[JohnH]

You will still have some coma on a C9.25, less, sure but it is there, the refractor suggested will also suffer from this, you can crop to remove it of course...

The flatest fields I know of (at reasonable $$$) are the Meade R series and the VC200L, you might consider swapping appature for flatness - imaging does not require big scopes for great results (eg ED80!). The C9.25 is very highly rated for planetary and imaging work and was on my shortlist (Meade R was not out at the time)...SCT folks still seem to have to play with collimation a fair bit plus you have the corrector plate (and associated dew and cooldown issues).

The VC200L has an industrial strength spider - and I have not had any need to tweak mine (yet)...it has a very flat field, open OTA, a fixed mirror...just about optimised for imaging. Is it perfect - no - the central obstruction is large as are the spider vanes reducing contrast/details on planets, the rack and pinion focuser is not great and the focus lock causes image shift.

There is another problem with any of these - they are all about F10 so your tracking will HAVE to be much better to get round stars - you will need a focal reducer.

This is a tough hill to climb im my experiance...