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Off axis guider


johnrt
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Looking at buying an OAG, as my 150p is on an EQ5 so won't really handle the weight of a guide scope.

I've looked around a bit and narrowed the choices down to two options. Either;

Orion Deluxe

Orion Deluxe Off-Axis Guider

I'd like any info anyone has with this one in terms of back focus in the 150p using my 1000d DSLR. Will I have focusing isues? Also can I connect the camera to it with just the T ring?

Or,

TS Off axis guider (with EOS fitting)

Accessories @ Modern Astronomy

Which would you buy?

Edited by johnrt
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I have a few OAG's...

The Orion is very good but will require at least 55mm backfocus.

The TS appears very narrow but... you may need to add spacers to the imaging camera to get the guide camera into focus...

For Newtonians the one I'd recommend is the Lumicon Newt OAG.

Short body length, 2" attachment and a big pick off prism.

Ken

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I have a few OAG's...

The Orion is very good but will require at least 55mm backfocus.

The TS appears very narrow but... you may need to add spacers to the imaging camera to get the guide camera into focus...

For Newtonians the one I'd recommend is the Lumicon Newt OAG.

Short body length, 2" attachment and a big pick off prism.

Ken

Do you think I'd be able to focus at all then with the Orion, and if so would it rule out other accessories down the line if I wanted to add a coma corrector or something similar?

Where do I measure the focus distance I need to have available? Would it be from where my camera currently focuses at?

Lumicon looks an interesting alternative to the TS - similar price too.

Edited by johnrt
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Measure the distance from the current focus to the hard edge of the focuser body... if this is less than 45-55mm you may have problems ( with any OAG)!

Obviously the problem of back focus becomes worse when you consider adding reducers/ correctors/ filters etc etc....

Ken

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From what I can see my standard crayford focuser only comes out about 55mm in total from the body, so I'm guessing that rules out the Orion for me.

Would be good to find someone who had had a go at autoguiding on a skywatcher 150p, I've searched around various places and can't seem to find anyone who's tried it.

Edited by johnrt
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Ken....

I have an Atik 314L in use with a WO72. However I will need a 50mm extension tube to gain focus.

Do you kknow if using the Atik OAG will eliminate the need for the extension tube?

Thanks

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The ATiK OAG hasn't been released yet, so I can't comment....

The issue of the imaging camera spacer is really related to the guide focus. If the imaging CCD camera only needs a backfocus of say 12mm and it's mounted directly onto the back of the OAG body ( whether an Orion/ TS/ Lumicon etc) it will be almost impossible to get a conventional guide camera ( QHY5/ Atik16/ DSI etc) close enough to focus on a guide star.

The narrow body TS OAG is designed for use on a DSLR body which is 55mm backfocus and gives enough room for the guider.

A perfect technical solution would be to incorporate a transfer lens system in the guide take-off which would allow a degree of independence between the imaging camera and the guide camera. You could then do away with spacers etc etc.

A bit rambling...but hope this helps,

Ken

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Thanks Ken.

This is all a bit complicated to me :headbang:

Would be nice if there was a site that broke down all the info of sizes with various set ups. As it is I just dont know what I need, or even if its possible with my set up.

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I received an email back from Telescope Service who said;

As far as I recall the Skywatcher Newtonians have an exotic adaptation on the focuser. At first the focuser goes to a diameter that is larger than 2", then there is an adaptor from this larger diameter to 1.25" and another adaptor to 2". Both of these adaptors are about 40mm in length. Can you confirm this?

If this is so we have a problem. If you use the 2" adaptor then it is much too long, so you won't be able to reach focus. If you don't use the adaptor then you don't have a standard adaptation, so in turn we do not have any adaptor that would connect the off axis guider to the telescope.

So that pretty much rules out using an OAG.

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Arran,

Just re-read your post....

If you're currently getting the Atik 314 to focus with a 50mm spacer in the chain, then yes if it was removed and replaced with an OAG body, you'd come pretty close.

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Thanks Ken

How will I be able to find out if a QHY5 will work as the OAG in this set up?

Seems a bit crazy to buy an OAG in the hope it will work, but I cant find any literature to work things out.

Edited by Aza
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Arran,

You can download the Orion documents/ manuals from their site.

The QHY5 will work with almost any OAG - It's worked on all the ones I've tried.

Just a bit of fiddle to get the correct spacing.... but this needs to be done once only for your imaging camera.

Ken

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Not exactly your setup, but these notes may help:

Set up your OAG and telescope/camera in daylight. You may need to use a very fast exposure time on the guide camera if it is very sensitive, otherwise it will overexpose. Focus the imaging camera, then adjust the guide cam focus until in focus.

This was my experience with the OAG:

Orion OAG First Light

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Thanks for the offer Ken :headbang:

I have just gone ahead and ordered one.

Thanks for all the help, hope you dont mind the questions, but here is another one :p

Where in the optical train would you put the OAG, in relation to the imaging camer, filter whee and williams reducer? I am sure this will be more obvious once I see all the gear.

Thanks for the link blueastra I shall take a look now.

Edited by Aza
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Don't know what the optimum design back focus distance is for the reducer... this would normally take precedence over everything else.

I'd go for the OAG infront of the filter wheel if possible; then if you use narrow band filters you still get a full brighness guide star.

Ken

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I use the Lumicron low profile OAG and it works very well, abeit with a Refractor so travel isn't so much of an issue.

It is recommended for the Newts, but the one from modern in your 2nd link is a better one by all accounts.

I got my Lumicron OAG from Rother Valley for about 200 notes delivered.

Focusing is a pain in the butt, but works when you get used to it.

I use a QHY5 as well.

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  • 1 year later...

Any more experiences with the ATIK OAG?

It's now available through FLO, as there's positive noises here on the job extension I could be looking at a 8300 based camera and OTA with the 16ic attached.

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