Starlight Xpress Active Optics Bump questions

[The Galaxy Hunter]

Hello everyone,

I am trying to figure out the right settings for my new Starlight Xpress Active Optics system. What I am experiencing is that it guides well for about 2 minutes, then, for some reason, the guide star begins to drift (ra) and never recovers.

For context, my balance is quite good. My polar alignment is off by 0.1 arcmin and my pointing is nearly perfect. My guidestar on the OAG is also well focused. I've tried to eliminate all of the obvious normal defects that impact guiding and i feel that I have eliminated all of them.

My FL is 2000 and currently not using any flatteners or filters. I found that I had best results setting the exposure interval to 0.5 seconds.

My question has to do with page 30 of the documentation:

  "You will want to initiate mount 'bump' corrections before these limits are actually reached, and the 'bump percentage' field is used for that purpose. If the bump operation has begun and the guidestar remains outside the "bump percentage "area, PHD2 will increase the bump size until the guidestar is back within that range "

My guess is that my problem has to do with PHD not bumping enough (or not bumping at all). I'm a little confused about what the documentation is telling me to do. If I reduce the bump percentage, should I expect a bigger bump or a smaller one? Is the Bump Steps setting more effective for increasing the bump? My interpretation is that I should reduce the AO percentage and increase the bump steps. Please correct me if my interpretation is wrong.

I have found that reducing the AO travel field was effective for reducing the peaks and valleys in my guide graph. It seems to guide well for about 2 minutes, then the guide star starts to drift and never recovers. 

I am hoping that someone with more AO experience can help me understand these settings.

Thanks much,

Jaime   

[Brian Valente]

Hi Jaime

you need to provide logs for us to review

https://openphdguiding.org/getting-help/

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Brian 

Brian Valente

portfolio brianvalentephotography.com 

[The Galaxy Hunter]

Hi, thank you for responding so quickly. The log file can be found at https://openphdguiding.org/logs/d1/PHD2_logs_PWLk.zip. I will caveat by saying this uploaded night was my first night of testing and my balance was not perfect and my polar align was off by 18 arc-min. The guidestar drift after about 2 mins was the same. Thank you Brian!

[The Galaxy Hunter]

Just a quick followup question. In the PHD2 connections dialogue, should I connect to three devices or two? Currently, I am connecting to the guide camera and the SX AO unit (2 connections). I'm wondering if I should connect to guide camera + Celestron Mount + SX AO unit (3 total connections)? Thanks much.

[Bruce Waddington]

In order to “bump” the mount, you need to have a ‘mount’ connection – the ASCOM mount driver would be a good choice.  Without a mount connection, you will only be able to guide as long as the guide star deflections stay within the physical limits of the AO’s tilt/tip machinery.  When you use a ‘mount’ connection, PHD2 will calibrate both the AO device and the mount – so you’ll initially see two calibrations.  You also need to be sure that guiding works reasonably well through the mount connection and settings like ‘reverse Dec after meridian flip’ are set correctly. 

 

Hope this helps,

Bruce

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/cf508864-d780-4423-a5a4-5ce55b0860fbn%40googlegroups.com.

[The Galaxy Hunter]

Thanks for getting back Bruce. I was able to figure that out and test it shortly after my last email. I used the On-AO selection under the mount dropdown and that was all I needed to do. Now the AO works (and works well). My RMS error dropped to between .3 and .5 px compared to 1.25 to 2.0 previously using a piggyback scope. Remarkable improvement.

To your point, the PHD graph did exactly what you said. The tracking was perfect for as long as the mount stayed within the parameters of the AO. Then the smooth lines just drifted off the graph.

Just to close the loop on my initial post, the settings that I found to work best in PHD2 are the following:

AO Travel=20

Bump %=50

Cal Steps=1

Bump Steps=3

Backlash pulse=turned off

hysteresis algo @50 aggr

FL=slightly higher than known value

Dec balance=perfect

RA balance=slightly counterweight heavy

Polar alignment~.1 arc min

Again, I am imaging @ 2032 FL using a CGE mount for reference.

A general comment I have is that the PHD documentation was helpful with AO, but I would encourage the document to specify the On-AO choice or a second com port connection to the mount. I have never used the st-4 port connection on my guide camera, so it didn't occur to me to look for the On-AO connection. One or two more sentences in the document could really tighten up those instructions in my opinion.

Thanks for all of your help.

Jaime 

[Bruce Waddington]

We’ll try to improve the documentation in this area, it’s pretty vague.  But “on-AO” is not the recommended mount connection, that’s why I was encouraging you to use the ASCOM mount driver for your Celestron.  It’s best to avoid ST-4 guiding in any form when possible including AO bump operations.

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/f4c15408-0650-48e4-8ab8-b9dcd44912f8n%40googlegroups.com.

[The Galaxy Hunter]

Got it. That's good to know. I will take your advice and try a direct connection with the mount next time I am under starlight. Thanks for the followup. This really helps.