Hi Andrew-
are your spacings correct between
the coma corrector reducer and your camera sensor?
I had to use this to adjust mine to get it right:
Baader VariLock 29 T2 Extension Tube - 20-29mm Length
as per here:
https://www.flickr.com/photos/247194...in/photostream
How are you collimating the Newt?
An f4 mirror is critical for collimation.
I also have an 10" f4 Newt.
I use a laser in the focuser attached to a 2X Barlow and look
for the reflection of the paper reinforcement on the center of the primary
mirror in the 45 degree window -
I adjust the 3 screws to see the shadow of the paper reinforcement there.
That makes it an easy 2 minute job.
cheers
Allan