Checking Sidereal Tracking Mount Accuracy

[niteman1946]

Hi Group,

My gear consists of a permanently mounted CEM120 (non encoded) with a Classic 12" LX200 (de-forked) SCT.  Effective focal length with reducer is 2180mm.

 I use SGPro for my automation.

During SGPro's auto focus routine (2sec exposure and 9 data points) guiding is off, and I see the displayed star field move slightly in the RA direction with each exposure.  By the time the 9 data points process is complete, the guide star (previously selected by PHD2) has moved substantially away from the PHD2 Search Region, and guiding usually fails.

I've increased the size from 15pxl (default) to 30pxl and that has improved, but not eliminated, the problem.

I'm probably wrong in my conclusion, but this seems to me like a sidereal tracking problem.

Does PHD2 have a tool or method for determining the accuracy of the mounts sidereal tracking?

Thanks for your help,

Mark

[Bruce Waddington]

It won't be a problem with the sidereal tracking rate, the RA drift will almost certainly be coming from a different source.  You should do an extended run with the Guiding Assistant (>= 1 worm period) then analyze the guide log to see how the native RA tracking behaves.  You can do that yourself using the PHD2 LogViewer or you can upload both the guide and debug logs to our site and we can help you analyze it.

https://openphdguiding.org/phd2-log-viewer/

https://openphdguiding.org/getting-help/

If you want us to look at the data, we will need to know more about your setup, in particular whether you are using an OAG or a separate guide scope.  On a long focal length setup like yours, using a guide scope will be a challenge and doing so is the most common source of large RA drift.  But only the data will tell for sure.

Regards,

Bruce

[Brian Valente]

Adding to Bruce's good suggestions, the RA tracking sidereal rate is almost never the problem. 

Producing an unguided output (i.e., 'extended run with the guiding assistant') will certainly help clarify what's going on.  

Another resource to consider is this pdf from Astro-Physics that discusses other possible causes of RA drift

https://astro-physics.info/tech_support/mounts/potential-causes-ra-drift.pdf

Brian

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Brian 

Brian Valente

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

[niteman1946]

Thanks Bruce and Bryan for the responses.

I'll dig into your recommendations.

Mark