Well, I put further testing on hold for a few days as I was involved in another project. However, got out on Friday (04/03/11) with the 102. Even with the focus tube fully extended, Sirius would not come to focus. Solution: a T2 extension ring from FLO fitted between the scope and the camera. Going to go for the biggest (40mm). Even with the filter wheel fitted (when I get round to that bit) the total increased distance will be less than the range of the focusser, so I should get maximum flexibility without running into difficulties of not having enough 'in-travel'.

At least, that is the plan ...