Does your focuser mount to the hole or to the flat side of the tube. Most go to the flat side of the tube so a slightly larger hole won't matter.
If the focuser mounts to the hole, epoxy (like JBWeld) can be used to shrink the hole as necessary and you may want to build a dam to hold the epoxy in place. In addition, you can also epoxy a plate inside (or outside if you have height problems the other way) the tube and drill the right sized hole and mount the focusr there.
I assume that you have a 1.25" focuser as the 2" ones will need a hole larger than the 2" hole you have.
If you feel the need to close up the hole, epoxy in the space will fill that need quite well after you have mounted the focuser.

• Thanks - jimbop - January 5, 2004 - 23:15 UTC