[gb_astro]

Marcus as far as I know the displacement of the red concentric rings is not important.
It indicates a bit of slop or misalignment of the Tublug in the focuser.
but apparently this does not affect this barlowed laser technique much.
The Glatter laser and Tublug is a long and heavy combination and I guess it will sag in most focusers.

Centring the shadow of the donut is the important thing.

You should find that you can centre the red concentric rings by
pushing the laser/Tublug around a bit while it is in the focuser.
At the same time you should see that the donut does not move much at all.

gb.