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CEM25 Loading Instructions

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#1 ravi.krkl

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Posted 12 October 2019 - 12:59 PM

I got a IOptron CEM25 mount and Orion F3.9 Astrograph. I am new to big telescopes and I need some help in mount balancing instructions. In the attached picture, combined weight of OTA/Imaging Camera/Guide scope+Camera is 12Kg's. As per the CEM25 manual "Payload of 27 lbs (12.3 kg) with the mount-only weight of 10.4 lbs (4.7 kg)". Mount came with 4.5Kg counterweight. Do I need to buy additional 2 of them so that I can properly balance it?  Theoretically I feel yes. Hope it wont be a too much load on the mount.



#2 mistateo

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Posted 12 October 2019 - 01:25 PM

I hate to be "that guy" but you are likely going to struggle with that combo.  You are right at the weight limit, plus an 8 inch newtonian will catch the breeze very easily on a small mount like this.  At nearly 800mm focal length, many of the cameras will give you an imaging scale that will be tough to deal with using this combo.


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#3 OldManSky

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Posted 12 October 2019 - 02:22 PM

There was no attached picture...

What size mirror is your f/3.9 Orion astrograph?  If it's the 8" (200mm mirror), you're pushing the limits of the CEM25.  I successfully image with a 6" (150mm) f/4 Newtonian, with total weight of the scope/rings/camera/guider/etc. being at about 17 pounds, and that's about as high as I would go.  The issue is partly the weight, and partly the sheer size (mostly length) of an 8" scope.  It's a sail in the wind, it has a large moment arm, and much of the weight (around the focuser/camera) is far from the center of balance.

 

It's certainly worth a shot, you won't hurt the mount or anything.  You *will* need additional counterweights, probably 2 more.  Try to get the counterweights as close to the top of the counterweight shaft as possible.  Balance is critical to good operation of the CEM25, and a Newt with the camera hanging way off the central axis can be challenging...but doable.

 

 

Attached Thumbnails

  • setupforimaging.jpg


#4 ksouers

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Posted 12 October 2019 - 05:29 PM

I have to agree with the others, 12kg is really pushing it with this little mount.

Balance is critical with this mount, moment is it's enemy. The motors are small, not very powerful, so the mount is very sensitive to balance and moment.

 

My imaging rig is about 15-16 pounds, but most of it is far from the center of rotation causing moment issues. I've since moved my imaging to a CEM60EC.

 

You might try rotating the OTA so that the focuser is underneath if possible, unlike in Paul's picture where it is on top. This will put the mass of the imaging train a little closer to the center of rotation and might allow you to move the weights a little higher towards center. Both will help mitigate moment issues.

 

The CEM25 is a nice mount for small scopes. Just beware it does have limitations.

 

 

Kevin



#5 OldManSky

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Posted 12 October 2019 - 10:24 PM

Hey Kevin, just FYI...at least with the 6" I have, I can't put the focuser on the bottom.  When balanced, the focuser is too close to the front of the DEC head to do that, the focuser hits the front of the mount :(



#6 ravi.krkl

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Posted 13 October 2019 - 07:21 AM

My bad. I did not notice that image size was above 500KB hence it wasn't attached. OTA is Orion 8" f/3.9 Newtonian Astrograph.

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  • 20191012_223658-1.jpg

Edited by ravi.krkl, 13 October 2019 - 07:22 AM.


#7 ksouers

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Posted 13 October 2019 - 11:08 AM

Hey Kevin, just FYI...at least with the 6" I have, I can't put the focuser on the bottom.  When balanced, the focuser is too close to the front of the DEC head to do that, the focuser hits the front of the mount frown.gif

Hi Paul,

I didn't mean to criticize your method. I'm sorry it appeared that way. I merely wanted to point out to the OP that it was possible to put the focuser under the OTA, if he had the space.

Quite evident from the photo you couldn't do it any other way.

 

 

Kevin


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#8 OldManSky

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Posted 13 October 2019 - 11:23 AM

Hi Paul,

I didn't mean to criticize your method. I'm sorry it appeared that way. I merely wanted to point out to the OP that it was possible to put the focuser under the OTA, if he had the space.

Quite evident from the photo you couldn't do it any other way.

 

 

Kevin

Oh, hey, no worries -- I didn't take it as criticism!  Just wanted to point out to the OP that because of the CEM25 design (where the motors are, and the DEC axis being at the back of the RA instead of at the front like a traditional GEM), that's a lot harder to do.  I wish it were not that way, because you're right -- that does make balancing easier! smile.gif


Edited by OldManSky, 13 October 2019 - 11:24 AM.


#9 scadvice

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Posted 14 October 2019 - 07:34 PM

Wow...that is a big scope for the little CEM25 but if it can be done that is the mount to try on. Keep us up to date!


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