While putting everything away after the last session, I noticed that there was a little bit of wobble in the refractor focuser assembly. It was most pronounced in the left-to-right direction which corresponds to the DEC movement. I assumed this contributed to some of the DEC error I've been seeing in this particular setup.
Also, when I did the test with the C11, I was surprised at how well the mount handled the guiding. It was hovering between .6 and .8 total RMS error which is pretty good. While setting everything up, I noticed that when I rapped on the mount, there were vibrations felt for about 2-3 seconds. This is something that my AP900 mount does as well and it's really annoying.
Part of the problem is that the pier is a source of sympathetic vibration. Simply pushing my leg against the pier helps to dampen vibration. I've wanted to add a wooden disc in the middle of the pier so that it dampens the vibrations. I just haven't gotten around to it. :*/
But the vibrations are ALSO in the damn mount assembly itself! In the AP1200, I noticed that
the more I pushed on the saddle, the vibration seem less pronounced. So, as is the case with these sorts of things, I had an AHA moment: The AP1200 needs to carry more weight to dampen vibrations! The pic below shows how I cobbled together basically 6 lbs (my guess) of metal on the plate. I had to move the counterweight about a foot to balance things out.
After examining the focuser, I noticed that I could tighten some hex screws and reduce the focuser tube wobble by a lot.
When it got dark enough, I did my usual routine of Polemaster polar alignment. But when I did the PHD2 drift align, it reported an error of at least 7 arc minutes! Which is a lot.
I went through the PHD2 drift align routines and got it down to a more respectable amount. But I have to say that I often got some funky results using this method. In particular, the amount of error would vary a lot if I chose to drift align on a different star. So, my confidence in the drift align wasn't great. But after 30 minutes, it seemed I had reduced my polar alignment error by 65% ???
All this work was for naught... This is actually a screenshot from the previous night but it was actually generally better than I got on this night. With this setup, the best I seem to be able to do is about .7 total RMS error.
By 2 am, the error was consistently much higher.
I was pretty bummed. But I decided that after collecting 60 total 20 minutes subs of O3, I was done so I collected flats using the SGP flats wizard. I specified an ADU value of 25000 and shot away. I also collected 30 bias files and 3 darks. I need to shoot about 4 more hours of darks.
The thing I really need to do is try again with the AP900 from my backyard. That would confirm whether or not I'm really seeing error primarily from the mount or the atmosphere (or some combination thereof).
Also, I need to run the PEMPro polar alignment wizard. Apparently, that is the most accurate way to determine polar alignment. When I do that, I need to re-run the PEC training to see if I can make a better curve.
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