Though I had serious doubts about its usefulness I didn’t want to pass up on the opportunity to get the Minolta RF Rokkor 500mm 1:8 mirror lens.
It came with almost all of its accessories, including the (tattered) leather case, 4 extra filters but unfortunately the filter wrench is missing. Upon closer inspection it looks like the main mirror is a little weathered but that doesn’t seem to affect imagery too much.
Image quality is surprisingly good, provided you manage to nail focus and hold the camera still c.q. use a sturdy tripod and head. I used it hand-held on a camera with image stabilization, the Sony A7R2, and could get away with 1/250s shutter speeds most of the time.
That last picture was one of the very few of a series that came out alright, most of the others were out of focus. I’ve found it extremely difficult to focus. I got best result by using the low magnification of the A7R2 and even while the image should be stabilized, the travel of the sensor isn’t adequate to cover for the image motion of my not to shaky hands so that the image jumps up and down in the viewfinder despite the image stabilization. Maybe you could put this lens to use after a lot of practice but I don’t think I’ll use it for actual shooting. And if you want smooth bokeh: looks elsewhere, this mirror lens provides the typical doughnut features in the out-of-focus regions.
Some more reading, including comments of others, can be found in this thread on TalkEmount.