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Balancing iOptron GEM28

Mount Imaging Equipment Astrophotography
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#1 Krish27

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Posted 16 October 2021 - 11:40 AM

Hi All,

 

I bought iOptron gem28 yesterday for my Redcat51. I have 2 questions on its balancing & initial position.

 

1) With AVX mount, once mount is balanced, moving it to any angle on RA/Dec axis, it stays there (like in the photo attached). That way we know its balanced.
But in this case of Gem28 its always coming to front/initial position (like in photo attached). I am not able to figure out on how to confirm if the mount is balanced on RA, DEC respectively? Can someone please help with images on how it should look like once balanced and any additional details to get there?

 

2) Again in AVX there are clear lines for RA, DEC indicating initial position to start mount/polar alignment. I don't see such indicators on Gem28? Is something like that on this mount?

 

Thanks,

 

 

20211016_083218.jpg

 

20211016_090217.jpg


Edited by Krish27, 16 October 2021 - 11:41 AM.


#2 zakry3323

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Posted 16 October 2021 - 11:58 AM

Balancing the CEM28 properly is covered under Step 8 in your manual. It does not require visible indicators for proper balance or alignment. 



#3 Krish27

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Posted 16 October 2021 - 12:05 PM

Thank you. I gone through manual multiple times. But it was very confusing atleast for me. May be because i am used AVX and this works differently. Hence the request here.



#4 Tom M

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Posted 16 October 2021 - 01:03 PM

I balance my GEM28 in 3 basic steps - but it's an iterative process.

 

Do a rough initial balance with the RA & DEC axis so they won't strain anything if the locks are used.

 

  1. Place the DEC axis horizontal and ensure that the RA axis is balanced - adjust CW as needed to get RA balanced then lock RA in place - use the hex key or clutch lock depending on your comfort level.
  2. Rotate scope in DEC so it's level and slide back/forth in the saddle to get if balanced fore/aft.
  3. Rotate the scope to vertical and see if it falls off to one side - if so either rotate the entire scope in the rings to eliminate the motion or add an additional weight (as in the photo) to the dovetail/saddle to complete the 3D balancing.

Repeat steps 1-3 again as necessary to verify the final balance. If the 3D balance was achieved by rotating the scope then you should, in theory, be done. If you added a 3D CW then you'll need to repeat the process at least once. The side benefit of the 3D weight on the dovetail is that the fore/aft balance can also be adjusted by sliding the the assembly along the dovetail. I use dovetail adapters that I get from ADM but I 3D print my own counterweight shells and use 3/4" washers, but any filler will work.

Attached Thumbnails

  • VPA-EAF-1.jpg

Edited by Tom M, 16 October 2021 - 01:05 PM.


#5 brentknight

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Posted 17 October 2021 - 08:00 PM

Tom,

You replaced the stock saddle to add that extra CW? Can something like this be done with the stock saddle and a standard Vixen dovetail?

No amount of rotation in the tube rings gets me to balance. No-friction bearings are nice, but tough to balance...

Edited by brentknight, 17 October 2021 - 08:01 PM.


#6 Tom M

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Posted 17 October 2021 - 09:13 PM

Tom,

You replaced the stock saddle to add that extra CW? Can something like this be done with the stock saddle and a standard Vixen dovetail?

No amount of rotation in the tube rings gets me to balance. No-friction bearings are nice, but tough to balance...

Sorry if I wasn't clear. I replaced the stock saddle in order to get more surface contact on the dovetail. Adding the 3D CW is totally separate from that and can certainly be done while using the standard saddle. The 3D CW slides along the dovetail so either saddle would allow for it.

 

Of note though is that adding the ADM saddle adds enough weight to the one side that if you can't rotate the tube assembly to balance you will need an additional weight to do the 3D balance as even with nothing mounted the DEC axis will want to rotate due to the weight of the knobs.



#7 brentknight

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Posted 17 October 2021 - 09:30 PM

I've got an ASiair Plus coming (hopefully) in November and that's going to determine my ultimate balance.  I can't tell from your picture what you have on the mount, but it looks like you used 7lbs of weight?

 

I've got my AT72EDII on risers, and I can get almost 360° rotation, but I can't get the balance correct in every position.  I'm going to hold out until the AA+ arrives (looks like the counterweights are backordered everywhere anyway), but I appreciate your shared experience.



#8 Tom M

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Posted 17 October 2021 - 10:17 PM

That's an FLT-91 and the 3D weight is roughly 200 grams.




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