All modern Vixen telescopes come with a standard compression ring for the draw tube which features simple thumb screws which will scratch/mark whatever 2" item (eg diagonal, extension tube etc) you put into the 2" focuser.
To stop this Vixen make an upgrade compression ring
http://www.myastroshop.com.au/produc...sp?id=MAS-080A
Bought this but then never wound up using it - essentially BNIB
Asking $50 inclusive of standard postage anywhere in Australia