Thanks for the comments. I've adjusted levels to remove the noise - it didn't remove as much of the object detail as I thought and probably does more justice to the DSLR
. I'm not yet ready for a dedicated CCD and at the moment I enjoy squeezing the most I can out of the 550D and Dob and its ease of setting up and imaging. And from the same camera I can do wide field as well (attached is 10x4sec exposures at ISO3200 at prime focus).
Cheers,
Tom