This is an Arsat 80mm f/2.8 medium format lens with a Pentacon Six mount. It's relatively inexpensive and can be found on eBay on most days. Got mine as a pair, along with a Carl Zeiss Flektogon 50mm f/4 from a seller on eBay.
- Lens elements: 6
- Focal length: 80mm
- Focusing scale: 0.6m to infinity
- Minimum focusing distance: 0.6m
- Aperture scale: f2.8/4/5.6/8/11/16/22
In actual use on the tilt adapter, it is a little soft at maximum aperture as expected, but gets sharper at f/4 and beyond. I don't mind a little softness wide open as I like the look and fits my visual style. I believe the version I have is single-coated (as denoted by the C next to the name ARSAT); the newer version has MC written on the ring (multi-coating) from the pictures I've seen on various sites.
Obviously, I can't compare this lens to the Nikon or Canon tilt/shift offerings (as those are beyond what I can afford to experiment with), but I can't complain about the lens build or image quality considering what I paid for the lens.
For more information about this lens and test results, check out the following sites: