Mach2 - Elongated stars

yanzhe liu

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.

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