Alignment with CNC Tube rings

[afm038]

Hi all,

A simple question but maybe not a simple answer........ I wish to put 2 scopes on a ADM dovetail plate both mounted using CNC rings (William Optics variety) - how do I manage to get good co-alignment between the 2 scopes ?

The misalignment is probably a couple of degrees and I've tried simple things like shimming with bits of card but to no avail, maybe a case of ditching one of the scopes CNC set of rings and replacing it with a set of ADM 3 point tube rings ?

ATB, Andy

[Merlin66]

Do you mean an ADM dual bar? How are you trying to fit two scopes on the one dovetail???

A photo may help..

(I made a dual bar to hold two vixen dovetails and got them aligned...)

[afm038]

Thanks Merlin,

Ok for plate read bar and please allow for my (mis) use of the terminology. The 2 scopes will either be mounted side by side direct onto the GEM mount or perhaps piggybacked together on my SCT, either way how do you get them to align with each other when there is effectively no adjustment on the CNC rings ?

I also could not to get good alignment using a single scope piggbacked using the ADM MDS system and WO CNC rings.

ATB, Andy

[Merlin66]

A couple of things...

What alignment accuracy are you looking for? For the same object to appear central (or in the same CCD FOV) between the scopes?

(You can use CCDCalc to check the different FOV)

How are you mounting the rings?

The "usual" method is to mount the rings on a dovetail and then clamp the dovetail(s) in a couple of saddle clamps which are fixed to a dual bar. This gives best support to the OTA's.

(If you need to shim the rings, cut pieces from an aluminium can work well!)

My first dual bar was made from a 100mm x 10mm piece of aluminium bar fitted with two Vixen saddle plates.

The Left/ Right adjustment I could get from the fit of the saddle bolts to the plate... the Up/ Down adjustment was made using the two small "Cone Error adjustment" screws fitted below the ring attachment on the Vixen dovetails.

This was enough to get both OTA's aligned.

I now have a GEOPTIK CNC machined dual bar which is very accurate and aligns the two scopes perfectly parallel. Any residual Up/ Down "error" is corrected with the Cone screws.

Geoptik Dual saddle plate - Vixen Synta & Losmandy :: Mounting hardware :: Altair Astro

The image shows my 6" f3.6 Cometracker and the ED80 on the Dual bar.

Hope this helps.

[perfrej]

I agree with the above. A properly machined dual bar thing should be right from the start. The small misalignment that can occur should be within the tolerances of the holes to screws, and can thus be compensated for that way.

/per

[Jessun]

Here is a simple Geoptic dual plate setup. I agree with Merlin66 that it is spot on parallell.

The CNC rings don't offer much apart from looking good.

[afm038]

Thanks for the feedback,

I was looking for pinpoint accuracy but maybe this is unrealistic ? I already use CCD calc to get some idea of object sizes on the CCD FOV for the camera's and scopes.

I'm using ADM mounting bars and ADM MDS clamps attached to the rings. There seems little or no adjustment on any of the attachment screws as they are all tight.

Given what Jesper says regarding no extra benefit it may be easier to dump the CNC rings and use a set of ADM 3 point rings as I've tried unsuccesfully shimming with card (don't fancy using metal shims as it may damage the CF).

ATB, Andy

[martin_h]

I use the ADM dual bar setup and found I can adjust both scopes to centre a star at the same position....see images, I use 1 screw in the slot part of the bar, that way I can get some lateral adjustment, for elevation adjustment I use slivers of plastic(old credit card) under the rings.

[Merlin66]

As Martin said, the shims, if you use them, go under the rings - nowhere near the CF OTA??

Can you upload an image of your set-up??

[martin_h]

I set one tube up as normal, then "toe" the other in to match. Centre one scope with a star dead centre of my capture screen, then adjust the other to match, close enough is good enough........Registar is your friend here.

[afm038]

A misunderstanding here on my part I thought you were inferring that the shims went between the rings and the OTA hence my concern with a CF tube, I see that is not now the case.

Here is picture of the WO CRC rings on the ADM bar mounted on the SCT Homeyer cradle, I don't have one (yet) of the dual bar setup.

Andy

[Merlin66]

Andy,

On this arrangement, the shims, if used, would sit between the ring(s) and the ADM Clamp blocks. Fine adjustment left/ right; on the mounting screws of the ADM minirail or the radius blocks.

[afm038]

Many thanks to you guys.

I'll have a go as you have suggested, however it's extremely time consuming and a right pain to have to repeatedly remove it all from the scope to access the screw that holds the clamp to the ring, shim it and replace it on the rail. The fallback of 3 point rings starts to look ever more suitable.....

Andy