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balance problem with Onyx 80EDF

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#1 cruling

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Posted 16 March 2013 - 02:40 PM

Hi, everyone

I have a balance problem with Celestron Onyx 80EDF refractor.
I am using it with a nikon D7000 on a CG5 as my imaging setup, but the RA axis can not be properly balanced, as the camera need to back out about 2" to reach focus, so the camera end is heavier than the other end, and the dovetail on the scope is not long enough.
I think there are two ways of solving this, either put a mounting ring with a longer dovetail bar, or change the dovetail clamp on the CG5. I would prefer the first, what do you guys think? anyone has done this before, on 80EDF?

BTW, anyone knows what is the use of this part? I came with my CG5, but i'm not sure what's the use of it.

Thanks,Y.Fan

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#2 cn register 5

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Posted 16 March 2013 - 03:27 PM

I use tube rings with my Oynx, or use its dovetail and accept that it's a bit out of balance.

That thing is the dovetail adaptor for the scope, you can fit tube rings using the outer holes or use the centre hole to mount a camera.

Chris

#3 Raginar

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Posted 16 March 2013 - 03:34 PM

You need a longer dovetail. They come in whatever lengths you need. Another option would be to add weight to the from end.

My setup is just like Chris's, I have rings.

#4 cruling

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Posted 16 March 2013 - 04:13 PM

Thank you Chris, I will go find some tube rings.
i see orion has one with 90mm diameter and i think it will fit, may i ask what kinda dovetail you put on it? I mean the spacing between the two mounting ring seems to be limited by the dovetail bar. orion has one universal dovetail bar, but it says "narrow", i don't know if it will fit the CG5 saddle

#5 cn register 5

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Posted 17 March 2013 - 04:57 AM

The CG5 saddle is the small Vixen compatible size, I guess that's what Orion mean by "narrow" but asking them would be a good idea.

You may need to drill holes in the dovetail to get the right spacing for the tube rings.

Chris

#6 Raginar

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Posted 17 March 2013 - 03:36 PM

Cruling,

I just did a search and it looks like 90mm rings will work with your particular scope. Assuming the CG-5 has a vixen saddle, you just need to get one that fits the rings you buy. http://www.optcorp.c...tail-rings.html

You could get those with a longer bar so it gave you the option to move the rings on the vixen dovetail?

http://admaccessorie...s_Dovetails.htm

Just get a long one. :)

And one last piece of advice, I've heard the ADM rings are the best. I have them, and I don't get flexure which can matter if you're guiding with two separate scopes. I've heard of people having issues with other brands.


#7 Whichwayisnorth

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Posted 17 March 2013 - 04:16 PM

If you do not require that the rings be adjustable, which can mar the finish, I recommend these: click here

Also as far as a dovetail goes, consider these: click here. although that may not be long enough for you. This is the set up I use.

#8 RTLR 12

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Posted 17 March 2013 - 04:20 PM

A Celestron Onyx will NOT fit 90mm rings. I have the ADM 125mm rings that is the size recommended to fit the Onyx.

Stan

#9 WarrenS

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Posted 17 March 2013 - 04:31 PM

A Celestron Onyx will NOT fit 90mm rings. I have the ADM 125mm rings that is the size recommended to fit the Onyx.

Stan


I second what Stan said. I started out with 100mm ADM rings on my Onyx and they barely worked. I switched to the 125mm's and have had no problems. ADM makes great stuff by the way.

#10 cn register 5

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Posted 17 March 2013 - 05:11 PM

I am using 90mm tube rings on my Oynx, the same size as the ST80 uses. These are tube rings, NOT guide scope rings. The rings come in two halves that clamp round the OTA, they don't have screws, or any means of adjustment.

If you want guide rings - with adjustment screws - then you will need bigger rings but for just attaching a scope to a mount there's no need.

Chris

#11 cruling

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Posted 17 March 2013 - 06:52 PM

Thank you all for the advice.

I measured the diameter of Onyx 80EDF, it's 90mm for sure, so I just ordered the 90mm tube rings, not the guide rings in which case you will need bigger diameter.

for the dovetail bar, i ordered the one from Astro Tech, I did a little bit calculation, and the 7" one will give me balance in RA axis, but hope it's strong enough.
the ADM one looks it's made from one solid piece of aluminium, feels very strong. I'll see how it works when I got the AT one.

again, thank you all for the kindly help.

#12 Raginar

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Posted 17 March 2013 - 06:54 PM

Cruling, yea, that was my bad. I posted the wrong link. I meant tube rings. Glad it's gonna work out :).

Good luck!






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