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Guide Star Shift with ASI 2600 MC Air

ZWO ASI2600MC Pro Equipment Guiding Troubleshooting
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John Noble avatar
John Noble avatar
I recently bought myself the 2600 MC Air and overall I’m delighted with it. I’ve been using both off axis guiders and guide scopes for years and have got used to the constant tinkering to prevent differential shift of the guide star.

Perhaps foolishly I had thought that would be a thing of the past with the air but alas not! It’s not a massive issue (last two nights I lost 6 frames out of 96) but I’m keen to hear what others have found.

Bottom line I’m assuming this is because something is moving the camera body relative to the light beam (a tiny rotation) - I’m guessing cable pull or gravity or both. 

just wanted to check I’m not missing something. There isn’t anything loose or any obvious cable issues.

Im shooting at 910 mm focal length.

Thanks

John
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David Russell avatar
David Russell avatar
John, I am not an expert but I thought the idea behind the duo was that flexure is eliminated.

those lost subs might just be camera movement from other causes. bumps, wind, worm gears etc….

whats you guiding doing in RMS ?
Alex Nicholas avatar
Alex Nicholas avatar
Don't think you're getting flexure. Something else is at play.

Guide RMS won't help, because RMS is exactly that. The root mean square of all guide corrections. 1 or 2 big jumps won't affect your overall guide rms, but it will ruin a sub exposure… 

I'd be watching your guiding as it happens. Spend a night watching the whole rig, watch every subframe come in and when you see a dodgy one, look at the guide graph.
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Tony Gondola avatar
Tony Gondola avatar
It's not flexure as others have mentioned. It's not unusual to have a bad frame now and then. It can happen even when your guiding is sub 0.4" RMS. It could be seeing, the mount, wind gust, a cable pull or god knows what else. As Alex said, look at your guide graphs. The best performance comes with a smooth graph, a balanced RA DEC error and a low RMS. This is the world we live in until cameras and hardware gets good enough that you can shoot with 0.1" subs. At that point, you won't need to guide and all these expensive mounts will go away. Until then, guiding is a necessary evil.
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John Noble avatar
John Noble avatar
Thanks all I’m pretty sure this was cable pull. I did a bit of tidy up and was able to get 48 good frames in a row so I will call that a success!

thanks again

john
Tony Gondola avatar
Tony Gondola avatar
Glad you worked it out!