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So far this thread has had a visual focus, however I'd like to add a twist. Don't automatically assume that a SCT (or for that matter any scope that requires collimation) which is well collimated visually will perform well for astrophotography (either planetary or DSO).
To get the most out of a scope for imaging you should be collimating with the imaging train in place. Failing to do so can result in significant FWHM and HFD variations as I found out... I used CCDInspector on the 11" SCT I had around 13 months ago. Visually, the collimation was good. Plenty of detail resolvable with focus snapping into sharp contasty views, but when I attached an imaging train results were less than optimal. As it turned out, not only was the collimation out, but so was optical axis squareness with the camera. As camera chips are flat any form of optical curvature has a negative effect, hence the reason why you pay high prices for scopes that have native flat fields. Unfortunately I didn't keep my pre/post CCDInspector graphs to show the results. Still got them for the FSQ (which I'm still battling with curvature probs, but that's another story).
I have simply raised this as for awareness. I wouldn't bother going to the extent of camera orientated collimation if a) you're only doing visual work b) not worried about achieving the highest image resolution possible.
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