I have had no end of frustration trying to get nice round stars. They always seem egg shaped.
Worse, the direction of elongation is not consistent.
My mount is an EQ-6 Pro.
On my OTA, the C11, I have re-aligned the primary, secondary and corrector plate as per Celestron specs.
I even tried using my WO80 instead of the C11 and still get eggs for stars.
Its not in a particular part of the image, it is usually every where but not always.
Now, I have done polar alignment many times, I did 3-star alignment many times and still EGGS
Now, the other night, I though I would do a PE check using PHD and PEAS. I got wonderful data but, I forgot to disable the guiding output.
Here is the PEAS output.