it was not me.
Please do not mistake this with the RECTILINEAR 15mm f3.5, it’s called MIR-51, it’s another super rare lens, but has no fisheye projection.
Here the images, for sake of the knowledge. They are not mine. If you are the owner please contact me, I’d love to ask your permission and give proper credits.