GSO 12" RC Truss Secondary Mirror collimation screws

[brisen]

I have just received the GSO 12" RC Truss and checked the collimation and it is very close, the laser falls inside the circle on the centre of the secondary but is just off to the side of the circle a fraction and probably doesn't need to be adjusted.

In attempting to loosen the screws to move the secondary, I cannot get them to budge at all. It is like they have been given a dose of Loctite at the factory. So far I have just tried the allen key and hand pressure to try and loosen it. My next option is possibly trying something on the end of the allen key to try and give some more leverage but I don't want to use too much force in case something I don't want to move, moves.

Has anyone been able to get these screws loosened and if so how? Now I understand why it held its collimation so well, there's no chance of them moving in transit.

I can't test the collimation with an image as I need to get another set of the M117 extension rings to even bring the CCD close to focus. Does anyone know if these are readily available in Australia or if they have to be ordered?

Brian

[Marke]

Probably can't move easier to add a tilt plate and adjust the focuser to align the axis

[brisen]

Thanks I will have a look at that option.

Brian

[Marke]

Easiest fix just because the laser isn't hitting centre of secondary most likely reason is a little focuser tilt I would never move the secondary personally

[Paul Haese]

The screws are tightened up for travel but can be moved with a bit of brute force. Try using a set of vise grips along the small end of the Allen key. Then undo anti-clockwise, the screws will make a crack sound and then will freely move.

Owning one of these scopes requires collimating them. If you don't have one, get yourself a Tak collimation scope. Use the laser to set the camera centring plate at the rear (just around the adapters) to land in the centre of the secondary ring. Then use the Tak scope to collimate the primary to the secondary and the secondary to the primary. Check with the laser to check the focuser position again. Do this until everything looks correct. It might take several iterations. On the drawing H is the secondary shadow, move the rear collimation screws (two screws one large and one small near the air vents) to centre that in the Tak scope. Then use the secondary screws to centre the B. Don't use the secondary screws to centre the laser in the ring on the secondary. You need to use the camera centring plate for that.

[brisen]

Hi Paul

Thanks, this is helpful. I will have a look at the scope once I get a chance again. The Tak scope is next on my list to get. I haven't seen any locally so assume the US is the best option.

Brian

[jwoody]

Hello Brian#
I got my Tak scope from AEC.
https://www.astronomy-electronics-centre.com.au/
They aren't cheap make do make life pretty easy around RC's.
Jeremy

[brisen]

Thanks Jeremy. I will get in touch with them.

Brian

[brisen]

The Tak collimation scope arrived this morning and I have managed to collimate it and get the circles fairly well centred with the reflection of the spider also lined up. I am going to have to fiddtweak it a bit more as one side of the large circle is not quite centred but it isn’t sitting off to the side and there white space around it. Now I just need to get the whole setup out of the garage to star test it.

I got my hands on a set of T handled Allen keys from Bunnings and that made it much easier to loosen the screws and less risk of me dropping the Allen key.

Brian

[jwoody]

Glad to hear you have it sorted.
Clear skies

[Paul Haese]

Brian, you should be able to get the collimation very close with the Tak scope. Make sure you check your focuser to secondary spot first with the laser. Good to hear you have nearly got it sorted though.

[brisen]

Hi Paul

Thanks. I have added a tilt plate between the extension tube and the focuser and tested it with the laser before I attacked the collimation yesterday. It was out and I have adjusted the tilt plate to get it in the centre but didn't think to test it again after I have been collimating. Hoping to drag it out tonight and get setup since it is supposed to be clear. I will use the laser again to see if it is still centred and adjust again in case it has moved.

Brian