I have finally got my Meade SN10 to have a flat distortion free field for the full frame Canon 5DH. I have fitted a Borg helical focuser and bits including a filter box. Once aligned (by eyeometer) I got the result below. Four minutes at 400ISO jpg straight out of the camera. The thing that makes the field flat and coma free is a Tele Vue PLU-1106 Paracorr.
Full res image 500k
http://members.optusnet.com.au/~fmlee/IMG_0018ps.jpg
Bert