Very good purchase, and good price/performance for those russian lenses !
I have all 3 of them (Rubinar 500, Rubinar1000 and MTO-1100A).
The best of the lot (from the image point of view) is MTO, and I am using it as a main scope for imaging (and for spectroscopy in the near future).
See here:
http://www.iceinspace.com.au/forum/s...&highlight=MTO
http://www.iceinspace.com.au/forum/s...&highlight=MTO
http://www.iceinspace.com.au/forum/s...&highlight=MTO
However, I needed to do a slight modification to it's optics, according to the link below (to remove the astigmatism of the main mirror, I relaxed the uneven pressure on glass by adding 3 contact pads on the mirror rim, aligning pads on retaining ring with those and reducing the mirror retaining ring pressure by screwing it on only lightly, and
without grab screw at the side. Relaxing the retaining rings of the correction system did not improve the image, due to the glass thickness (as pointed out by Wavytone, there is a lot of thick glass there - perhaps this is the reason for 50% transmission, glass appears to be a bit yellowish ? ). This significantly improved the image quality (VERY visible on individual star images).
Another big improvement was achieved by the way the lens tube is mounted (again, there is a hint on that on Strickling's website
(http://www.strickling.net/russentonne.htm), and here:
http://www.harpoint-observatory.com/...ussentonne.pdf).
And, of course, you need to allow the whole system to be in thermal equilibrium - any temperature differences will significantly deteriorate the image quality .
I still need to do the same thing on Rubinar 500 and Rubinar 1000 (a bit tricky because the retaining rings are glued with shellac or something similar, I am not sure how to remove it without damaging the mirror).
Interestingly, corrector plates on those two lenses are much thinner.
Attached image of Tarantula is done last week with MTO-1100A and Canon 60D (stack 12x 45sec ISO3200).