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80mm Refractor - Replacing Dovetail Bar w/Rings

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#1 agkuz

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Posted 19 February 2019 - 11:38 AM

Hi All,

 

Just checking in to see if anyone has replaced the dovetail bar on their 80mm Apo Triplet with rings. I've found that the nuts holding it to the scope tend to loosen (haven't tried Loctite on them). I think I'd just prefer a more secure mounting method to my CGEM. I'm sure the single attachment point makes the scope (and the attached AP equipment) a little more susceptible to wind and vibration.

 

I must admit, though, that the one or two times my software has gone haywire and planted my scope firmly into one of my tripod legs (rookie mistakes-- facepalm), the loosy-goosy attachment point probably saved the scope from significant damage. I'm looking at the William Optics 90 mm Mounting Rings, and would mount them on a dovetail bar (since I already have an adapter plate for the CGEM), or a Losmandy D-style plate to possible get a wee-bit more stability onto the CGEM. I'm having a bit of a hard time figuring out if the 90mm rings would fit snuggly around the 80mm scope w/o extra padding.

 

Thoughts?

 

Thanks!!

 

Clear skies,

Alex


Edited by agkuz, 19 February 2019 - 11:39 AM.

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#2 Jeff Struve

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Posted 19 February 2019 - 11:46 AM

Can you get a clam shell set up?



#3 Jon Isaacs

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Posted 19 February 2019 - 11:58 AM

Alex:

 

Most 80mm apo refractors and achromats use 90mm tubes. I don't know about the Explore Scientific 80mm, give them a call, they should know.

 

Jon


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#4 agkuz

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Posted 19 February 2019 - 01:53 PM

Can you get a clam shell set up?

I think a clamshell would be great, if I could find one for an 80mm.



#5 agkuz

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Posted 19 February 2019 - 01:57 PM

Alex:

 

Most 80mm apo refractors and achromats use 90mm tubes. I don't know about the Explore Scientific 80mm, give them a call, they should know.

 

Jon

Will give it a shot, thanks!



#6 Simon B

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Posted 19 February 2019 - 07:26 PM

AFAIK it is 90mm, but don't take my word for it. If it IS in fact 90, and you don't mind buying via Aliexpress, here's a good quality ring set for half the price of the WO/Stellarvue rings:

 

https://www.aliexpre...2662121120.html

 

Okay I don't know that they are good quality rings, but they certainly look it. I often buy dovetails, adapters etc from this seller and never had any problems



#7 BFaucett

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Posted 19 February 2019 - 07:54 PM

I'm having a bit of a hard time figuring out if the 90mm rings would fit snuggly around the 80mm scope w/o extra padding.

 

Thoughts?

 

 

 

 

Just measure the circumference of the tube and then convert that to the diameter.

 

 

Calculator:

 

 https://www.omnicalc...h/circumference

 

To measure the circumference, I just use a strip of paper or a string wrapped around the tube.   I then measure the length obtained using a ruler.

 

Cheers!

 

Bob F. 



#8 agkuz

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Posted 19 February 2019 - 07:55 PM

AFAIK it is 90mm, but don't take my word for it. If it IS in fact 90, and you don't mind buying via Aliexpress, here's a good quality ring set for half the price of the WO/Stellarvue rings:

 

https://www.aliexpre...2662121120.html

 

Okay I don't know that they are good quality rings, but they certainly look it. I often buy dovetails, adapters etc from this seller and never had any problems

Thanks for the lead Simon! I'll check it out!

 

Best,

Alex



#9 agkuz

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Posted 19 February 2019 - 07:56 PM

Just measure the circumference of the tube and then convert that to the diameter.

 

 

Calculator:

 

 https://www.omnicalc...h/circumference

 

To measure the circumference, I just use a strip of paper or a string wrapped around the tube.   I then measure the length obtained using a ruler.

 

Cheers!

 

Bob F. 

Well I guess that would be pretty logical, wouldn't it? LOL. I'll grab a tape and see what it comes out to.

 

Best,

Alex


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#10 Agatha

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Posted 19 February 2019 - 08:10 PM

On the Explore Scientific website, both 80mm triplets are listed as 85 diameter.  As mentioned already, it would be good to contact them or measure it yourself.  

 

And if you choose to use a Losmandy type plate using two screws per ring, be sure to get the correct spacing for the threaded holes.  Universal plates are a bit more common now but it is worth checking.  Good luck.  



#11 agkuz

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Posted 19 February 2019 - 08:19 PM

The diameter is 91mm, so I *suppose* the 90mm rings would fit. But then I found another issue. Unless I remove the finderscope bracket, the rings are going to be about 4 inches apart at most. Seems a little silly (but maybe it could work?). If I could replace the finderscope bracket (which has my red dot finder and my guidescope) with another one without drilling (maybe mounted on a 3rd ring), we might be in business.

 

OR...if I could somehow rig it up so I use only one ring at the very front of the OTA and somehow get that bolted to the adapter plate forward of the where the existing dovetail bar ends, I would have my two mounting points. It's just that single mounting point that can't handle rotational stress that well if any significant amount of weight is applied to it.



#12 agkuz

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Posted 19 February 2019 - 08:22 PM

On the Explore Scientific website, both 80mm triplets are listed as 85 diameter.  As mentioned already, it would be good to contact them or measure it yourself.  

 

And if you choose to use a Losmandy type plate using two screws per ring, be sure to get the correct spacing for the threaded holes.  Universal plates are a bit more common now but it is worth checking.  Good luck.  

I did actually reach out to Explore Scientific. They sent me back a very unuseful reply: "I've seen photos of ED80s in rings. Certainly the correct size will work." As was pointed out to me just a bit earlier, it's certainly easy enough to measure my own diameter. The question is what the exact diameter of the rings are. It would just be nice to not have to line the rings with foam weatherstripping, though that may not be the worst thing if they're just a mm too big.


Edited by agkuz, 19 February 2019 - 08:25 PM.


#13 Simon B

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Posted 19 February 2019 - 08:30 PM

Another alternative, Vixen 90mm rings, $69.95:

 

https://www.vixenopt...90mm-p/2664.htm

 

 

The following thread might be the confirmation you're looking for:

 

https://www.cloudyni...let-m42-sample/


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#14 agkuz

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Posted 19 February 2019 - 08:37 PM

Another alternative, Vixen 90mm rings, $69.95:

 

https://www.vixenopt...90mm-p/2664.htm

 

 

The following thread might be the confirmation you're looking for:

 

https://www.cloudyni...let-m42-sample/

I think you hit the jackpot with that post! The rings he used were spaced pretty closely together, but I guess that's more than solid. Just can't drive the scope into the tripod legs anymore (wince). Plus they're only $35 on Agena w/excellent reviews: 

https://agenaastro.c...-90mm-3-54.html

 

You're awesome, thanks! Exactly the solution I needed but couldn't find.

 

EDIT:

I did notice on further examination that steven_usa removed the stock finderscope baseplate which allowed him to spread the rings out a couple inches further.


Edited by agkuz, 19 February 2019 - 08:54 PM.


#15 BFaucett

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Posted 19 February 2019 - 08:55 PM

The diameter is 91mm, so I *suppose* the 90mm rings would fit. But then I found another issue. Unless I remove the finderscope bracket, the rings are going to be about 4 inches apart at most. Seems a little silly (but maybe it could work?). If I could replace the finderscope bracket (which has my red dot finder and my guidescope) with another one without drilling (maybe mounted on a 3rd ring), we might be in business.

 

OR...if I could somehow rig it up so I use only one ring at the very front of the OTA and somehow get that bolted to the adapter plate forward of the where the existing dovetail bar ends, I would have my two mounting points. It's just that single mounting point that can't handle rotational stress that well if any significant amount of weight is applied to it.

 

 

Given slight +/- errors when measuring the circumference and then converting that to the diameter, I'd say 90mm is probably spot on. 

 

Distance apart:  Just as an example, here's the ring spacing on my Orion ST80.  I realize you have a different scope but maybe this photo will help you visualize a 4 inch spacing of the rings.  This works just fine on ST80.  

 

Just trying to be helpful.  Cheers!  Bob F.  smile.gif

 

 

gallery_230527_10757_2296709.jpg


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#16 Simon B

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Posted 19 February 2019 - 08:56 PM

No problem : )  good luck choosing rings! Lots in the 90mm size... William Optics ($$$), Stellarvue ($$$), Vixen ($$), Orion ($), GSO ($), to name a few : )


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#17 agkuz

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Posted 19 February 2019 - 08:59 PM

Given slight +/- errors when measuring the circumference and then converting that to the diameter, I'd say 90mm is probably spot on. 

 

Distance apart:  Just as an example, here's the ring spacing on my Orion ST80.  I realize you have a different scope but maybe this photo will help you visualize a 4 inch spacing of the rings.  This works just fine on ST80.  

 

Just trying to be helpful.  Cheers!  Bob F.  smile.gif

 

 

gallery_230527_10757_2296709.jpg

That's actually really helpful, Bob! Thank you! I just measured and I have about 5 inches max tip to tip. From what it sounds like it should work fine then!


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#18 BFaucett

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Posted 19 February 2019 - 09:01 PM

waytogo.gif smile.gif



#19 agkuz

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Posted 19 February 2019 - 09:08 PM

No problem : )  good luck choosing rings! Lots in the 90mm size... William Optics ($$$), Stellarvue ($$$), Vixen ($$), Orion ($), GSO ($), to name a few : )

I like the price of the GSO and Orion rings for sure ($35), though I like the flexibility to add on accessories on top later. But for the price (plus rail) vs. $120+ just for rings I think it might be worth the short-term sacrifice. And the Orion rings come with a piggybacking camera post (!!).



#20 jcj380

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Posted 20 February 2019 - 09:12 AM

No problem : )  good luck choosing rings! Lots in the 90mm size... William Optics ($$$), Stellarvue ($$$), Vixen ($$), Orion ($), GSO ($), to name a few : )

Orion says 90mm rings fit an ST80.


Edited by jcj380, 20 February 2019 - 09:13 AM.

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