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A Basic Refractor/Mount Q

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#1 Joe1950

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Posted 07 November 2019 - 12:43 PM

[Maybe better in ‘Mounts?’]

 

 

I have two refractors: A very nice C80ED f/7.5, and a Celestron Omni XLT 102 ED (which is actually a 100mm, f/9). They are good scopes for me, both bought used. Both have upgraded dual speed focusers.

 

Here is the 100mm...

 

5DFBCD11-B919-4DD1-8084-CFE586FCDE11.jpeg

 

Right now, the only mount I have is the Vixen Porta II, sitting on a common aluminum channel tripod. The 80mm rides it nicely. The 100mm has some annoying moment arm sway making focusing difficult.

 

Eventually I may build a pipe mount, but that is on hold for right now. In any event I don’t want something too heavy to carry outside.

 

Also, when out, I have to move among the trees.

 

So my question is... Has anyone used the hanging chain method to successfully lessen moment arm sway?

 

I’ve read about it but just looking for some feedback.

 

Im not going to wrap the chain around the tube, so I guess some kind of soft attachment might work. If I recall the chain attaches near the front of the scope?

 

As far as the chain. Do you use the heavy gauge chain? Or is medium okay? And about how long would be good? I was thinking 3 ft? At the home store, they have to cut the stuff and I don’t want to come home with too much.

 

 

Any info or experience is welcomed. Not an ideal solution, but likely the least expensive, which is numero uno at this time.

 

Thank you! 

 

 

 

 



#2 Jeff B

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Posted 07 November 2019 - 01:04 PM

Which axis is your moment arm sway?


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#3 vtornado

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Posted 07 November 2019 - 01:10 PM

Hi Joe Do you have a link to the hanging chain thread?

I assume??? this is a chain acting as a weight hanging from the underside of the mount head.

 

I have the same issue with my orion 100mm f9 ED.  Hard to focus on the porta mount,

so I am vested in your problem as well.

 

Wooden legs will probably get rid of some shake.  Could these be home made?

They are also available on craig's list by buying a old unloved scope with wooden legs.

There are two sizes of vintage legs if you go this route, get the bigger ones.

 

You could make homemade VSPs for a few dollars.  However I have found they REALLY

help when the tripod is on a hard surface.  Your setup in the woods might not be as big of a help.

 

Another thing I have heard of doing is using a doggie auger and a bungee cord to pull the

mount down. 

 

Can you remove the dew shade?  And how heavy is it?  Compare it to the weight of a flex dew shield.

That is taking weight off the end of the scope, if there is a difference in  weight.

 

To help you analyze the problem you could take a movie of your scope after you touch the focuser to

see where the vibration is coming from.  Play it back in slow mo.  Are the legs twisting, mount head shimmying?

I have a problem in the joint of the alt axis.  flicking my scope I can see the joint open an close.

I tightened the joint by popping off the cover, however you if you over tighten the mount is too stiff to use.

There is a butter zone.

 

I bought a 102 f/10 GT to test. It is much lighter (7 lbs), still has a problem.

 

===========

 

An out of the box idea is to get a celestron HD alt-az mount.  I have not tried this, but this mount head

is unique in that it holds the scope directly underneath instead of off to the side.  I have a head and legs, but

have not tried it yet.  The 100ED may be too much scope for the mount.  This head does have a problem with

tipping up as it approached zenith.  The reason why I mention it is this mount head can be purchased

used here for $20.00.


Edited by vtornado, 07 November 2019 - 01:17 PM.


#4 wrvond

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Posted 07 November 2019 - 01:16 PM

I’ve used it on a Dob, never heard of it on a frac. hmm.gif


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#5 BFaucett

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Posted 07 November 2019 - 02:14 PM

I’ve used it on a Dob, never heard of it on a frac. hmm.gif

 

Tune Up Your Telescope
By: Michael Portuesi | July 31, 2008

Sky & Telescope

https://www.skyandte...your-telescope/

 

Tune-Up-telescope-with-chain.jpg

 

 

The article only has a few sentences about it.  I've never tried it. 

 

Cheers!  Bob F. smile.gif


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#6 Joe1950

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Posted 07 November 2019 - 02:19 PM

Jeff, the motion is in the horizontal plane. 

 

 

Vtornado, I’m not familiar with the thread you mention. I know there was an S&T article about it, but what issue, have no idea. They hung the chain from the front of the tube, and somehow it acted to dampen the moment arm sway.

 

I’ve heard of the tie-down idea as well as the idea of hanging a gallon jug filled with sand or water from the center, under the mount head. I guess they all help, but I thought I’d start with the chain.

 

I’ll try the video thing to see what is flexing. Good idea. From past mounts, it seems the joints at the connection points of the tripod legs and the mount were always a weak point. But I’ll check it further.

 

 

Wrvond, I guess it can help with any vibration on different scopes. The S&T article used it on a fract. The weight of the fract tubes is not so much a problem as is the length.

 

The effect of moment arm sway increases with the distance (from the balance point) squared!  So the longer tubes are really affected. If the chain helps on the DOB, all the better!

 

 

Thanks all. Appreciate the replies!


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#7 Joe1950

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Posted 07 November 2019 - 02:23 PM

Ah!  That’s it, Bob! 

 

A picture is worth a thousand words!  I’ll give it a try. Looks like a heavy duty chain, couple feet doubled over.  I’ll know what to get at the home store!

 

Thanks Bob. Good find/memory!

 

 

 

.... there is the gallon jug fix too. I’ll start with the chain first. Seems easy and not too much more weight!


Edited by Joe1950, 07 November 2019 - 02:29 PM.

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#8 BFaucett

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Posted 07 November 2019 - 02:29 PM

You're welcome!  I just used my Google-foo to find it.  grin.gif  In the photo, it also looks like they used a rope or cord to tie the chain to the scope. That would seem to help with not scratching the tube but, like I said, I've never tried this. 

 

One other reference I ran across:

 

"Attach a chain to the telescope tube. Get a three-foot length of metal chain, with one-inch links, from the hardware or home improvement store. Drape the chain over one end of the telescope tube, and fasten with some duct tape. As the scope jiggles, each link in the chain will absorb a little bit of the vibration and quickly dampen the telescope tube."

http://www.sfsidewal...store-telescope

 

I'm glad I could be of some assistance.

 

Cheers!  Bob F. smile.gif


Edited by BFaucett, 07 November 2019 - 02:34 PM.

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#9 clearwaterdave

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Posted 07 November 2019 - 02:30 PM

Joe.,I hope I am wrong and that you prove me to be so.,but I'm afraid you can wear yourself out trying to make this set up work.,The scope is just to long for the mount/tripod for higher power use.,

  Please prove me wrong.,lol.,


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#10 Joe1950

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Posted 07 November 2019 - 02:48 PM

Thanks again, Bob!  It’s certainly worth a try for what’s involved.

 

Dave!  I had to put the pipe mount on hold for a couple months.  So I’m gonna give this a try to see if it helps in the mean time. Nothing beats those pipe mounts!  I’m not gone crazy trying all kinds of bandaids. Just the chain.  Plus when I saw the article a while back, I became curious about it!  I’ll defiantly report on the ‘before and after’ with photos.


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#11 Eddgie

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Posted 07 November 2019 - 04:47 PM

I don't think chains are all that effective.

 

My suggestion is to use vibration suppression pads. These actually work.

 

https://www.amazon.c...135060952&psc=1

 

Also, try to eliminate any play from the tripod.  Check the top bolts of the legs to ensure that they are tight, and make sure that the leg clamps are tight on the center post. 

 

You may want to inspect your center post too.  Make sure that it is in full contact with the out legs.  If there is any wiggle between the center leg and the outer legs, try to eliminate it.

 

Tightening up the mount and using VSPs can improve things, but a heftier mount is indeed the right direction to go. 

 

If the mount came with a tray that mounts on to the spreader, make sure you use it.  If not, consider cutting a disk of wood that you can use as a spreader. Just mark a hole where the disk sits on top of each beam on the splitter, drill a hole, and put 1/4-20 bolts and wing nuts in there.  When you are ready to observe, bolt this in.  You can even drill some holes in it for eyepieces. 


Edited by Eddgie, 07 November 2019 - 05:20 PM.

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#12 Eddgie

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Posted 07 November 2019 - 05:19 PM

And I posted a while back on the problems with one of the problems with these aluminum leg tripods, and that is that if you have the top bolts really tight to eliminate all flex at this point, the legs will be too stiff to fold easily. and most of these don't have hand knobs on the leg attachment bolt, so you need a tool.

 

Here was my fix for that:

 

post-14923-0-19222400-1570150988_thumb.jpg

 

The biggest problem with these tripods is that when the tripod is extended, the center tube of the tripod legs has a lot of flex.  This is why you see people using a semi-pier a lot.  This allows you to lower the tripod legs into a stiffer configuration.  It is really the tripod that is the weak point in most mounts. 

 

 


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#13 Joe1950

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Posted 07 November 2019 - 07:10 PM

Good points, Ed.  I have the bolts so tight I can’t fold the legs in.  Makes it hard getting out the door.

 

The center shelf is useless as there is play in the hinges and the arms. I think a solid wood kind that can be tightened with a knob bolt would be much better.

 

I think a stout tripod would make a lot of difference. The mount itself isn’t the best, but it doesn’t seem to be flimsy either. 

 

Thanks for the link. That’s a good price for those pads. I’ve never tried them though.

 

I think the tripod has a lot to do with it. If I can beef it up or find a good used job, I’d probably be better off all around. Maybe I’ll look around first. Planets are gone, so no big rush.

 

 

Thanks Ed!




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