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Paul
If you are using the VC200L perhaps you should look carefully at the drawtube end where you insert the 2" nosepiece which has the 60mm-to-50.8mm diameter black ring with the 2 thumb screws - This I think is the weakest part of the Vixen focuser and is very dickey!!
When I first got started into imaging I was frustrated over the many failures with my many attempts which was caused by movement in the manner you described - even after checking for flexure and everything else including changing the mount which didn't solve my issue.
I had by chance handled the 5D one night whilst it was already set up and it wiggled slightly; mind you ever so slightly and I thought that it might be worth looking into because no matter how tight the 2 screws were the camera still wiggled slightly - had machined out a replacement ring out of brass with a tapered wall surface and a mating split ring that slipped over in the middle and was locked into position by a threaded cap-like cover ring which when tightened applied pressure onto the split-ring which closed tighter and tighter around the nosepiece because of the tapered surfaces (sort of like an olive locking principle used in plumbing joints) - and my troubles disappeared - I'll have to look for the pixs to give you an idea of what I'm talking about if you think that this might be the likely cause, can't remember where I saved them but I can take new pixs, np!
The flip-mirror 2" nosepiece with the very slight "safety" undercut is not very stable either when locked on that black ring and you can imagine that as the scope pans the sky over the period of imaging the transitional changes with the weight hanging off the end will shift along and it would definitely result in issues
I don't have the wiggling issue when using the focal reducer because I use the original Vixen Canon Wide Adapter and as you know that black ring is taken off because the focal reducer is screwed in its place instead and then the CWA which has 3 thumb screws and very solidly holds the camera - don't know whether when using CCD (as I haven't yet used one on the VC200L) is different experience or all the preceding I've posted is OT (and I do apologise if it is)
HTH
Cheers
Bill
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