Re: Fine tuning PHD2 settings for 1100 with Encoders #Guiding

Roland Christen

I still don't see a screen shot of the RA and Dec unguided tracking graph, so I really cannot explain to you how the results of that graph will show you what is happening. It is the key to setting the Min Move for any given night, which is really the most important setting. You want to set MinMove such that the guider loop does not chase random sky motion due to seeing. The numbers below give a clue but they cannot get you to understand the why. That is what I wanted to be able to convey to you and others who may be watching this newsgroup.

Please post a short 2 - 3 minute guide graph taken with 1 second guide exposures and corrections turned off. The easiest way to turn corrections off is to set MinMove to 20.0 for both axes. No need to do a GA or other fancy tests.

Why is it that people don't want to do this simple test? It's not hard and takes literally just minutes, but reveals everything you need to know. And i will explain it all in an annotated visual once I get your graph.


-----Original Message-----
From: Andrew J <andjones132@...>
Sent: Mon, Oct 11, 2021 2:11 pm
Subject: Re: [ap-gto] Fine tuning PHD2 settings for 1100 with Encoders #Guiding

Hi Brian.

This is really helpful!! You are right, as a software developer I keep thinking this is just an equation that needs to be solved and all I need is the right inputs. No doubt there is some "artistry" involved. That said, I do want to at least understand what the 'theoretical" settings should be and use those as my starting point.

I think in large part I am just getting hung up on the terminology. If I look at this output from PHD2 Guiding Assistant, are you saying that my P-P Arc Seconds is the Declination, Peak of 0.73 px (1.44 arc sec)? If yes, how does this help me determine what MinMo I should use as a starting point? I took this screen shot before I hit the finish button, but it came back and recomended a RA MinMo = 0.20 and a DEC MinMo = 0.30. 

As mentioned in a previous post, I did another imaging run on Saturday night and all I changed was the aggression on both axis to 0.63 or RA and 0.72 for DEC and my graph fattened out quite a bit. I was able to achive an RMS of 0.23 on one point during the night. I think by relaxing the Aggression it alllowed the encoders to "do their work".

I have been imaging from a permant setup for about 6 years now (previously with a Mach1) and guiding has always been my achillies heel. I get it close enough to get round stars, but have to admit I really don't understand it. Now that I have a mount that can track extreamly accurately, I want to make sure I am using it to its full potential. 

FYI. In case it helps. In addition to the 1100GTO mount, I am also using a  Tele-Vue NP101is. I bought this scope specifically for the 1100's "shack down cruise". I wanted a short scope to give me plenty of room for error around the Pier until I get APCC, SGP, etc. fine tuned. My primay scope is a TEC 140, but I am not putting on until I get everything working together and able I am able to have several all night imaging runs without issue. For guiding, I am use the Baader Vario Finder 10x60 along with AP's bracket to help reduce flexure. Primary camera is an ATIK 16200 and guide cam is a ZWO ASI178MM.


Roland Christen

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