Collimatable star diagonal?

[garymck]

Is anyone aware of an easily Collimatable star diagonal? I have a Skywatcher and a GSO, and they are both significantly out of alignment. The GSO is much worse than the Skywatcher. I know they can be fixed by shimming, but that is really tedious. Looking for something that has adjustability built in...

TIA
Gary

[Merlin66]

Gary,
Never come across a diagonal which could be re-collimated.
I think the nearest you'll find was the Meade Flip mirror (in both the 1.25" and 2" sizes). These had excellent 1/10 wave full thickness mirrors mounted on an adjustable shaft and a stop fitted to refine the actual "flip" of the mirror.
https://www.mta.ca/uploadedFiles/Community/Academics/Faculty_of_Science/Physics/Gemini_Observatory/Observing_Resources/meade-flip-mirror-647-operating-instructions.pdf

[astro744]

The Tele Vue diagonal is single piece body construction and according to Tele Vue, "Permanent alignment is assured" See https://www.televue.com/engine/TV3b_page.asp?id=62&Tab=_90EB

There is a 2" one in the classifieds otherwise Bintel.

[Outcast]

My GSO dielectric is 'shimable' with relative ease but, only the teeniest smidge out whereas my Meade S5000 dielectric was bucket loads out & a right royal PITA to shim...

I'd be interested to know if there was a truly adjustable/collimatable diagonal...
& I'm leaning towards a BS call on Televue on this one...

[glend]

My GSO Diaelectric has four threaded holes in the bottom, which i have always assumed were for collimation adjustment, else why have them there.
I would ask how you actually checked the diagonal collimation? I believe it can only be done with a laser (which itself was collimated). Many lasers are not perfectly collimated as a rotation test can confirm).

[Rainmaker]

The Baader BBHS 2" is collimatable using the push pull screws in the base.

[Merlin66]

Matt,
Reading through the Baader documentation on their diagonals I was unable to find any reference to the ability to “re-collimate” the mirror.
Can’t you give me a link to the info????

[Outcast]

Laser that had been checked for collimation & flat mirror... I'll have to re-check to see if mi GSO has these 4 holes.. can't say I ever actually noticed, thanks Glen

[Rainmaker]

Hi Ken,
I don't have the info.... I have the diagonal here and have actually recollimated it a few months back.
The diagonal's hard silver coated mirror is bonded to the back plate and each corner of the diagonal's back plate has M3 grub screws for 'push' and M3 cap screw for 'pull'.

This one was slightly out of collimation in that my 2" Glatter laser's spot ended up being 7mm off centre.

I first tested the focuser alignment by removing the diagonal and using an extension tube with the laser, this placed the laser spot on centre. I then removed the extension tube and inserted the diagonal to see that the spot was now 7mm off towards 11 o'clock, I then adjusted the 'push/pull' screws to centre the spot on the objective of the TMB-LZOS 152. ( I used a circle cut from white paper with x & Y axis marked and centre that over the objective)

[Rainmaker]

Baader website image:

[Merlin66]

Matt,
I did see that image, but there was no mention of collimating the diagonal.
Based on your work, I think we have to acknowledge that there is provision for collimating the diagonal.
Thanks for the info.

[garymck]

Thanks for the replies. I checked the collimation by comparing the spot from my Glatter Laser with and without a star diagonal in my ED150. The GSO diagonal put the spot about 40mm off centre, the Skywatcher one put it about 15mm off centre. With no diagonal the spot was centred. Can't afford the expensive diagonals, so will have to shim :-( The GSO has 4 tapped holes in the base, but putting screws in these will press directly on the back of the mirror (held in place by the back plate pressing on a thin layer of foam). Almost certainly will cause astigmatism...

Gary