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iOptron CEM40 vs GEM45

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16 replies to this topic

#1 RonaldNC

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Posted 12 November 2020 - 09:33 AM

I'm putting up a permanent observatory in my backyard, including a dome and pier.  Initially, I am planning on using my Meade LX85 mount with the Meade 80mm APO Triplet Refractor.  I've not been real impressed with the mount (but love the scope) and am thinking about using something different on the pier.

 

I've seen a lot of positive comments here about iOptron mounts and am strongly considering purchasing either the CEM40 or the GEM45.  The prices are only about $100 apart... so does anyone have an opinion about which to go with... or even, what's the difference (other than the center balanced vs. traditional balanced)?

 

I plan on using this exclusively on my pier, so I don't care about portability factors, ease of polar alignment, etc.  Also, I would like to eventually mount my Celestron 8" HD Edge on the mount... if that makes a difference.

 

Any help would be appreciated!

 

Ron



#2 MrRoberts

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Posted 12 November 2020 - 09:46 AM

Other than the primary balance spot I believe they are identical. On a pier this mount should perform very well indeed with your ota's.

I have their CEM mounts for some time now and really like them using my CEM25P's/EC's and now the 40 which generally holds my Esprit120 and on occasions my C-8/E. Mine sits on the now eliminated 2" tripod, which I added TPI's leg stabilizer and tray.

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#3 RonaldNC

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Posted 12 November 2020 - 12:11 PM

Other than the primary balance spot I believe they are identical. On a pier this mount should perform very well indeed with your ota's.

I have their CEM mounts for some time now and really like them using my CEM25P's/EC's and now the 40 which generally holds my Esprit120 and on occasions my C-8/E. Mine sits on the now eliminated 2" tripod, which I added TPI's leg stabilizer and tray.

Thanks for the feedback!

 

Do you use any software to control your mount, such as NINA, KStars, SGP, etc.?  If so, any issues?  I currently use KStars/EKOS.

 

Thanks!

Ron



#4 astrosatch

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Posted 12 November 2020 - 03:21 PM

I have Gem45 and find it very good. It replaced my heq5 pro belt modded mount which served me well for years. I have 8" quattro (10.5 kg with all equipment) and I think it is perfectly matched for it. Mount feels very well made and solid on literoc 1.75" tripod. Heq5 pro was not that stiff and solid on skywatcher tripod with same leg diameter. I use asiair pro and it works great. Cable management is great. I power asiair from dovetail saddle, so there is only one cable from mount to asiair. Very tidy.
I have better guiding from the box than heq5 pro belt modded and "dark frame optics" tuned.
Was researching and deciding between eq6-r and gem45 for months and I'm happy with my choice. Can't say much for cem40, but they both share the same important parts so I guess similar performance.

I live at 45deg latitude so gem45 is better suited for me and honestly I don't particularly like the appearance of cem40. But that is my personal taste.
It is light and small. One would think that a big scope is too much for it, but apparently not. It handles my bulky newton just fine.
I even asked Ioptron for reason why 7kg heavy mount carries same payload than eq6-r which is 10kg heavier. They poetically replied: "Our design principle is to enhance the bone, muscle, and heart while trim the fat."
That finally made my mind to go for gem45 and never look back.😆


I hope I helped you a bit with decision.

Have a great time with your future mount and clear skies.

Andrej

Edited by astrosatch, 12 November 2020 - 03:27 PM.


#5 RonaldNC

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Posted 12 November 2020 - 06:33 PM

Andrej,

 

Thanks for the info!  iOptron seems to have a great reputation.  I guess I'll just have to get my checkbook out!

 

Ron



#6 MikeCrapo

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Posted 12 November 2020 - 08:32 PM

I believe the 45 is a newer mount than the 40.



#7 astrosatch

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Posted 13 November 2020 - 08:10 AM

I believe the 45 is a newer mount than the 40.

Yes, and very little information about it. Not many users yet to get a clear picture of performance.

#8 honyi

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Posted 13 November 2020 - 12:57 PM

They appear nearly identical on paper. The main difference, from what i can see, is the latitude ranges which the two mounts can operate at. The GEM45 is definitely unsuitable for low latitude use (14 - 68 deg), while the CEM40 is unsuitable for high latitude use (0 - 60 deg).

 

Apart from this, given that the gears used are the same and the motors used are the same (heck, even the lower part of the mount is the same), I would presume that the performance of the cem40 can be safely extrapolated to the GEM45.



#9 RonaldNC

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Posted 13 November 2020 - 04:00 PM

Thanks!

 

The CEM seems to be a bit more flexible regarding latitude.  I don't see any performance differences, but the GEM45 will handle more weight... not an immediate concern for me.  However, I keep buying new imaging toys that are adding more weight!

 

I may need to take a look at the CEM70... lol!

 

Ron



#10 Beaverpond Astro

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Posted 14 November 2020 - 10:37 AM

Hi,

I've had my GEM45 for a few months now and am really liking it...

I have a GT102 (triplet) and a ZS71/GT81 piggybacked on it.

Also using an ASIAir to PA, plate solve, guide, image.

 

The guiding on the GEM has been quite good...I am getting .5" total rms on nights with decent seeing...sometimes long stretches around .4". 

I would assume that these results are similar to a CEM40.

 

cheers!

 

GEM45


#11 Beaverpond Astro

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Posted 14 November 2020 - 10:38 AM

p.s. the 'custom' counterweight solution in the photo has since been upgraded smile.gif


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#12 NoDarkSkies

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Posted 14 November 2020 - 12:15 PM

Also the GEM45 Payloads is 45 Pounds and the CEM40 Payload is 40 Pounds (Center Balanced Equatorial Mount)

So far I really like my CEM40EC (Center Balanced Equatorial Mount)

The GEM45EC Model (Low periodic error (<0.25 arc seconds rms) -v- GEM45 Low periodic error (< ± 7 arc seconds))

But also I really like the (Center Balanced Equatorial Mount)

For a permanent observatory I would go with the CEM60EC for Long Term.
But for now I am going with the Sky-Watcher EQ6-R Pro EQ Mount for my permanent observatory.50601376236_04dd6c9886_b.jpg

50601495052_a3639daf55_b.jpg


Edited by NoDarkSkies, 14 November 2020 - 12:43 PM.

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#13 Linwood

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Posted 14 November 2020 - 12:56 PM

p.s. the 'custom' counterweight solution in the photo has since been upgraded smile.gif

My first time out I had two handheld barbells wrapped in velcro.  The C Clamp actually looks like it would be more stable.

 

The "C" clamp stands for "Covid era parts shortgage substitution".  How they knew that a hundred years ago when it was named, I'm not sure. waytogo.gif


Edited by Linwood, 14 November 2020 - 02:46 PM.

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#14 RonaldNC

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Posted 14 November 2020 - 02:15 PM

It's like either one will do the trick... but now I'm leaning towards the CEM70 (since the CEM60 is discontinued).  Only problem is that nobody has any of these is stock!

 

Thanks for all the information!

 

Ron



#15 Michael Covington

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Posted 14 November 2020 - 02:25 PM

Internally, they are almost identical.  Owning a GEM45, I get the vague impression that the CEM40 might be slightly the better engineered of the two.  Under some circumstances (which you can easily guard against, once you know), the GEM45 head can go upside down, causing internal cables to unplug.  The CEM40's body design blocks that from happening.



#16 JohnMeggers

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Posted 27 November 2020 - 08:35 PM

I've read this thread with interest, and it seems like those who have used the CEM-type mounts think they work OK. I'm researching my next move in the mount department, and have looked at that alternative, but don't know much about how they work.



#17 Michael Covington

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Posted 27 November 2020 - 10:08 PM

One last detail.  The GEM45 is not a true GEM.  The counterweight shaft is not actually the same as the declination axis.  When you move in declination, the counterweight shaft does not rotate.  This is not a problem, but it shows that the design is not a traditional GEM.




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