Thanks for commenting -- you posted:
Did you do guided tests? At such focal length and mirror you need to guide OAG, to do unguided at such a focal length with mirrors you need elaborated modelling that 10Micron, PM and some other high end mounts offer. Anyway I would never ever expect the E.fric to do unguided imaging at such focal length with mirrors that is just not realistic. If you guided and were not seeing good results that's another story ...
Yes, it's another story.
Running unguided (in my case) was only a short test, to see if the
guide star would stay relatively stable. I was not even collecting
an image on the imaging camera at this point, just watching the
guide camera images and looking at the guide output. (It is
possible to run the guiding software without generating guide
pulses, just to observe the behavior.)
I am quite aware of the demands of longer focal length, and of
higher payload weight, having dealt with both for several years.
That's why I purchased the E.fric, and why I am lightly
cautioning people who may have higher-weight payloads than
yours, that may approach the photographic specification of the
mount, until I can do a little more testing.
By the way, you mention the "mirror" -- often when people see
the designation "Cassegrain", they think "Schmidt-Cassegrain",
then they think of a commercial Schmidt-Cassegrain like a
Celestron that has a moving primary.
My telescope is a Cassegrain (most OTAs with a centrally-perforated
primary are), but in this case, it is a truss Harmer-Wynne, with a
"fixed" primary. I put "fixed" in quotes, because it is alignable
(capable of being adjusted for "collimation"), so it does of course
have adjusting screws, which are suitably tightened in order to
prevent the sort of problem I am seeing. And you are correct,
mirror telescopes in general, no matter how constructed, are
often collections of moving parts.
Guiding tests somewhat check the guiding mechanism as well,
but my actual *guiding* has been pretty good. That is to say,
the guider tries to compensate for the jumps taken by the guide
star. I incorporated a suggestion by Andras to reduce the guide
speed and lengthen the guide pulse. So, I am guiding and not
seeing the results I was hoping for, because of unexplained (i.e.,
not related to seeing) movement of the guide star on the guide
camera sensor. Since this can have several causes, I am trying
to eliminate them before coming to any conclusions.
As you know, that could take days or weeks! I already have
a few of each put into divining the problem.