Re: Things that customers do that drive me nuts on CN

W Hilmo

Let the mount run unguided for a few minutes while watching the graph.  Throw out any really big outlier values and take the peak from what is left.  Taking the RMS seems like it would guarantee that the mount is going to chase seeing.


Seriously, if the mount is well polar aligned, the only thing that you want to correct for in declination is a fairly small amount of drift.  The drift should be slow, consistent, and always in the same direction.  If the declination guider is constantly issuing corrections, or (especially) changing directions frequently, then you are chasing seeing.  You really want to be having infrequent corrections.




From: ap-gto@... [mailto:ap-gto@...]
Sent: Tuesday, July 10, 2018 7:45 AM
To: ap-gto@...
Subject: Re: [ap-gto] Re: Things that customers do that drive me nuts on CN



Hi Bill,


I wanted to come back to the "right" way to use GA to determine the MinMo values, as I agree it is critical that these be set correctly.


Specifically for setting DEC MinMo you wrote:


>Look at Peak DEC error. It gives it to you in both pixels (which you need for PHD MinMo) and Arc-Seconds (which you need to talk to people with).

>Set MinMo to Peak DEC error value GA gave you

I'm not sure if you really meant "peak" here.  I've uploaded a screen grab of my calibration run last night.  During GA the measured peak DEC error was 1.25px or 3.71 arc-s.  As the peak error can be affected by any number of sporadic things (sudden spike in seeing, glitch in mount tracking etc), I don't think it provides the right baseline to set DEC MinMo.  

The RMS number gives a better measure.   I have seen suggestions to set MinMo to 2x the RMS  which was 0.12 px / 0.36 arc-s for me, so that would have put my DEC MinMo at 0.24 px.  Perhaps the right multiplier needs to be bigger at 3x or even 4x the RMS.

As I mentioned in an earlier post, Bruce already agreed that the current MinMo recommendations can be too optimistic/aggressive.  Having PHD2 come up with more realistic recommendations will help (especially beginners) get off to a good start.





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