Coma occurs in many optical combinations, mirror, lens, cat.
This is why you get field flattners. Normally the lower the f ratio the higher your coma, but some scopes have correctors built in to fix this.
Coma has absolutely nothing to do with the camera. But for the size of the sensor will show any coma in you optical train, because the light has to now reach further away from the centre to reach the edge and thus starts your problem.
I use a MPCC for my 22" and it does a great job.
To learn more about it, go here
http://www.astrosurf.com/luxorion/re...errations2.htm
Theo