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Tracking issues after meridian flip

William Optics Redcat 51 Sky-Watcher EQM-35 Pro Acquisition Meridian Flip Deep Sky
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Chase Davidson avatar
Chase Davidson avatar
Hi everyone,

Been a little over a year into my astrophotography hobby and I've dove head first. Upgraded my mount from the EQM-35 pro to the AM5 a few months ago and I love the ease of use. I also upgraded my scope to the Astro-Tech 130EDT from my original RedCat 51. The 910mm scope (reduced to 730mm with the 80% reducer) is pushing the limit of the AM5 but I have gotten a lot of good images from it.

One thing that I have consistently noticed is around and directly after the meridian flip I have HUGE star trails. I don't have an extension for the mount yet so I have been keeping a close eye that the camera is not hitting the legs of the mount but I still have extreamly bad tracking around the meridian. I ensure to auto-focus after the meridian and every 1 hour afterwards due to my area's humidity but I still cant get the tracking to get back to normal. The auto-guider doesnt seem to be having large variances during this time on the ASI Air app, it just seems the mount is not keeping up with the tracked star after the meridian. Anyone else experience this?

I have included a pic of my subframe selector measures of Eccentricity and Star Count to better visualize this issue. The meridian occurs right at ID 45, where the majority of the bad data starts to happen.

Thanks!
Chase
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Taylor Ryle avatar
Taylor Ryle avatar
Do you recalibrate guiding after the flip. There is an option for it in the asiair settings I think under the mount tab/meridian flip. I normally don't have this set on but it might be something to check out.
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GiffS avatar
GiffS avatar
My experience has been that without re-calibrating after the flip guiding will never properly recover.  That’s a drag because it eats almost 20 minutes of imaging time and at least 2 subs will have streaking stars but then everything settles down and guiding resumes normally.
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NeilM avatar
NeilM avatar
have you checked that you are more or less balanced on both sides of the meridian?  There is a controversial topic called "3-D balancing" (look it up if you want to go down a rathole!) - but the bottom line is that being balanced in one position doesn't necessarily translate to all positions.  If the balance is badly off after the meridian flip, this off this would contribute to poor tracking.
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Chase Davidson avatar
Chase Davidson avatar
have you checked that you are more or less balanced on both sides of the meridian?  There is a controversial topic called "3-D balancing" (look it up if you want to go down a rathole!) - but the bottom line is that being balanced in one position doesn't necessarily translate to all positions.  If the balance is badly off after the meridian flip, this off this would contribute to poor tracking.

Got to take my rig out for the first time in a few weeks tonight and noticed the western tripod leg was shorter than the rest. Gotten into a bad habit of not checking everything and just bringing it out and turning on Asiair. If this is the issue I’m not sure the meridian flip was the issue because I have it recalc-ing the guide after the flip. It’s probably just the closer the scope comes to the west, the more off the polar alignment gets?

I balanced it tonight so hopefully I’ll see an improvement on tracking later in the night. I’ll update everyone tomorrow.
Brian Puhl avatar
Brian Puhl avatar
I think you might have some greater underlying issues here.     Your eccentricity values are extremely high even before the flip.      How does your guiding perform overall?
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Chase Davidson avatar
Chase Davidson avatar
Brian Puhl:
I think you might have some greater underlying issues here.     Your eccentricity values are extremely high even before the flip.      How does your guiding perform overall?

Yeah good question. Since I’ve started using the AT130 and the orion 50mm guide scope I’ve gotten consistently under 1” on guiding but it jumps around a lot. I can’t tell if this is normal, especially for a larger scope. I usually end up throwing out 60%-70% of my subs because of bad eccentricity or star trails. Here’s example of tonight’s tracking and my settings.
Brian Puhl avatar
Brian Puhl avatar
Chase Davidson:
Brian Puhl:
I think you might have some greater underlying issues here.     Your eccentricity values are extremely high even before the flip.      How does your guiding perform overall?

Yeah good question. Since I’ve started using the AT130 and the orion 50mm guide scope I’ve gotten consistently under 1” on guiding but it jumps around a lot. I can’t tell if this is normal, especially for a larger scope. I usually end up throwing out 60%-70% of my subs because of bad eccentricity or star trails. Here’s example of tonight’s tracking and my settings.



those are some pretty substantial spikes there!   Almost 3 arc seconds.    Your image scale is roughly 1 arc second.  The rule of thumb I've adopted is guide performance should be better than 70% of image scale, and any spikes outside your image scale should raise concern.   Your RMS might suggest it's good, but those spikes are whats killing eccentricity.

I don't know alot about these harmonic mounts, but I would suggest you spend some time balancing that scope out.  Your issue, as far as I can tell has nothing to do with meridian flip.  If you don't have a counterweight installed, start there.   Beyond that, I'm hoping an AM5 owner can chime in, but I suspect you're asking ALOT out of that mount slinging a 130mm scope.
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