Thanks for your thoughts Rick & Tim.
I should have mentioned that I'm using a .8 flattener/reducer here as well,
Here's another starfield I shot same night that may be more useful, it's
60secs LUM only.
https://www.astrobin.com/337564/
Rick I don't have a Bhatinov mask - but I'll be ordering a laser etched one soon.
Tim, I'll try your suggestion with a defocused star field with a bright central star tonight (if it's clear at the star party at Snake Valley!) - I have the 2.5 inch focuser and the tilt ring.
I'm reluctant to fiddle with the focuser as it's meant to be collimated at the factory?
What's the primary baffle tape-fix to stop the primary mirror moving please?