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OAG Help - will this fit with my basic setup?


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Hi all,

My setup consists of an NEQ-6 with a Skywatcher 80ED-DS + .85x Focal Reducer. 

I tried to guide using the 9x50 finderscope that came with the telescope kit (worth about £50) and a ZWO-ASI 120MM CCD camera. I went for 10 minute subs, and verified this wasn't pushing my polar alignment by sticking around for the first sub to come in, and hooray, pin-point stars. So I set it up to take more exposures for the next couple of hours, went and had a brew and put my feet up.

I've come to inspect my subs, and have found almost all of them have some kind of minor error. I believe it to be caused by differential flexure, and so am looking at the possibility of using an OAG instead. I have my eye on this specimen: https://www.firstlightoptics.com/off-axis-guiders-oag/off-axis-guider.html which seems to be well-suited to my needs.

My problem is, the adapter jargon is a little scary for me. My thinking is to attach the OAG after the focal reducer, which FLO have verified the OAG is designed for, and then attach my guide camera to the off-axis. I understand the need to focus the guide camera, so I was thinking I could attach one of these between the two: https://www.baader-planetarium.com/en/baader-focusing-eyepiece-holder-1%C2%BC%22--t-2--(t-2-part-08a).html and my question is, will this work without the need to buy any more adapters? I'm pretty new to this and this is pretty much a sanity check before I throw away a hundred pounds because of my own ignorance.

Thanks for reading :) 

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Hi and welcome to SGL

If you have the finder still mounted in the original fitting then mounting it more solidly wouldn't cost much.

A piece of aluminium bar fitted on top of the tube rings and the finder scope mounted in some pipe clamps would sort it.

Something like this.

https://www.ebay.co.uk/itm/Rubber-Lined-Munsen-Rings-optional-Backplate-Pipe-Hanger-Clamp-Bracket/272485561823?hash=item3f7167b5df:m:mL9qnVHsKBV9IgW8amZ3poA:rk:18:pf:0

The OAG is a bit overkill for an 80mm refractor.

Dave

Edited by Davey-T
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Cheers for the suggestion. I'm not entirely sure how I would go about fitting one of those though. I can see that in the top of the tube rings there are two holes, would that have something to do with it?

I agree the OAG is overkill, but I'm looking at it with a bit of futureproofing in mind, as well as avoiding the problem of the wee finder dewing up (despite a dewshield). Is it definitely not worth getting an OAG here? It would be quite reassuring to be able to slap one on the end of the scope with the assurance any flexure in my setup would be eliminated.

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I think whatever scope you use, the best way to guide is through the same scope as you image through, so... off (or on) axes guiding is always the best,
less weight, (no second scope), no differential flexure and most of the time cheaper.
If that OAG is kind of dedicated to your focal reducer as FLO said, it should be fairly easy to get things working well. Whether you will need an extension yes or no, depends on the back focus of your camera's. Your guide camera just screws on to the OAG, so that expensive Baader piece is not neccessary, but maybe a little extension will be needed,  depending on the backfocus of the camera's as said before.

You don't mention those, so I can not give any advise on what you probably would need.
Orion has a very nice OAG as well, with a lot of options: https://www.telescope.com/Orion-Thin-Off-Axis-Guider-for-Astrophotography/p/102812.uts
as you can see the set includes two extension rings, so quaranteed focus.

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