Celestron 6SE with Nexstar alt/az mount + PHD2

[Roland Teague]

Hello all, after having some good success with doing EAA with my Celestron 6SE + Hyperstar with 30 sec subs over the past 6 months I have decided up my game with a relatively inexpensive Svbony 30mm guiding scope and sv305 camera in order to try to get 60 or even 90 sec subs. Camera (and scope) are working just fine with PHD2. But, I am having issues Calibrating the Nexstar alt/az mount with it complaining that the Dec Backlash not being within toleration. It recommended that I lower the Dec backlash on the scope so I have tried changing the backlash from the default of 15 down to 5. I also tried 0 but that seem to seemed to make things worse. I was finally able to get a Calibration within tolerance with a setting of 5 but it started having guiding issues within 10 minutes (long trailing star streaks) with Dec backlash issues. I was taking 60 sec with this test.  I also ran the Guiding Assistant and applied the recommendations.

I have attached screenshots of my Advanced Settings, Calibration Calculator, algorithms, and calibration data. I had lowered the guide speed to 0.5 in this test.

Looking some help to troubleshoot the issue as PHD2 is a bear to work with at first.

Link to PHD2 logs.

https://openphdguidi...2_logs_c8PY.zip

[Roland Teague]

Log link got munged for some reason.

https://openphdguiding.org/logs/dl/PHD2_logs_c8PY.zip

[Roland Teague]

So I installed the PHD2 log viewer and wanted to provide some more info for the best events to look at in the logs. The calibration and guiding events that I looked at were on 2025-03-02 22:34 - 22:48 roughly.   I also want to point out that I am NOT using a wedge just in case that wasn't clear. I'm also not expecting miracles with an alt/az mount but was hoping to get guiding to work to allow for 60 sec subs. I am not expecting to be able to get 5 min subs with this mount like you would get with a typical EQ mount.  Does anyone have experience using a standard Nexstar mount with PHD2?  Should I enable the backlash compensation in PHD2?

[Bruce Waddington]

This is probably not the forum for getting help with this because everything we do with PHD2 - including support - is based on the premise that RA is RA and Dec is Dec.  The best I can offer is to point you in this direction:

https://telescopemount.org/guiding-the-panther-alt-az-mount-with-phd2/

You may be able to get help from the author or by reading other material he has on his web site.

Bruce

[Roland Teague]

Hi Bruce, thanks for the response. So, I believe you are telling me that PHD2 was never really designed to work with alt/az mounts if I am understanding your message correctly.

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[Brian Valente]

Hi Roland

>>>>I believe you are telling me that PHD2 was never really designed to work with alt/az mounts if I am understanding your message correctly.

You are correct that the two were not intended to work together, but I would more accurately say alt az mounts are not really designed for long exposures that include guiding, since alt az mounts introduce field rotation (there are workaround re: field rotator but my point is generally)

Brian

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Bruce Waddington]

Yes, it's a use-case we don't want to spend time on.  It's inherently limited and poses a bunch of diagnostic problems that are very time-consuming to figure out.  If you have any serious interest in pushing ahead with deep sky imaging, you need to get a proper equatorial mount or experiment with lucky imaging on the brighter objects.  Otherwise, you're just going to waste your time fighting with a bunch of unnecessary problems.

Good luck,

Bruce

[Roland Teague]

Yea, that is a bummer. I'm actually getting good results with 30 second exposures with my Hyperstar. You can't beat that fast glass. An EQ mount is just not in the budget right now because of the cost.

Brian, I knew that the field rotation was going to limit my exposure time to a max of 60 sec or maybe 90 sec with an alt-az mount but the more I think about it, over the course of the night, I can imagine that the field rotation would cause issues with the guiding.

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