Nice shot there mike.
With the 40d and dusty stuff i find that it needs 10 min of exposure to pick it up. I like you have the 40d with the mod, but mines a open mod with a screwin Astronomik 2" UVIR filter much better in my eyes!
http://s700.photobucket.com/albums/w...gmanandM42.png
Same image same composition (added MPCC for field flattening) only difference is this was taken in a bit of light pollution and 10 min subs!
Feel free to ask me anything you want with the 40d often you can pick up great info from others with the same equipment!
Brendan