Re: RA Mesh adjustment for 2104 model Mach 1 GTO


Hi Nicholas

I'm a little confused/concerned about these large and fairly instant jumps in DEC

I see it happened a couple of times. I don't see it affecting RA, so it looks to me like something is loose in your imaging train for this guiding setup?


On Thu, Oct 14, 2021 at 9:47 AM Roland Christen via <> wrote:
Hello Nicholas,

The good news is that your mount is working fine. Both the RA periodic error curve and the Dec backlash curve are well within reason for this old mount. I don't see any sign of stiction in Dec, so it will guide quite well in that axis. RA is between 8 and 10 arc seconds, which is slightly out but not enough to cause any guiding problems. So, the mount is healthy and will be able to do imaging with a 6" refractor just fine. Your 6" is not too large for the Mach1. The mount can actually handle somewhat bigger scopes and guide well.

I do have some comments about your settings:

First, your high frequency star motion (seeing) is very high, you must be either experiencing some air flows from an east wind over the mountains, or your particular location is just not very steady for seeing (2.66 arc sec star motion as reported in your GA is very high). If it really is that high then your setting of Min Move (0.18 for RA and 0.23 for Dec)  is totally wrong and it shows in your RA Guider graph when you started guiding. Such a low setting of Min Move will cause oscillation back and forth as the guide software tries to chase the seeing. Your GA run recommended 0.39 for RA and 0.6 for Dec. I would start with those settings, but if the guide graph doesn't settle down I would increase RA to 0.5 or 0.6, same as Dec. There is no reason to try keeping the RA axis to such a low threshold as 0.18 arc seconds. When I am guiding even with my largest and longest scopes I rarely ever set the min Move below 0.3 arc seconds.

The other thing I would do is to set the aggressiveness for both axes to 50% when the seeing is not good, and only increase it to 70% under very good seeing conditions. Seeing is NOT transparency! Seeing is high frequency star motion or the back and forth motion that you record in the Dec axis when no guide pulses are being sent.

It is imperative that you Do Not set any backlash compensation in your guide software, and that you always use 1x guide rate. Normally I would guide with 2 to 3 second guide exposures. That will help to smooth out the star motion and minimize chasing the seeing.

You can guide with the present RA periodic error of 8 to 10 arc seconds since that occurs over a 6.4 minute cycle and is slow enough for your guide software to handle. However, if you ever want to really get your mount tracking well, then you might consider using PEMPro to create a PE curve and feed it to your CP controller. Then turn it on and watch the mount's RA tracking improve dramatically. However, it will only work if you do it right. If you mess up the measurement and don't follow the instructions, you can easily make things worse. It's up to you if you are confident that you can do it right. Even if you mess up, you can always turn the PE correction off.

Finally, Some of your previous runs show a very high Dec drift rate which is an indication that your Polar Alignment is quite a ways off. A Dec drift rate of 1 to 2 arc seconds in a 5 minute period would be ideal, in your case it was more than 10 times that amount, and this will limit your ability to get tight guiding and tight sharp stars. You will get all kinds of recommendations but just pick the one that works for you and stick with it. Polar alignment the same way each time will give you consistent results.

Good luck and fair skies.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: nicholas via <>
Sent: Thu, Oct 14, 2021 2:49 am
Subject: Re: [ap-gto] RA Mesh adjustment for 2104 model Mach 1 GTO

I posted the GA ss above if that is what you mean.

there is this which Andrew generated of the test run n
I have not gotten to PEC yet. 

the attached Phd2 ss is from current guide about 25 minutes thereof.

Roland Christen


Brian Valente

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