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PHD2 DEC Backlash issue on CGX

astrophotography Celestron SCT
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#1 skaiser

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Posted 20 March 2019 - 02:31 PM

I have  Celestron CGX mount with a 9.25" SCT scope mounted on it.

I am using a Celestron Off Axis Guider with a ZWO ASI224 camera.

I am trying to use the PHD2 calibration assistant to setup parameters for backlash in my system.

Every time I run the Backlash mode , the guide assistant says my DEC backlash amount is way out of range ( something like 3200?) and cannot compensate properly.

I know I have some minor amount of backlash but I don't think it is that extreme.

I have checked to make sure the Dec drive gearbelt pullies are tight on the shafts.

No belt slipping or binding.

 

If I ignore PHD2 warnings and run  guided, the graph is showing guiding typically 

RMS error (px)

 RA 1.8     DEC 0.7

 

Anyone else using PHD2 guiding for a CGX mount see this problem?

Thanks



#2 rgsalinger

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Posted 20 March 2019 - 04:10 PM

First, if the stars are round in your exposures, then nothing else matters. If you are imaging at F10 with that scope then the RA RMS pixels translates into around .6 or so arc seconds and the DEC is .3 arc seconds which is amazing for that mount/scope combination. That is truly excellent guiding. So, it is much more likely that something is wrong with the guiding assistant and/or your PHD parameters than anything else. Even at F7 the numbers will look good enough to get excellent results.

 

Rgrds-Ross




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