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Change in guiding after the meridian flip

Stark Labs PHD Guiding Meridian Flip M81 NGC3031 Messier Objects
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Tony Barlow avatar
Tony Barlow avatar
Can you guess where the meridian flip occurred? Any idea what might cause this? Target was M81, iOptron GEM 45, Takahashi Epsilon 180 ED, ZWO 2600mm. The scope is balanced, I tried making the RA slightly out of balance but it made no difference.
Thanks,
Tony
Richard Carande avatar
Richard Carande avatar
What kind of guiding equipment are you using?  Certainly an OAG will be using a completely different star field to guide with – perhaps the stars are brighter or somehow better after the MF in your case.  Maybe the auto-focus was not working well before the MF.   I think even using a guide scope, you may be seeing different star fields.  Just a guess…
Tony Barlow avatar
Tony Barlow avatar
Hi Richard,
Thanks for the comment.
I'm using a 70mm guide scope and it is very closely aligned with the main scope. I talked with Adam Block and the main thing I came away with is setting the Periodic Error Correction, PEC, on the mount. I'll be doing that tonight. If it make a big difference, I'll post a new image of the guiding.

Regards,
Tony
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Oscar Echeverri avatar
Oscar Echeverri avatar
I have a similar problem with my iOptron CEM70 where guiding before the meridian can be unstable.

Mine seems to get into an oscillation in DEC that nearly doubles the guiding error compared to guiding on the other side of the meridian. What do your guiding graphs from PHD look like?

I've mitigated my oscillation issue by only guiding in DEC in one direction (against direction of my polar alignment drift)  and I get numbers nearly as good as when I guide in both directions on the other side of the meridian.
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Willem Jan Drijfhout avatar
Willem Jan Drijfhout avatar
Tony, have you been able to track down eventually the alignment issue of your IC1805 image? Could it be field rotation, due to poor polar alignment? M81 has very high altitude at the moment, and if PA is off by a few arcmin, that can become pretty visible. Perhaps to the point that the guiding, calibrated at much lower altitudes, can't keep up with it anymore. Like mentioned before, the PHD2 logs might  give you some answers here.
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Habib Sekha avatar
Habib Sekha avatar
Could there be some play in the focusser?

I know a few Epsilon users where the collimation is perfect on one side of the meridian but less good on the other side.
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Tony Gondola avatar
Tony Gondola avatar
It could also be a mechanical issue with the focuser slipping just a bit while the scope is going through it's motions. a slight tug from a cable could be the cause also. does the guiding accuracy return to normal after awhile or does it remain degraded?
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