Hi Fintan,
After much browsing of the web i am noticing that all DSO photography is done with apochromatic refractors, generally in the range of 80mm - 110mm.
Here is a litte gallery, just to make you drool some more
. (The guy posted on the AstroTrac Yahoo group I am member of, although the images are not taken using an AstroTrac).
picasaweb.google.com/Yuriy.Toropin/AstroPhotosNikonD50
All I can say is, wow :shock:
/Mikkel