[erick (Eric)]

Good to hear Bob.

Yes, I hear people saying that screwing up the locking screws just pushes the primary mirror back out of collimation.

In my view, if the collimation stays pretty close as the tube is moved from horizontal to vertical, all is fine and leave the screws off the primary miror cell. If the collimation moves, then solve it another way, rather than trying to use the locking screws. Seems there are two approaches with the GSO. First, replace the springs with stronger ones. Second, put the existing springs under greater compression by using the three collimating screws to pull the mirror further down the tube - a good centimetre or more will help. The only possible downside (as I discovered on a Bintel BT-402 I did this to last week) is that the small GSO plossls might no longer come into focus - the focusser bottoms out in its travel prior to focus.

I've been fortunate not to have any problem with the trunnions on the 12". They are firmly in place. I did tighten them on the 8", but I could reach down from the spider end to hold the nuts.

On my 12" GSO (and my 8" GSO prior to that), I have only tightened the locking screws for transport.

Yes, I have used both my GSO 2x Barlow and my TV 3x Barlow for barlowing a laser collimator. My approach is to use a piece of paper or card with a hole punched in it (just your regular hole punch), hold it inside the tube at the bottom of the focusser, allow the barlowed laser beam to pass through the hole, and the reflection of the centre "spot" appears back on the paper. I have to admit that I've only ever put the barlow in place after I have set the collimation with the un-barlowed laser and never found I needed to adjust it further.