Thanks Mike!
Yeah I know...
I think when Orion and Horsehead season rolls around (in a month or so) I will get the spacing right then. Not too keen at the moment to use up what imaging time I am getting on this. Plus, I am planning on adding RGB stars after removing them with Straton. So, I can come back to them next year
Or, maybe I should just bite the bullet and get the spacing right now...
EDIT: just went and stuck a 5mm spacer in. I think it has made a difference. We will see tomorrow when I put the bi-colour image together... Collecting OIII as we speak
SECOND EDIT: Thanks Mike. Adding 5mm made all the difference. Lovely and flat to the edges now. Thanks for giving me that ltlle push