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

Roland Christen

That is why I recommend using a short unguided Dec graph to determine the actual atmospheric motion peak value. Then set the MinMove to between 60 and 80% of that value. If the star motion is +-2 arc seconds peak to peak, then set the Min Move to 1.6 arc sec (or 0.48 pixels for a 3 arc sec per pixel scale). I don't know how much more clear I can make this.

If you set the MinMove to less than this value, you can guarantee you will have oscillations caused by guider chasing the seeing. Remember, you are trying to re-position a mechanical gear wheel by a few nanometers even at 1.6 arc seconds.

All we're trying to do in guiding Dec is to set a boundary within which we allow the star to bobble back and forth unimpeded. If it exceeds the boundary we want to nudge it gently back towards zero. We do NOT want to set up small rapid oscillations back and forth which can get out of hand.


-----Original Message-----
From: stephenjwinston@... [ap-gto]
To: ap-gto
Sent: Tue, Jul 10, 2018 10:25 am
Subject: Re: [ap-gto] Re: Things that customers do that drive me nuts on CN

>You say that you have seen peak Dec errors of 3.71 arc seconds. Well the fact is that this error happened in the past and the next measurement may show a different position of the star,

Again, to try clarify:  The 3.71 arc seconds error is what PHD2 Guiding Assistant measured as the Peak Error while calibrating with DEC tracking disabled.

Bill had suggested that users should us the Peak Error from PHD GA to set MinMo.

I was just making the point that the GA measured Peak Error is not necessarily the right metric to set MinMo - in my case it would mean setting MinMo to 1.25 px

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