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[AggedorOfPeladon]

I have a Combo H-Alpha Quark and the Calcium Quark, and when I use them on my 120mm f/8.3 refractor (Celestron OmniXLT), I am having focusing problems.  Specifically, I can never get the image focused if I use a diagonal (2" or 1 1/2" no difference) and have to use it at the prime focus.  Even then it is not focused with an eyepiece, but my Cannon Rebel T3i, which always requires a change of focus from using an eyepiece), can get a sharp, focused image...with a whole 3 mm of travel left before the focuser is all the way in.  I don't have that problem with my Meade ETX-125.  To make things more confusing, Daystar talks about the Quark needing more *back* focus.  I've not read about anyone else having this problem.  So, I'm basically using the camera's live view as an eyepiece.  (Anyone considering a Cannon Rebel for astrophotography, incidentally, should definitely get the T3i, not the T3.  The T3i has a tiltable live view display which is infinitely more satisfying to use on a telescope than the fixed, flat T3 screen.)