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iOptron CEM vs GEM is one better for consistent imaging?

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#1 kdkleck1959

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Posted 03 October 2022 - 05:25 PM

I'm getting ready to move up from a Sky Guider Pro, looking for something that I can put more lens/refractor/camera weight on without getting bogged down in poor tracking and guiding.  One thread I was seeing on CN had a couple of recent GEM28 purchasers expressing frustration and looking for help; another person chimed in saying (paraphrasing here) that the recent GEM mounts from iOptron are poor performers but the CEM mounts are fine.

 

I'm looking to see if I can get some feedback here, trying to decide between the two types of mounts.  If anyone can speak from experience with iOptron products I'd be very interested.

 

I currently image with:

An iOptron Sky Guider Pro (which just croaked)

A Sky Watcher EQM35

Nikon DSLR's

W.O. Z61

Sky Watcher ED80

ZWO ASIAir

ZWO 120mm guide scope/mini cam

 

I'm looking to get a William Optics Redcat 71, maybe also image with a refractor in the 102 triplet range and of course also need to add in the ZWOAsi Air, guide scope/mini cam, DSLR and eventually a ZWO mono camera with filter wheel.  Any of these combined payloads would be too much for the EQM35.


Edited by kdkleck1959, 03 October 2022 - 06:03 PM.


#2 Schlansk

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Posted 03 October 2022 - 05:49 PM

I have GEM 45.  I cannot perform a comparison with CEM 40 but  I do not feel that guiding suffers due to the GEM vs CEM design. I would be curious to see a fair comparison.

 

My best case guiding is about .2 sec. error according to PHD2.  More commonly, Guiding is closer to .4 sec. error.  I do have annoying guiding problems, but I have no way of knowing whether PHD2 is set up perfectly, and whether CEM 40 would guide better.

 

My GEM 45 carries either my ES 127 refractor, or my Edge HD 8 SCT.  It is able to handle and guide these scopes accurately for imaging with no isssues.


Edited by Schlansk, 03 October 2022 - 05:53 PM.

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#3 Paul Muller

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Posted 04 October 2022 - 08:18 AM

I also have a GEM 45, which I have used with few issues. Any tracking problems I've experienced are likely caused by user error than fundamental issues with the mount. 

 

I don't approach the weight limit either - just a Stellarvue SV80 and Orion Starshoot autoguider and 50mm guide scope. 



#4 AstroSSM

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Posted 04 October 2022 - 10:01 AM

I haven't heard anyone state specific advantages or disadvantages of the GEM vs CEM design, but someone please correct me if there is such. The one nice thing the CEM design does is prevent the "upside-down" problem the GEM has if you release the locking and let the mount flip under its own weight. If it has enough momentum, it will pull past its stops and possibly unplug internal cabling, but this is very easy to avoid once you understand the procedures for setting it up and loading it. Not a big deal breaker if you ask me. As with anything iOptron, a few will get lemons, but most will get it good out of the box. Both the GEM or CEM will serve you well.

 

If you're looking for refractors in the 102mm range, the EQ6-R Pro would serve very well if you want to venture away from iOptron. It's a very well tried and true mount. It is a GEM design, but it's perhaps the best bang for your buck in its price range hands down. 


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#5 limeyx

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Posted 04 October 2022 - 01:09 PM

I'm getting ready to move up from a Sky Guider Pro, looking for something that I can put more lens/refractor/camera weight on without getting bogged down in poor tracking and guiding.  One thread I was seeing on CN had a couple of recent GEM28 purchasers expressing frustration and looking for help; another person chimed in saying (paraphrasing here) that the recent GEM mounts from iOptron are poor performers but the CEM mounts are fine.

 

I'm looking to see if I can get some feedback here, trying to decide between the two types of mounts.  If anyone can speak from experience with iOptron products I'd be very interested.

 

I currently image with:

An iOptron Sky Guider Pro (which just croaked)

A Sky Watcher EQM35

Nikon DSLR's

W.O. Z61

Sky Watcher ED80

ZWO ASIAir

ZWO 120mm guide scope/mini cam

 

I'm looking to get a William Optics Redcat 71, maybe also image with a refractor in the 102 triplet range and of course also need to add in the ZWOAsi Air, guide scope/mini cam, DSLR and eventually a ZWO mono camera with filter wheel.  Any of these combined payloads would be too much for the EQM35.

I am still "debugging" guiding on my CEM70. Maybe it's me. Maybe the mount somehow got damaged and I didn't realize it but kind of regretting this right now

 

However, the other options within similar payload/budget at the time I bought were not great - basically an EQ6R-PRO which has a lower payload and is less portable

 

I upgraded from the SGP as well and was hoping to get a "set & forget" mount that would just work.

 

The mount itself (except the mounting system for the pier) is intuitive, but I still get guiding spikes that I cannot get rid of and there is only so much mechanical work I feel comfortable with

 

I guess during next galaxy season I have to pay $200+ to send it back for someone who is supposed to know what they are doing to look at and hope it comes back in better shape



#6 Schlansk

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Posted 05 October 2022 - 09:56 PM

I also suffer from guiding spikes with my GEM 45.  I minimize the problem with better polar alignment and discarding frames (sometimes too many frames).  I can get pretty good imaging results at 1400 mm if I am careful.



#7 ScottS

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Posted 06 October 2022 - 07:33 AM

So, I'll put this out there: I just installed a new CEM120EC in my observatory, replacing my original CGE Pro. The CEM120EC is an amazing mount and it's probably the best and most accurate mount I've personally used, I've not used a GEM. Once I got the CEM120EC dialed in. I can tell you for certain, I really don't worry about what the mount is doing or not doing. After upgrading my mount, I'm now able to concentrate on all the other aspects of imaging. I think any higher end mount, mounts in the same class. Are going to make your imaging process more consistent and better, as far as what impact a mount has on the process. All mounts will have their users likes and dislikes. For me, I now have time to just get my routine down better, stop forgetting the simple things and make my process more like wash/rinse/repeat. I am do more things to improve myself as an imager and spend my time on the acquisition process. I'm not fighting or worrying about my mount keeping alignment, tracking etc.


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#8 EPinNC

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Posted 06 October 2022 - 09:48 AM

...maybe also image with a refractor in the 102 triplet range and of course also need to add in the ZWOAsi Air, guide scope/mini cam, DSLR and eventually a ZWO mono camera with filter wheel.  Any of these combined payloads would be too much for the EQM35.

If you're looking at a GEM28 (US$1500-1700), then you're probably comparing it with a CEM26 (US$1300-1500).

 

I have a CEM26, and I've considered getting something like an AT102ED, but I'm concerned about weight and tube length (angular moment).  With my DSLR attached, it might be a bit shaky for a GEM28/CEM26.  Yes, I'd still be below the 50% rule-of-thumb for rated capacity, but in the grand scheme of things, these two mounts are near the low end for imaging purposes and I would not expect a miracle.

 

Maybe I'm wrong, and a 102 refractor would work just fine.

 



#9 Bob_Gardner

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Posted 06 October 2022 - 11:29 AM

Recommend this CN thread for additional thoughts on this topic:

https://www.cloudyni...cem40-vs-gem45/



#10 Hans Joakim

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Posted 06 October 2022 - 12:02 PM

If you're looking at a GEM28 (US$1500-1700), then you're probably comparing it with a CEM26 (US$1300-1500).

 

I have a CEM26, and I've considered getting something like an AT102ED, but I'm concerned about weight and tube length (angular moment).  With my DSLR attached, it might be a bit shaky for a GEM28/CEM26.  Yes, I'd still be below the 50% rule-of-thumb for rated capacity, but in the grand scheme of things, these two mounts are near the low end for imaging purposes and I would not expect a miracle.

 

Maybe I'm wrong, and a 102 refractor would work just fine.

 

I have been using the TS102 F7 (https://www.teleskop...n-Objektiv.html) with the ASI294MC Pro and a 50 mm guidescope on the GEM28 with no problems. RMS guiding errors have been around 0.8. I have no experience with the CEM mounts, but assume the performance of the CEM26 would be practically the same as the GEM28. I also have the GEM45, which I’m very happy with. Very lightweight and portable considering its capacity, and some nice features that help with cable management. 


Edited by Hans Joakim, 06 October 2022 - 12:02 PM.

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#11 EPinNC

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Posted 06 October 2022 - 12:31 PM

I have been using the TS102 F7 (https://www.teleskop...n-Objektiv.html) with the ASI294MC Pro and a 50 mm guidescope on the GEM28 with no problems. RMS guiding errors have been around 0.8. I have no experience with the CEM mounts, but assume the performance of the CEM26 would be practically the same as the GEM28. I also have the GEM45, which I’m very happy with. Very lightweight and portable considering its capacity, and some nice features that help with cable management. 

Nice!  I now have hope that one day I'll be able to use that size of scope.  At f/7, that would give me a bit wider field than my Mak-Cass.


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#12 Kevin_A

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Posted 06 October 2022 - 07:14 PM

I have 2 iOptron Gem mounts and both suffer from occasional random spikes and also from guiding great then horrible. I think after trying everything under the sun to elliminate the issues the Gem’s suffer more from the main axis shaft bearing stiction to which does not seem as common with a Cem style mount. 



#13 Michael Covington

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Posted 06 October 2022 - 08:39 PM

I haven't heard anyone state specific advantages or disadvantages of the GEM vs CEM design, but someone please correct me if there is such. The one nice thing the CEM design does is prevent the "upside-down" problem the GEM has if you release the locking and let the mount flip under its own weight. If it has enough momentum, it will pull past its stops and possibly unplug internal cabling, but this is very easy to avoid once you understand the procedures for setting it up and loading it. Not a big deal breaker if you ask me. As with anything iOptron, a few will get lemons, but most will get it good out of the box. Both the GEM or CEM will serve you well.

 

 

You are exactly right about what I call "iUpsideDown."  I have a GEM45 and wish I had gotten a CEM40.  They are almost identical except for the body style.  I am not at all sure they really differ in load capacity.



#14 limeyx

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Posted 07 October 2022 - 01:30 PM

I have 2 iOptron Gem mounts and both suffer from occasional random spikes and also from guiding great then horrible. I think after trying everything under the sun to elliminate the issues the Gem’s suffer more from the main axis shaft bearing stiction to which does not seem as common with a Cem style mount. 

Sounds exactly like my CEM70 honestly. I'm going to capture a few worm cycles unguided on the next clear night to get a baseline. I did that before and don't remember anything bad. But still the random guiding persists



#15 kdkleck1959

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Posted 09 October 2022 - 09:50 PM

Thanks to all for your informative feedback and suggestions. I wasn't sure about the iOptron reliability issue and happened to luck across a Sky Watcher EQ6-R in excellent condition at the right price and jumped on it.  I swear it's as heavy as my Corolla but I tested it (no shots yet too cloudy) and the balance is so smooth and perfect, the mount so quiet when slewing...I can't wait to try some imaging.

 

Again thank you for sharing your thoughts regarding the iOptron mounts.  Now I can start obsessing on which ZWO mono camera to purchase...


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#16 Michael Covington

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Posted 10 October 2022 - 07:25 AM

The EQ-6R is one mount about which I never hear anything bad.  Congratulations on your purchase!


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#17 Mark Lovik

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Posted 10 October 2022 - 03:34 PM

The EQ-6R is one mount about which I never hear anything bad.  Congratulations on your purchase!

Except for the weight -- it can be a beast to handle at 38 pounds.  I wanted one but was dissuaded by friends with the mount.  I have an AzEq5 - much lighter and originally was very sensitive to wind.  Tuned up (which is fairly easy) this mount easily handles my 8" SCT or AT115EDT scopes for EAA and AP.

 

If I went to a higher capacity mount the iOptron models have an impressive capacity to mount weight ratio.


Edited by Mark Lovik, 10 October 2022 - 03:38 PM.

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#18 Bob_Gardner

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Posted 11 October 2022 - 04:15 PM

Except for the weight -- it can be a beast to handle at 38 pounds.  I wanted one but was dissuaded by friends with the mount.  I have an AzEq5 - much lighter and originally was very sensitive to wind.  Tuned up (which is fairly easy) this mount easily handles my 8" SCT or AT115EDT scopes for EAA and AP.

 

If I went to a higher capacity mount the iOptron models have an impressive capacity to mount weight ratio.

The weight of the EQ6R is what caused me to keep looking.  If all I had to do was take it out to the back yard, the EQ6R might have been ok.  But I have to drive 40 miles to get to a dark site without trees.  I've been using an Obsession 18UC for 12 years now and know how much time and effort is required to load, transport, set up, and tear down a scope/mount, even one that is designed to be light and portable, much less one that weighs 2-3 times as much.  I ended up getting a GEM45 in August which I am pleased with so far.  The ZWO AM5 and others of this sort are tempting, but I'm not interested in being a beta tester.  Decided to go with a slightly more mature product.  


Edited by Bob_Gardner, 11 October 2022 - 04:19 PM.


#19 zernikepolynomial

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Posted 13 October 2022 - 03:50 AM

Thanks to all for your informative feedback and suggestions. I wasn't sure about the iOptron reliability issue and happened to luck across a Sky Watcher EQ6-R in excellent condition at the right price and jumped on it.  I swear it's as heavy as my Corolla but I tested it (no shots yet too cloudy) and the balance is so smooth and perfect, the mount so quiet when slewing...I can't wait to try some imaging.

 

Again thank you for sharing your thoughts regarding the iOptron mounts.  Now I can start obsessing on which ZWO mono camera to purchase...

 

Smart move. iOptron gear is garbage quality right now. In the past, they seemed better, but in my experience, their products come with defects and they seem very hesitant to honor their warranty. 


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#20 rgsalinger

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Posted 14 October 2022 - 07:13 PM

The last two that I used, a CEM70 bought 6 months ago and an AZ Pro bought about a year ago were perfect out of the box. When we have member nights at our dark sky site, there are more of them than any other brand and I have yet to run across anyone with "spikes" out of the ordinary. How many have you owned or used?

 

In fact the 70 sat next to my MYT that night and guiding performance for both mounts with similar 4" refractors was pretty much the same all night.

 

Usually when you see spikes in a guiding run it has nothing to do with the mout per se. Dirt is a big factor along with wind and seeing. Since I'm able to use 2 systems about 100 nights a year, I've been amazed at how things can change during the course of the night. 

 

Rgrds-Ross


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#21 KTAZ

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Posted 14 October 2022 - 07:30 PM

Smart move. iOptron gear is garbage quality right now. In the past, they seemed better, but in my experience, their products come with defects and they seem very hesitant to honor their warranty. 

What were the defects and what did they refuse to take care of under warranty? Just curious as it is a data point some folks might like to hear about.

 

As with anything iOptron, a few will get lemons, but most will get it good out of the box. Both the GEM or CEM will serve you well.

 

If you're looking for refractors in the 102mm range, the EQ6-R Pro would serve very well if you want to venture away from iOptron. It's a very well tried and true mount. It is a GEM design, but it's perhaps the best bang for your buck in its price range hands down. 

Excellent points. My CEM70 arrived in less than perfect factory condition. It went straight onto the mount for a recording of the worm harmonics and failed my analysis. Back to iOptron and all repairs were handled with 100% professionalism and excellent communication. Upon return it hums like a kitten and provides excellent guiding and round stars.

 

I bought the CEM70 as an upgrade to my EQ6R Pro and it is definitely an upgrade. BTW, my EQ6R Pro also had to go back "out of the box" and was replaced rather than repaired. The second one ran very well, but not as good as the CEM70.



#22 KTAZ

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Posted 14 October 2022 - 07:40 PM

Usually when you see spikes in a guiding run it has nothing to do with the mout per se. Dirt is a big factor along with wind and seeing. Since I'm able to use 2 systems about 100 nights a year, I've been amazed at how things can change during the course of the night. 

 

Rgrds-Ross

Ross hits on a great point; the one potential weakness of the CEM70 design that I see is the partially exposed RA belt and worm spur. You need to take care in storage if you leave it outside where blowing dust and dirt might collect on the belt. Over time this could lead to the types of errors that Ross is eluding to. The belts in the EQ6R are completely covered.

 

I keep mine under a 360 cover with an additional drawstring bag to keep out the dust and spiders. I plan to open it up once every spring for a potential spring cleaning of that belt and gear.



#23 rgsalinger

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Posted 14 October 2022 - 09:56 PM

With all the mid priced mounts you're going to be dealing with quatlity control problems. Since they all come from China and get shipped here and there you're going to be dealing with shipping issues as well. These often end up in the hands of the inexperienced which adds to the overall confusion. Threads get started here and abandoned. I seriously doubt that there's a substantial quality difference between the Synta and iOptron mounts and that's been my experience as well. All of the synta and ioptron mounts I've owned (and those I've set up) have been fine out of the box. That's just luck though. 

 

Rgrds-Ross




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