That is a test shot again, and now I am pretty sure now the issue of why bright stars look a bit weird is caused by the LPS filter installed in the camera body was not so perpendicular to the optical axis.
Date & Location: Jan 2nd, 2014 @ PTC
Imaging scope: Vixen VSD100 F3.8 astrograph
Camera & Settings: Modified 100D + LPS @iso1600 & iso400 RAW
Effective focal length & F-ratio: 380mm F3.8
Total exposure: 12x60s @iso1600 + 5x300s @iso400
Mounting: Vixen Modified GP2 photoguider
Guiding: 50mm finder-guider + QHY5 + PHD
Air steadiness: 4-5/10
Air transparency: 5/10
Air temperature: ~14.5C
Humidity: High (>90% as estimated)
This final image was a stack of two sets of different exposure at different iso speed and without any dark calibration. Though a flat field was applied but that obviously it was not a good one. Only very simple and basic adjustment in PS with Level and Curve but finally it comes out I think to be ok for looking.Hope having good sky soon for doing it again in Lantau Peak.
How does it look on your monitor? Thanks for your looking and feel grateful if having your comment.