PHD Guiding Tips

[boz_m (Alexander)]

Hi all,

I have been recently trying to get my guiding better. I have a Celestron 8" EdgeHD + 0.7x reducer and an AVX mount.

This is my startup routine:
- Run the AVX two star align + 4 calib stars
- Run the AVX polar align
- Open PHD2 and run the calibration routine
- Run the PHD2 drift align (but the AVX polar align did the trick this time)
- Run the PHD2 guiding assistant to work out the best settings

This is the first time i have done this and my guiding improved a lot. I was consistently under 1 RMS error.

3 questions:
- The first picture is my backlash graph from the Guiding Assistant routine. Does this look right?
- The first guiding graph is around the zenith. When i was doing this i was getting 6 min exposures with no star trails. The second graph was near the polar star. The graph looks better, with lower error, but each time i tried to do a 6 min exposure i was getting noticeable star trails. Why is this and how do i remove this error?
- Any tips on my guiding based on the graphs in general?

Any tips appreciated.
Cheers, Boz.

[Imme (Jon)]

I would go longer exposures....much longer.
1 second and you’re chasing seeing. Try 5

[boz_m (Alexander)]

Thanks imme. Will try longer guide exposures.

Btw I think the issue with bad guiding at the pole is differential flex ire in the guide scope. I had a look and it wasn’t secured fantastically and was probably shifting slightly when I changed position in the sky. Will tighten it all up and give it another whirl tonight.

[kens (Ken)]

In case you haven't already found it, here's the PHD2 Best Practices document:
https://openphdguiding.org/PHD2_BestPractices.pdf

Guiding VERY close to the pole is interesting. On the one hand there is almost no periodic error in RA but the RA and Dec corrections are almost parallel. You also can get significant field rotation. On the few occasions I've done it I disable RA corrections and make sure your PA is spot on to prevent field rotation. This calculator helps work out how good your PA needs to be. http://celestialwonders.com/tools/ro...ErrorCalc.html