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Just for the sake of accuracy I have guide scope guided my CDK 17 with a reducer at 1761mm focal length (the reducer bars the use of anything but a self guiding camera for guiding due to the lack of back focus) with good success.
So it can be done and I could easily tweak from what I had with a much larger T-point model, a more refined polar aligment using the Sky X and a supermodel.
But yes its a bit fussy for routine imaging and MMOAG leaves it for dead of course.
As far as getting a guide star with a MMOAG is concerned I routinely image with one on my CDK17 at nearly 3 metres and Sbig STi guider (lovely unit) and I usually have no trouble. It has happened a few times I had to reframe the image to find a guide star but usually the object was still not far from centre and plenty of chip real estate left to capture it.
If you setup a MMOAG on the main scope you also use that to guide the refractor when you use it. You simply leave the guide camera on the MMOAG and plug off the end opening where the CCD cam goes on the MMOAG and put your imaging camera on the refractor.
With a 300mm RC you will probably want to use Tpoint to get the required accuracy of polar alignment and a well done PEC curve to settle it down even more. Drift alignment takes you a long way but there is still some accuracy left behind that t-point can detect and refine the polar alignment even more.
Also I agree with getting the carbon fibre version. I think expansion becomes more critical with longer focal length scopes and especially RCs which are sensitive to the spacing between mirrors.
Greg.
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