M44 and Equipment Tuning

My objectives for this session were to work on focus and guiding. I had not planned to try to image anything, but I decided to do a quick capture on M44 after I was through.

For focusing, I wanted to do some checks to verify that I had overcome the issues that I had last session. The issues and solutions were:

Focuser position was decreased by more that 100 steps after each refocus. I suspected a loose clutch, which I tightened as tightly as I could. I was still getting positions that were decreased by about 2 steps after each focus.

The guide camera was set parfocal with the guide camera while the L filter was in front of the main camera. When the R filter was rotated in and the main camera was refocused, the PHS guide star profile FWHM went from pretty good to really bad. The same happened when the main camera was refocused on the G and B cameras. I suspected that the focuser positions for the L and RGB filters were different, so I wanted to check that out during this session.

It turned out I had replaced the mounted filter that came with ZWO set with an unmounted filter to see if the unmounted filter would create less vignetting, and it does not help much. I checked the ZWO L filter against the Astronomik filter and found that the focuser position was about 80 steps different between the two L filters. I will be using the ZWO L filter going forward.

I focused the main camera with the ZWO L filter in the train, and co-focused the guide camera. I then ran the RGB filters through the path with an autofocus run after each filter change. The PHD guide star FWHM did not change significantly.

Next I moved to experimenting with the PHD P-PEC, min-move, and aggressiveness settings.  With P-PEC, I couldn’t get the Ra RMS less than about .9, which was more than 2x the Dec RMS, so I went back to Hysteresis. I played with min-move, and only seemed to make things worse. I did a GA run, and accepted the min-move recommendations and guiding got better, but not as good as it was for Monkey Head on the Ra axis. I increased the aggressiveness a couple of times and guiding improved.

I had not intended to shoot a target for this session, but with guiding going well, I could not resist a quick capture. On M44, I shot 12 RGB frames at 60s each.

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