ttrostel Do you know if the polar alignment routine in the ASIAir pro corrects for atmospheric diffraction?
I assume you mean atmospheric refraction? Atmospheric diffraction would contribute very little to the centroid of a star on top of refraction, which is moderately large at low latitudes, and needs to be corrected.
If so, then I am pretty sure atmospheric refraction is included in ASIAIR.
I just tested ASIAIR with my Mount Simulator, which projects a image of the sky on a display, then to a camera that is connected to ASIAIR.
http://www.w7ay.net/site/Applications/MountSim/
My simulator can include no refraction, or refraction that is given by Samundsson. (See above documentation about 3/4 of the way down the page.)
When I ran the ASIAIR Polar alignment on my simulator and ASIAIR set at a latitude of 10 degrees North, I get a residual error of about 20 arc seconds from the pole, with atmospheric refraction turned on. The majority of the 20" error is probably from a misalignment of the optical axis of the camera; I only roughly collimated the optical axis for a quick and dirty measurement.
When I turned my simulator's atmospheric refraction off, I see a residual error from ASIAIR Polar Alignment of 5 arc minutes in the altitude direction and 2 arc seconds in the azimuth direction. If you check this graph from Wiki, atmospheric refraction at 10 degree latitude is just about smack at 5 arc minutes:
https://en.wikipedia.org/wiki/Atmospheric_refraction#/media/File:BennettAtmRefractVsAlt.png
Notice that I am applying a forward (Samundsson's approximation) atmospheric refraction in my simulator, while ASIAIR is applying the inverse. Both are approximations of real life. In the second case above, I applied no refraction, while ASIAIR is applying a correction.
In short, all is good, as far as I can measure.
Chen