Couple of days ago I decided it is a right time to do something about that, potentially very good mirror lens, as per this website:
http://www.strickling.net/russentonne.htm (have a look at attachment, it is not too bad for 45 sec, 16stack, 60D).
The problem is non-adequate fitting of the primary mirror, which is partly glued to a retaining ring, which is itself glued to the main tube, to prevent the ring from loosening. This glue looks like shellac, it is brown in colour and brittle.
In this particular case, the mirror is loose too much, so the system is showing a bit of astigmatism, but not always - depending on the direction the lens is pointed to.
Focus is also unstable, sometimes it is just lost after couple of minutes.
Has anyone managed to get rid of that glue and dismantle this or similar lens?
When I was doing this to my MTO-1000A, there was no glue.. only grab screws.
Obviously, this Rubinar is simplified version of it's older brother (MTO), and it is supposed to have even better resolution - but this is not the case here (not always, that is), because of a shabby mirror fixture.
I am thinking about heating the tube from outside, until the glue softens..