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Balancing 8 inch Edge SCT in R.A.

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6 replies to this topic

#1 Frank P

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Posted 10 December 2018 - 03:40 PM

Tried doing first light on my new SCT.  Mounted atop an Atlas GEM.  Cannot get tube to balance in DEC even sliding the Losmandy style plate to the extreme forward position.  Looking for ideas on how to solve this issue with a clean robust solution since Imaging is my main intended application for this new scope.  Any ideas much appreciated! Please note my title is incorrect - its not RA sorry.

 

Frank P


Edited by Frank P, 10 December 2018 - 03:51 PM.


#2 Jim Davis

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Posted 10 December 2018 - 03:51 PM

You could add a dovetail counterweight to the front: https://www.admacces...3-threaded-rod/



#3 photoracer18

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Posted 10 December 2018 - 03:52 PM

You need to put weight on the front of the OTA or plate. It can be either real weights or like moving your guide-scope closer to the front of the OTA or any other mounted item. Refractors often have the opposite balance problem in RA so I often add an extra ring at the back to carry weight.

 

Celestron still makes tube weights that replace a screw in the front of the tube and allow stacking more than one weight.


Edited by photoracer18, 10 December 2018 - 03:54 PM.


#4 Eddgie

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Posted 10 December 2018 - 09:51 PM

Or, you could just ignore it.   A small amount of imbalance is totally harmless 

 

People obsess about balance on GEMs and it simply is not necessary to have perfect balance.

 

Also, if the finder is off center, the asymmetric load will only have one perfect balance orientation.

 

There really is not a compelling need to have the scope in perfect balance though so my advice is just to get it as close as the dovetail allows and ignore it if you are not perfect (though that does not mean 15 lbs of inbalance is OK.  But a couple of pounds is no big deal). 



#5 Exnihilo

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Posted 11 December 2018 - 08:57 AM

Getting a dew shield may help as well, plus delay dew formation and protect from dust a little.

#6 RAKing

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Posted 11 December 2018 - 10:04 AM

Or, you could just ignore it.   A small amount of imbalance is totally harmless 

Actually, a small amount of imbalance is preferred - especially if you are imaging.

 

Most of us using GEMs have learned to keep our scopes off-balance in order to keep the gears properly engaged.  And the predominant way for the imbalance is to use the "East Heavy" method.  By that, I mean that if you let the rig go, it will slowly drop toward the east side of your mount.  We do this so the gears engage properly and the worm gear will "pull" the spur gear to the west.

 

To adjust the RA axis, I raise the counterweights about an inch when I am looking to the west and I lower them an inch or so when I am pointed to the east.  For the DEC axis, I prefer 'back heavy' and your SCT should be back heavy with the mirror and imaging gear on the back.

 

All mounts have a small amount of gear play and if your scope is perfectly balanced, it can "bounce" back and forth between the gear faces.  It's annoying as heck for a visual observer and disastrous for an imager.

 

Cheers,

 

Ron



#7 Cfreerksen

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Posted 11 December 2018 - 08:53 PM

If you have the D mount rail there is a threaded 1/4 20 hole in the front of the rail. You could just bolt a weight to the rail. The ADM accessory listed above will work best.




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