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Issues with guiding (or tracking?) [Deep Sky] Acquisition techniques · akshay87kumar · ... · 7 · 272 · 3

akshay87kumar 3.01
akshay87kumar
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I am having weird issues with guiding - getting very high guiding errors. My guiding, when I start the plan, begins as bad as 8" in both RA and DEC, takes a long time to remain in 3"-4" region, and finally stabilizes around 2"-3". Could you please help me diagnose what could be the issue?

Guiding/Tracking Equipment: ZWO ASI120MM, WO 50mm guidescope, iOptron CEM40, ASIAIR
Telescope: WO 71GT APO, ASI294MC Pro, 120s exposures.
Settings being used: Standard ASIAIR settings without much changes.
  • Medium Gain, 1" exposures for guiding
  • Calibration step: 2000ms, Max DEC Duration: 2000ms, Max RA Duration: 2000ms
  • Dither by 2 px after every 3 frames. This is turning out to be a big problem that throws the accuracy to as poor as 20"-30" for about half a 20-30 seconds. I understand the mount moved, so it will become poor, but this seems really bad.

I did check the polar alignment too a couple of times - I polar align to accuracy within 1' (as per ASIAIR). I have been seeing people getting accuracy < 1", which seems like a very far fetched thing for me at this time (and is very disheartening too).

I am not using a field flattener at the moment, so please focus on the center stars. Posting screenshots of dithering and the image.

Screenshot_20241106-233109.jpg

Screenshot_20241106-233433.jpg

Light_M 42_120.0s_Bin1_294MC_Lext_gain120_20241106-231338_2.1C_0006.jpg

Can you please help diagonose what could be going wrong, or any settings I am not having correct? Appreciate all your inputs and help.
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afd33 9.38
Quinn Groessl
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A few things I would try: Up the gain on your guide camera a bit. I would also try 2 second exposures. And check your focus on your guide scope. After that I would play around with the RA and Dec aggression a bit. I've always upped mine until it started to kind of flip flop on the direction of the correction, meaning it's over correcting a bit. Then I back it down a bit so that it's mainly correcting the same direction all the time.
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Joo_Astro 3.80
Johannes Maximilian Möslein
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First, you probably need to polar align better. Below 1' should definitely be possible.

Some standard questions:

Is your equipment balanced in both axes?
Everything tightened down? 
Enough power to all devices?

What's the guiding speed in the settings, 0.1, 0.5, 0.9?
I don't have the 120MM, but 28 gain seems way too low. Also, at 350mm focal length you should do longer exposures than 1" for guiding. These 2 things combined should improve things.
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Stephen.J 1.43
Stephen Jones
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Suggest that you read this as it has the formula for your calibration steps for starters.  The bottom link will help you with sidereal rate etc.
https://www.astrobin.com/forum/c/equipment-forums/zwo-asiair-plus/asiair-calibration-settings-for-using-and-oag/

https://eastwindastro.blogspot.com/2021/02/how-to-adjust-asiair-guide-aggression.html
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akshay87kumar 3.01
akshay87kumar
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Thanks everyone. I will go through the documentation shared and get back with any clarifications. Appreciate all your help!
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patrice_so 7.87
patrice_so
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Just a note : you may want to dither more than 2 px for your dithering to be effective. Try 10.
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akshay87kumar 3.01
akshay87kumar
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Quick update - I thoroughly reviewed the settings in ASIAIR and realized a blunder. I use a WO 50mm f/4 guidescope, and I had put the guide scope focal length as 50mm (instead of 200mm)! Instant fix, now I am getting guide errors of ~0.4-0.9" in either axis, adding to overall RMS of less than 1.5". Still a bit to improve, but glad to realize that my equipment is not incorrect, neither is the effort in coming so far unfruitful! However, will plan to go through detailed documentation to understand the nuances of guiding.
And the stars are definitely much more sharper now!
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ScottF 4.52
ScottF
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It's good to see you found a solution. One thing I would add is that it is important where in the sky you calibrate the guiding. I usually calibrate a little east of the meridian and celestial equator intersection, and it works well for me.
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