Hi Bill - sorry for the delay in replying but I was off at a small star aprty. Poor skies we think because the wildfire smoke has now reached the other side of the pond. Amway the way the Mark II works is that there is a small ring that screws on the front of the focuser tube, perhaps about an inch long but I need to measure it, and then the filter slide fits over that. I would imagine with something as fast as your scope that some vignetting may well happen. I don't see any with mine but then it is F4.2

Owen