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OAG with Newtonians

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Hi All, just after some advise, I've just bought from Starflyer (Thanks very much) his Orion Optic UK VX10 as never having owned a newt before, I wanted to have a play before committing to something much more expensive.

I need to buy a Coma Corrector and there are various ones suggested from Baader and Skywatcher, for the under £200 bracket this one comes out tops, I'm just trying to work out the backfocus as I want to use an OAG with it.

Now Skywatcher suggests a backfocus of 55mm which is perfect for my Moravian setup and FW, however, how will I be able to squeeze an OAG into the imaging train and maintain the 55mm, the focuser is a Baader Steeltrack clone as per the picture: -


Does this mean I will have to use a Guide scope rather than an OAG?

Any thoughts would be most appreciated.

Many Thanks.

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You should be able to do it, though of course depends on the individual components you have. I managed it with a similar setup and although there isn't much space to play with, it can be done.  You will need a fairly low profile OAG, the one I have is only 16mm thick and the coma corrector will need to be inserted into the focus tube. 




spacing diagram 2.jpg

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Thanks Steve,

As you can see in the picture I am already at 55.07mm without an OAG fitted, add 1.0mm for the Chroma filters and I am just over 56mm, you'll have to excuse my scruffy drawing.

Now I can exchange the front adapter so that it will accept the Moravian OAG which I specifically bought to use as it keeps the backfocus at 55mm, but to be honest the Moravian OAG is a pile of pooh, that's why I use the Celestron one as it really is very good, but far too big to use with a 55mm constraint.

What OAG are you using to keep the distances down as it might be worth getting an adapter made if the OAG is narrow enough.


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4 minutes ago, alacant said:

Hi. Use the GSO coma corrector instead which gives you 75mm of back focus. Your Celestron will fit easily.


Thanks for that, yes, that is excellent value, how good is it at removing the coma, as I looked at the Baader and the reviews weren't brilliant, I saw a side by side of the Cheaper SW and the SW f4 Aplanatic Coma Corrector and it was like chalk and cheese.

I think even the Celestron will be too big as this is what the dimensions are listed: -

OAG Body: 29mm
Male M42 and M48 camera adapters: 12.5mm
Female M42 and M48 telescope adapters: 4.5mm
Short T-thread Spacer Ring: 6mm
Medium T-thread Spacer Ring: 11.55mm
Long T-thread Spacer Ring: 24.25mm
Medium M48 Spacer Ring: 11.55mm

But with the GSO I might get away with a ZWO OAG as they are quite narrow at only 16.5mm thin https://www.firstlightoptics.com/zwo-accessories/zwo-off-axis-guider-oag.html

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