[alistairsam]

Hi Rodney

You need a coma corrector, field flatteners are used in refractors to fix the curved plane and an EOS camera or ccd camera doesnt change what is required. You have a much larger sensor in the 600d so deficiencies show up more than the dsi.

Is this cropped, I'm surprised at the relatively minor coma if this is without a cc.
Usually an f3.9 reflector would have much more severe coma, but isnt the f3.9 ratio a resultant of the coma corrector that Orion provide? Native focal ratio is F4? So isnt there anything in front of the 600d?

Have you checked collimation?

Regardless, that is some nice detail you got with just two subs.
And if the camera is not modded, you don't need an IR block as the camera has it already.

Cheers
Alistair

Edit: i'd suggest using ISO 400 and with the filter wheel, make sure spacing from the camera sensor to the coma corrector is as per spec of the cc.
You could start a thread in the equipments section to ask questions about the different bits and issues you might have.