Thanks, redpit, for your in-depth story about this lens. I actually like mirror lenses very much, and your photo's show exactly why. In certain situations they simply outperform traditional tele-photo and long lenses. While many people consider the donut bokeh to be unattractive, in certain situations it can create very artistic images, which are very pleasing to the eye. My first mirror lens was a 600mm sigma. It had very poor image quality, but was fun to use. I sold it and purchased a Soviet 3M-6A 6.3/500mm, manufactured in 1984 at the Lytkarino factory. It simply blew away the sigma. But, just like fast car entheusiasts, I need more power! I've tried using this lens with a doubler, but the results were less than satisfactory. I am looking into getting the MTO-1000, thanks to your report. I also enjoy shooting with old lenses, as in many aspects they are far superior to modern lenses, and while they can be a bit unweilding, they are fun to play with. I have found, through experience, that the older Soviet lenses manufactured by KMZ often have superior optics, especially those marked with the red P (it looks like an upside down U in English letters). Finding one in good condition is the real problem, since they are so old and usually well used.I have several of these lenses, from the late 1950's and early 1960's, and I love the images they render. I have also read that the models with "00" at the beginning of the serial number are also superior. I have owned about twenty or so Soviet lenses of various design, and this always seems to hold true. Apparently, each lens is tested in the factory, and the ones which had the best results were set aside for dignitaries, and military use, and marked with the "00." The one's marked with "000" were prototypes and should be avoided if you plan on using them. They are quite prevalent on the used market, and often in near new condition. These lenses often have improper coatings, or other anomalies, which is why they weren't sold. The rest of the lenses to be sold are marked first with the year of manufacture. So, for example, if the serial number started with "84," it was manufactured in 1984. Someday, I plan on writing a full article on these fantastic lenses so all of us Pentax Forums members can see how well these lenses work with our wonderful cameras. I have a Pentax K5IIs, and I recommend it highly, as the 16MP sensor is a fantastic one, and not having the AA filter helps it take significantly sharper images than the K5. If you like shooting manual, like I do, it is all you need, and can be had for a song these days. In closing, I am posting an image I took of last year's blood moon with my K5IIs and the Soviet 3M-6A, and an aftermarket doubler. I used a heavy tripod, a remote trigger, and shot with the mirror up. The atmospheric conditions were not ideal, but I was still somewhat pleased with the results. It's still not sharp enough for me, most likely due to the atmspheric conditions, the doubler, and the cropping.
