I want to do some moon photography and thought a 500mm mirror lens might be the cats whiskers. Years ago I had used a Nikkor 500mm lens for newspaper work and it was tack sharp. On APUG.org there was a Vivitar 500mm mirror lens for sale at a reasonable price so I bought it. I was under no illusions that it would equal the Nikkor but hey I might get a good one. It arrived, I put in on my Panasonic GX7 and set it atop the Manfrotto tripod that I use for 4x5 photography. To insure I didn't suffer from the dreaded shutter bounce, which BTW I have never experienced, I set the camera to electronic shutter. Also set it to delay timer of 2 secs to further reduce any stray vibrations. Well the results were less than stellar to say the least. I thought maybe a long focal length like this just doesn't work with the GX7 so I put my wife's 400mm Canon FD f4.5 SSC lens on the camera and repeated the test. The Canon lens was crystal clear and sharp. So I guess I will be selling the 500mm lens to someone who wants a nice dreamy look with funky doughnut highlights. Any takers lol.