Tonight, I tried to use the Borg 45ED II with reducer and extension tube, focusing was done by far away terrestial object and it's so close to infinity so that when I slew to the sky, I could immediately see pinpoint stars. After slewing around, I managed to get M42 in the view. Fine tune the focus with trapezium, and I've now taking images.
A series of shots taken with 548 gain and 2.872s exposure were conducted as the core.
And then a series of shots taken with 648 gain and 19.472s exposure were obtained as the extended location, limited by polar alignment accuracy inside my home.
Photograph of the setup:-
Push a bit more:-