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I have used the AT66Ed which is the earlier model to the AT72ed.
Overall very good. I do get some differential flexure. But if I limit exposures to 10 minutes it isn't a problem but it does limit the length of exposures.
I use a diagonal so I can get to focus. Perhaps that adds to flexure.
Focuser is good not perfect. It can lack grip and slide if not tightened.
Also the focuser has a rotator which could add flex. Try to keep it tightened up as well.
But I can always get a guide star and 10 minutes at 1260mm gives round stars so its pretty good.
I mount it using 2 Losmandy D adapters which fit onto a dovetail plate on top of my refractor.
Its a workable system but limited.
Offaxis guiders are fussy but give better results as they don't suffer from flexure.
If you are using short focal length you can use a camera lens or an SBIG Efinder and fix the camera and efinder to the front section of the OTA's dovetail plate. That works too but probably only for short focal length.
AP sell a 900mm "cheapish" refractor and rings as a guidescope. No doubt it would be a good setup.
I bought a Vixen 95LMC as a guide scope as that is 1000mm focal length. Problem was I had trouble finding guide stars. Perhaps the 110mm LMC may be better as it has a bit more aperture. These are quite light and relatively inexpensive.
Greg.
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