Chroma Key Green (Keylight) HDV footage

Hi there, I'm a bit of a newbie studying my HDV footage and Keylight on AFX. I got a green screen and I've done some tests using that cineform codec. In my results, however, although my screen mat shows a pretty nice key (pure white in the centre), still when I render the video, I see a lot of "fluctuating and dancing pixels" on my subject! Clearly that is unnacceptable. Do you know how could reduce that? Do you recommend more light on the subject? or standing further from the screen? Or should I be trying to get an "SDI Capture" for better results. I have Sony FX1 camera. Is it even possible to do an SDI capture with this kind of camera?

PS...I already know that compressed video doesn't make a good key but am trying to get the best results with what I've got.

Thanks,

April