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Celestron C4.5/ Vixen Polaris Mount

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#1 Sk240

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Posted 13 February 2024 - 03:34 PM

I recently purchased a C4.5 reflector and Vixen Polaris mount for $50, the seller said it was originally purchased in the early 1990s.  The C4.5 has a Telrad, so I figured that between the Telrad and the mount, it'd easily be worth $50.  The tube has the older style tube rings and the OTA is crushed and dented all over.  I decided to collimate the C4.5 (it loses collimation on the primary mirror very easily, could be user error) and tested it with my C6 and Omni 102mm achromat (Costco special).  Surprisingly the C4.5 held its own.  Images are close in sharpness to the other two scopes but just a bit less bright.  Jupiter and the moon were really crisp, about as sharp as the C6 but just a bit dimmer.  I'd argue that for lunar and planets, the C4.5 is preferable over the Omni 102 due to lack of CA and longer FL (F7.9 vs F6.5).

 

The Vixen Polaris mount is an order of magnitude better than the alt-az mount that came with the Omni 102.  The Vixen mount was rock solid, even with observing off a 2nd story deck while the Omni 102 mount would shake pretty badly even under slight wind or focus adjustments.

 

Anyhow, because of the crushed tube, it was hard to rotate the C4.5 in eq mode so I decided to use the scope in alt az mode.  This worked pretty well, especially when a counterweight was added to balance out the mount/tripod.  I've read that in alt-az mode, the mount can support more weight, so I'm trying to decide whether splurging on the ADM vixen saddle conversion ($129) would be a worthwhile investment. 

 

For those who own a Vixen Polaris mount, what is the heaviest scope you've tried it on?  From what I read on here, it should handle my C6 well but I'm thinking of buying a 4", F6.8 triplet in the near future (12 lbs w/o diagonal and eyepieces), would this mount be able to handle the scope in alt-az?  Could it work in eq mode if I add more counterweight?

 

 

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Edited by Sk240, 13 February 2024 - 03:36 PM.

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#2 Sk240

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Posted 13 February 2024 - 03:35 PM

Picture of the crushed tube.

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#3 apfever

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Posted 13 February 2024 - 08:34 PM

The C6 newtonian and the C8 CAT were the heaviest that Celestron put on the Polaris. Both of those OTA were quickly moved up to the Super Polaris by Celestron when they determined the scopes were at the upper limit of the mount.  The basic C6 newtonian weighs 12.4 lb. with finder only, no eyepieces or other accessories. You are looking at around 13 pounds and it will take two threaded weights to balance, one large and one regular weight. 

 

Fixing the tube crush is easy by mounting the rings to the TOP of the saddle tangs using the accessory flats on the rings. Remove the inserts in the saddle tangs, and get a 1/4-20 clamp knob that wont go all the way through the tang and ring, and into the OTA.  Then insert a board into the bump outs that originally went around the saddle tangs. Tighten the original clamp knobs onto the board. This works so well you can easily rotate a tube already mutilated by the crush. 


Edited by apfever, 13 February 2024 - 08:37 PM.

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#4 Sk240

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Posted 14 February 2024 - 02:31 AM

Thanks for the tip on fixing the tube crush, I'll look into that!

Based on the info you provided on the C6 newt and C8 being moved to the Super Polaris, I'm guessing that a 4" triplet is likely too much scope for the polaris mount to handle.

#5 apfever

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Posted 14 February 2024 - 05:33 AM

It isn't just weight, it is also length. The longer a tube, the more moment arm it has and the more it will be able to shake. A very fast triplet would help but

Yeah, a 4" triplet sounds pretty darn heavy. 


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#6 Sk240

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Posted 14 February 2024 - 12:34 PM

 I found your writeup on how to do this, thank you!

 

https://www.cloudyni...ing-mount-easy/



#7 apfever

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Posted 14 February 2024 - 01:55 PM

What I did not show is the OTA taken off the mount.  No more loose rings slopping around the OTA, they stay where they need to be to bolt back up next time. I suggest NOT putting a radius on the stick to match the OTA. Leave the stick flat so the sides ride up a little off the OTA. This lets irregularities rotate through the stick quite nicely, either direction.  There is still plenty of contact surface down the length of the stick. 

 

I do a lot of things like this once and move on. In this case I did both C4.5 and the C80 (on ground in box). 

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Edited by apfever, 14 February 2024 - 01:56 PM.

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#8 Sk240

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Posted 14 February 2024 - 08:13 PM

That's a good tip, I was just thinking of 3d printing the stick and adding a matching radius. You just saved me some additional design error. Thanks! Thanks for the pics too.

#9 Brent Campbell

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Posted 15 February 2024 - 04:01 PM

Boy that orange C80 sure looks sweet.   I've owned a polaris, in my opionion it was built better than the super polaris.   

The polaris has a weird way of attaching the tube, with screws that put pressure on the rings which then snugged thescope onto the mount.   They had a reputation for being "tube crushers". ADM makes a dovetail conversion kit for the polaris that will give you the ability to use standard vixen dovetails - inmy opionion it would be a great upgrade.

 

Now about the tube.  I straightend my 10" dob tube that got bent in shipping by making two circular plugs and putting my truck sizzor jack between them.   Since your tube is for a 4.5" you might be able to take it down to a muffler shop and use a tube expander to push the dent out.  

 

 

Here are a couple of options on Amazon:

 

https://www.amazon.c...1zcF9tdGY&psc=1

 

https://www.amazon.c...aps,371&sr=8-15


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#10 Sk240

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Posted 15 February 2024 - 11:44 PM

Thanks for the tip, yeah, I was thinking about the ADM saddle but it's not cheap ($129). It's more than what I paid for the mount and scope ($50) but at the same time, the mount and ADM saddle would come out to $179 and I don't think I can get a better mount for under $200.

#11 Brent Campbell

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Posted 19 February 2024 - 02:45 PM

Thanks for the tip, yeah, I was thinking about the ADM saddle but it's not cheap ($129). It's more than what I paid for the mount and scope ($50) but at the same time, the mount and ADM saddle would come out to $179 and I don't think I can get a better mount for under $200.

No you can't.


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#12 Jon Isaacs

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Posted 20 February 2024 - 03:41 AM

I believe most C4.5s suffer from damaged tubes.  The one I had certainly did.

 

I believe the tubes are the same diameter as most 4.5 inch Newtonians.  Replacing the rings with modern hinged rings allows the tube to be rotated more easily.  

 

Jon



#13 Astrojensen

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Posted 20 February 2024 - 04:51 AM

 

Replacing the rings with modern hinged rings allows the tube to be rotated more easily.

Yep. The OTA diameter is 140mm. Standard tube rings from Orion or Synta/Sky-Watcher fit. I used 140mm rings from TS to upgrade the Polaris mount on my Vixen RC-125M. 

 

gallery_55742_4772_550596.jpg

 

 

Clear skies!

Thomas, Denmark


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#14 Sk240

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Posted 21 February 2024 - 02:39 AM

That's awesome to hear. I just bought the ADM saddle yesterday and can't wait to try it with my C6 SCT. Getting the tube rings for the C4.5 makes sense so I don't have to take off the saddle when I want to put on the C4.5.


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#15 jkmccarthy

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Posted 21 February 2024 - 03:33 AM

Sorry but I've just discovered this thread.   My only dislike regarding ADM's Vixen Polaris adapter for ADM's V-style dovetail are the very-acute-angle corners, circled below:

 

ADM_Vixen-Polaris-Adapter_01.jpg

 

... which do indeed protrude out from the unit when installed in the Polaris mount's saddle:

 

ADM_Vixen-Polaris-Adapter_02.jpg

 

Just be careful around the OTA's attachment to the mount in the dark, not to accidentally bump hard into those protruding acute-angle corners, if these haven't yet been eliminated....

 

Clear Skies,

 

       -- Jim

 

 


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#16 Sk240

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Posted 23 February 2024 - 11:09 PM

Thanks for the tip! I have a dumb question, I got the ADM saddle but I think they might have forgotten to send the screws to secure the saddle to the mount. Or am I supposed to use the existing screws on the mount somehow to secure it?

#17 Sk240

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Posted 24 February 2024 - 01:08 AM

I ended up picking up two M8-1.25x14mm socket cap screws to attach the saddle to the mount.
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#18 Terra Nova

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Posted 28 February 2024 - 01:22 PM

I believe most C4.5s suffer from damaged tubes.  The one I had certainly did.

 

I believe the tubes are the same diameter as most 4.5 inch Newtonians.  Replacing the rings with modern hinged rings allows the tube to be rotated more easily.  

 

Jon

The two that I had, had no dents what so ever. This one (my favorite)has different (non crushing) rings.

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#19 Sk240

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Posted 28 February 2024 - 02:35 PM

Did these rings come with the C4.5 or were they purchased separately?  Great looking scope by the way!  I see that you have the CG-4 motor drive for use with the Polaris mount?  I also read that there is a teeth difference between the CG-4 and the Polaris (144 vs 130) such that a crystal needs to be replaced but I'm thinking that the teeth difference is minor enough that you can use the drive as is and it will be good enough visually.



#20 *skyguy*

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Posted 29 February 2024 - 09:51 AM

Did these rings come with the C4.5 or were they purchased separately?  Great looking scope by the way!  I see that you have the CG-4 motor drive for use with the Polaris mount?  I also read that there is a teeth difference between the CG-4 and the Polaris (144 vs 130) such that a crystal needs to be replaced but I'm thinking that the teeth difference is minor enough that you can use the drive as is and it will be good enough visually.

I have a Tasco #1606 RA drive on my Polaris mount. It does a good job tracking the stars. I can walk away from the scope for an extended time and when I return, objects are still in the telescope's FOV (C102 F/9.8).

 

I purchased the drive from Telescope Warehouse years ago as new-old stock. It's a very rare item and extremely difficult to find.

 

Nexstar_102_Vixen_Polaris_Mount.jpg


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#21 Terra Nova

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Posted 29 February 2024 - 10:00 AM

Did these rings come with the C4.5 or were they purchased separately?  Great looking scope by the way!  I see that you have the CG-4 motor drive for use with the Polaris mount?  I also read that there is a teeth difference between the CG-4 and the Polaris (144 vs 130) such that a crystal needs to be replaced but I'm thinking that the teeth difference is minor enough that you can use the drive as is and it will be good enough visually.

Thanks. Those rings came with the scope when I purchased it, but they are not original, (I wasn’t it’s first owner). Yes, I used a CG-4 RA drive (actually an Orion EQ-3) that I modified with a diode replacement to get the correct sidereal tracking rate. All of that has been gone for a number of years.


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#22 Sk240

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Posted 29 February 2024 - 12:41 PM

Did you have to modify the diode on the clock drive like Terra did?

I have a Tasco #1606 RA drive on my Polaris mount. It does a good job tracking the stars. I can walk away from the scope for an extended time and when I return, objects are still in the telescope's FOV (C102 F/9.8).

 

I purchased the drive from Telescope Warehouse years ago as new-old stock. It's a very rare item and extremely difficult to find.

 

attachicon.gif Nexstar_102_Vixen_Polaris_Mount.jpg



#23 Sk240

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Posted 29 February 2024 - 12:42 PM

Did you modify it because you want to to use it for astrophotography?  Or was the mod needed for visual as well?

 

Thanks. Those rings came with the scope when I purchased it, but they are not original, (I wasn’t it’s first owner). Yes, I used a CG-4 RA drive (actually an Orion EQ-3) that I modified with a diode replacement to get the correct sidereal tracking rate. All of that has been gone for a number of years.



#24 Terra Nova

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Posted 29 February 2024 - 04:22 PM

Mainly Visual and  a little video astronomy


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#25 deSitter

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Posted 01 March 2024 - 02:58 AM

Sorry but I've just discovered this thread.   My only dislike regarding ADM's Vixen Polaris adapter for ADM's V-style dovetail are the very-acute-angle corners, circled below:

 

attachicon.gif ADM_Vixen-Polaris-Adapter_01.jpg

 

... which do indeed protrude out from the unit when installed in the Polaris mount's saddle:

 

attachicon.gif ADM_Vixen-Polaris-Adapter_02.jpg

 

Just be careful around the OTA's attachment to the mount in the dark, not to accidentally bump hard into those protruding acute-angle corners, if these haven't yet been eliminated....

 

Clear Skies,

 

       -- Jim

That's not a feature, it's a bug. You could put your eye out with that thing, Ralphie!

 

-drl


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