discrepancy between 3PPA N.I.N.A and guiding assistance PHD2

[Krzysztof]

please let me know what can cause the difference in PA error between 3PPA PHD2 and Guiding  assistant  as in the below pictures

what can I do wrong?

Mount CEM70 ,Ioptron Commander 8.

thanks for any inputs, Krzy

[wave...@talktalk.net]

Hello Krzy,

I'd say you're not giving PHD2 Guding Assistant sufficient time to determine an accurate result.

I doubt the PA error calculation after only 49 seconds of operation means anything.

You should leave the GA running for several worm cycles to allow the effects of periodic error to be properly measured.

To get an accurate result, I leave the GA running for 15-20 minutes or more, over which time the displayed PA error initially reduces rapidly and then begins to settle to the final value.

Cheers,

- Jack

[Krzysztof]

Hello Jack,

It was only an example. I did 3 minuts run and no better result.but will try much longer time. It happened first time. Previously, it came very fast to proper value - nearly the same as 3PPA.

Thanks and regards,krzy

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[Bruce Waddington]

The Guiding Assistant is estimating polar alignment error based on the rate of Dec drift when no guiding is active.  To get an estimated error this large, you had a lot of Dec drift. Sources of these kind of measurement differences include:

 

1.       Mistakes in using another app’s alignment tool.  Polar alignment always requires mechanical adjustment of the mount to align the right ascension axis with the celestial pole.  Software-only “alignment” methods sometimes just compute a quick pointing model that will improve slewing accuracy without achieving real polar alignment of the axis.

2.      Not tightening the mount’s azimuth/altitude adjustment bolts sufficiently, thus allowing the mount to move around when slewing

3.      Gross imbalance of the scope in Dec

4.      Loose fittings on a guide scope assembly that allow the camera to sag or move around because of gravitational load

5.      Using an old PHD2 calibration that no longer reflects the correct rotational position of the guide camera. This is probably the easiest thing to rule out – if the GA reports a huge error like this, try re-calibrating and re-running the GA.

 

If you confirm the PHD2 calibration is accurate and still get these large alignment error measurers, you will have to find whatever is causing the apparent drift in Dec.

 

Good luck,

Bruce

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