Odd guiding behavior

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RidesForever
Posts: 11
Joined: Wed Sep 27, 2017 6:26 pm

Wed Nov 08, 2017 4:28 am

After the most recent update to v10.3.34.36, I get odd behavior in guiding – here's a screenshot of what I'm seeing
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Capture.PNG (42.66 KiB) Viewed 2724 times
“I” can see the guide star, but Prism thinks it’s somewhere else.
I’m using an ST-I guide camera off-axis on a QSIwsg8 camera. Scope is an AstroTech 10” RC
Not sure what I’m doing wrong, but figured there are some settings that could be tightened up to minimize this?
I tried selecting the full frame option, but that was bad (really bad!). It kept skipping to different stars and moving the mount all over the place
I also tried increasing the minimum star ADU a little bit thinking it would look at the brighter blobs on the frame, that didn’t seem to make any difference
I have noticed this happens more frequently on nights with poor seeing, but the odd thing is that light clouds doesn’t seem to affect it much.
I did tighten up the focus on the guide camera and re-collimated the scope – that helped a little, but I’m still seeing this happen more than I think I should
Any hints for dealing with this?
Hamza Touhami
Site Admin
Posts: 564
Joined: Sat May 20, 2017 6:05 pm
Location: Phoenix,AZ
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Wed Nov 08, 2017 9:05 pm

Hi
You guide star looks adequate and it is lot better than my off axis ones :lol: . Some suggestions:

- Try a 50 x50 subframe, I think 152 x 152 is too big is more prone for having other objects in there like stars, hot pixels, etc..
- When you press the "Start" button from you guider's guiding tab, check the option to pass a 3x3 median filter ( example attahced ). This will help with hot pixels greatly.

I would try these options one at a time and see what the result is, please report back when can.

Thanks
Hamza Touhami | Site Administrator
Hyperion-Astronomy.com
RidesForever
Posts: 11
Joined: Wed Sep 27, 2017 6:26 pm

Thu Nov 09, 2017 6:04 am

That is an off-axis guide star! (QSIwsg8 on an AstroTech 10"RC)
It did take a while circling the object to find a nice bright star :)

I think I changed the window size when I first started having problems. I'll shrink the window back to where it should be, add the median filter and let you know what happens!

Thanks
Margo
RidesForever
Posts: 11
Joined: Wed Sep 27, 2017 6:26 pm

Tue Nov 21, 2017 5:45 am

Sorry for the slow follow-up...
I employed your suggestions and have worked with guiding the last few clear nights.
Here's some followup:
I shrunk the guide star window back down to 50x50. Big improvement
I added the median filter - another improvement
These two changes got the guiding behavior back to normal!
At this point, I was getting an average guiding error just below 2 pixels. With an OAG at a focal length of 2000mm, I think that's reasonable.
I also tweaked the collimation and focus of the guide camera. This improved it a tiny bit more, so I'm down to 1.7-1.8 average pixel error for the night

Thanks for your help!!
Hamza Touhami
Site Admin
Posts: 564
Joined: Sat May 20, 2017 6:05 pm
Location: Phoenix,AZ
Contact:

Tue Nov 21, 2017 5:32 pm

Thanks for the report, I am glad things are back to normal.
Hamza Touhami | Site Administrator
Hyperion-Astronomy.com
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