Before I perform surgery with hacksaw on the tube of the 100ED I thought I would take some pictures to establish the amount of shortening.
Here is one result. With shortening will get more focal reduction.
Details. Canon 5DH in cam. noise reduction on,100ED with Hutech FR/FF so at 765mm @ F7.65,Hutech nebula filter, 5X8min ISO 800, stacked with Registar. Only adjusted curves in PS, no other processing! Vignetting is only a tiny bit at the corners thanks to a 2.7 inch focuser and removing the rear baffle of the 100ED which was causing vignetting!
Larger picture 750k
http://users.bigpond.net.au/avandonk/Car_100ED.jpg
This was the only viable target with the Moon out.
Bert