Hello everyone,

I’m looking for some advice regarding a recent imaging session on NGC 7023 (Iris Nebula).

Equipment:

  • Sky-Watcher 150/750 with focal reducer (~375 mm focal length)

  • ASI662MC camera

  • EQ5 Pro mount with EQMOD

  • NINA + PHD2

During my last session, guiding appeared to be good:

  • RMS generally between 0.15” and 0.40”

  • PHD2 calibration completed successfully

  • Dithering was working properly

However, I noticed two issues:

  1. The target gradually drifted across the frame throughout the night. Between the first and last image, NGC 7023 shifted by several hundred pixels even though guiding remained active.

  2. After analyzing my data in PixInsight, out of 100 exposures of 180 seconds, only 25 were considered usable. A large number of the rejected frames appear to have elongated stars.

I also noticed recurring DEC spikes in PHD2: a large correction in one direction followed by a similar correction in the opposite direction a few minutes later. This looks like backlash or some kind of mechanical issue on the DEC axis.

What do you think is the most likely cause of these symptoms? DEC backlash, poor worm gear adjustment, a PHD2 calibration issue, differential flexure, polar alignment error, or something else that I may have overlooked?

I’ve attached a few screenshots showing the calibration results, and the drift between the first and the last frames

Thanks in advance for any advice or suggestions.📷 IMG_0747.jpegIMG_0747.jpeg📷 IMG_0748.jpegIMG_0748.jpeg.📷 4DE14CE9-56FA-48CD-BC3A-97809CDEAFF8.jpeg