Focusing Problem

Hi, I'm into astrophotography, and love my 10" LX200
HOWEVER!!!
I can never seem to get that perfectly clear focused picture that I expect.
Can anybody make any suggestions?
I am aware of knife edge focusing, and I have tried it...but I don't get it.
When I have the telescope out in the field, and I have a bright star
selected, and I have my knife edge in place, what do I do? Am I supposed to
slew and adjust focus back and forth? Is that the technique?

Malcolm Park
Toronto Ontario.
http://www3.sympatico.ca/malcol/b1a2r3b4.html