Sent from my iPhone
FWIW--
I had similar experiences in trying to do astrophotography with a C11 HD Edge
on a Losmandy G11.
I finally concluded that there is too much mirror shift in the C11 HD Edge
and the G11 just is not good enough for serious astrophotography in the sense
that exposures longer than about 2 mins are almost certainly going to be
flawed, and maybe 15% of those under 2 mins might not suffer from
uncorrectable (high frequency) periodic error.
I'll note that there is a website (I forget where but you can Google the
topic here) that has a calculator that estimates atmospheric refraction
effects for different hour angles and declinations. The bottom line is that
if you are significantly off the meridian, unguided exposures - even under a
few minutes - will have a significant fraction of an arc-second refraction
which will result in egg-shaped stars. (On the meridian, stars move parallel
to the horizon with little refraction change.) Almost certainly, the effect
will be present if only guiding in RA and not DEC, so DEC guiding also needs
to be decent.
On the other hand, I've had some success with hyperstar since the focal ratio
is f/2 and exposures can be as short as 30-40 seconds - unguided. All of
which tells me long-focal length photography is not feasible/reliable with
the G11. Also, because I need to be portable, I find PoleMaster to be an
amazing tool for polar alignment. I now feel my greatest limitation is using
an older DSLR - a refreshing change from being exasperated by the mount.
Another advantage of using short exposures is that in a series of short
exposures, while refraction might impact the overall series, it produces a
small offset from one exposure to the next that will be removed during
stacking, and the individual photos will be pretty good. So my recommendation
is to try hyperstar.
PH