Thanks Mike and Liz
Hehe, Mike, I see you already had this focus problem with a 12" gso newt
As the only way I have found to move up the primary is to cut the tube and I'm not sure to do that properly, I use a barlow 2x to pull the focal plan further out of the tube.
The counterpart is that focal length jumps to 3000 which is too much for the Moon.
There is maybe another solution, using a low profile focuser...