Re: Mach2 - Elongated stars


Roland Christen
 

If your guiding was spot on, then the mount is working correctly. It is not a balance or setup issue. Balance would not cause oval stars. The mount would be suspect if one axis had rms guide values that were twice as high as the other axis.
Dec correction mainly in one direction means your polar alignment in azimuth was off. You can see that if you turn correction off and let the mount drift in Dec.
Elongated stars top to bottom ? you did not specify if that was RA or Dec.

Rolando

-----Original Message-----
From: yanzhe liu <liuyanzhe@...>
To: main@ap-gto.groups.io
Sent: Sun, Mar 7, 2021 12:44 am
Subject: [ap-gto] Mach2 - Elongated stars

Testing new mach2 for a couple of nights. It works great out of the box and I am very pleased.

One issue bothering me is that I got slightly elongated stars across the entire image (15min Ha sub).
The exact same telescope/CCD were used with another mount and stars were round, I am wondering what I should check (I think there was due to some setup issue, but I could not figure it out).
- Used OAG for guiding, so there should not be any flexure.
- CCD orientation was 0/180 degree. The stars were elongated top to bottom.
-  I did polar alignment with PHD2 drift align. PA error should be < 5'. The field rotation of each sub is ~0.01 degree, much larger than the other system (but elongated stars do not look like field rotation, they were same across the image)
- Both RA and DEC guiding curves looked smooth, had similar RMS. DEC correction was mainly to one direction.
- DEC balance was slightly off, camera heavy. Is Mach2 DEC sensitive to this? Will the guiding/image be affected?

I dont think any of the above is of particular concern, except DEC balance. Any comment/help is appreciated.

--
Roland Christen
Astro-Physics

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