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IOPTRON CEM120 EC2 GUIDE OR NOT GUIDE?

iOptron CEM120EC2 Equipment Equatorial Mount Guiding
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Riccardo Civati avatar
Riccardo Civati avatar
Good morning everyone

I recently purchased an ioptron cem 120 EC2.
I will soon take it to the observatory and put my 980 mm focal length apochromatic telescope on top.
I wanted to ask those who may already have this mount (EC or EC2 version) if they need autoguiding.
The exposures I intend to do reach a maximum of 10 minutes.

the weight of the tube including filters, camera and flattener is about 11 kg

CS
Riccardo
Stjepan Prugovečki avatar
Stjepan Prugovečki avatar
Hi ,
Not exact answer to your question , but maybe it could be useful to you
I have little brother of CEM120 : GEM 28EC that has na encoder only on RA .
My rig is APM/LZOS 100/800 , EFW and 571 camera, which is more than one meter long and is around 9kg in total.  This small mount handles 7min exposures (I did not try longer) at 800mm FL   without any traces of stars elongation. So I am not guiding at all , just using NINA direct guider to initiate dithering. 
Wery good polar alignment is needed though ( 1 minute or better).
From that, I am quite sure that for 10min exposures , you do not need any guiding
CS
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Riccardo Civati avatar
Riccardo Civati avatar
Stjepan Prugovečki:
Hi ,
Not exact answer to your question , but maybe it could be useful to you
I have little brother of CEM120 : GEM 28EC that has na encoder only on RA .
My rig is APM/LZOS 100/800 , EFW and 571 camera, which is more than one meter long and is around 9kg in total.  This small mount handles 7min exposures (I did not try longer) at 800mm FL   without any traces of stars elongation. So I am not guiding at all , just using NINA direct guider to initiate dithering. 
Wery good polar alignment is needed though ( 1 minute or better).
From that, I am quite sure that for 10min exposures , you do not need any guiding
CS

thanks

now i am very calm and happy
Piet Vanneste avatar
Piet Vanneste avatar
Hello Riccardo ,

I have two CEM120EC2's here in Belgium on a fixed pier.

One carries an Epsilon 130 with Pegasus EFW (deepsky) and Sharpstar 61 (solar) combo . 
I don't guide because of the short FL and FWHM and eccentricity is good.

The second carries a Lacerta 250 F4 with ZWO EFW , there I do guide .
There is a slight improvement in star parameters due to guiding.

Hope this helps

Piet Vanneste
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Stjepan Prugovečki avatar
Stjepan Prugovečki avatar
Riccardo Civati:
Stjepan Prugovečki:
Hi ,
Not exact answer to your question , but maybe it could be useful to you
I have little brother of CEM120 : GEM 28EC that has na encoder only on RA .
My rig is APM/LZOS 100/800 , EFW and 571 camera, which is more than one meter long and is around 9kg in total.  This small mount handles 7min exposures (I did not try longer) at 800mm FL   without any traces of stars elongation. So I am not guiding at all , just using NINA direct guider to initiate dithering. 
Wery good polar alignment is needed though ( 1 minute or better).
From that, I am quite sure that for 10min exposures , you do not need any guiding
CS

thanks

now i am very calm and happy

One thing to add is that in my case the balance plays very important role.  I have 2 additional counterweights on RA and Dec to enable very good "3D" balance. I always balance the best I can achieve (when mount is unlocked the complete rig stays wherever you push it ) . 
C S
Georg N. Nyman avatar
Georg N. Nyman avatar
I have the CEM120EC2 equipped with a12" TrussRC and a focal length of a bit less than 2 meters - and yes, I do guide for exposure times longer than about 120". Important for my setup was a correct polar alignment before I started at all. 120" subs are OK as long as I do not use my QHY600M camera - it is non-forgiving with its 61MPx. With that camera you can see that the stars are slightly oval, very little, but it does exist. Guiding with a time selection of 2,5 sec eliminates this and the stars are nicely round again. 
Another very important requirement with iOptron is proper and precise 3D balancing - if the entire system is a bit out of balance - forget it, you need permanent guiding every 60sec. 
This requirement of very precise balancing was one of the reasons why I went for a RCTruss - it is regarding weight distribution much easier to balance than a Newton with camera. 
Out of my experience and location (Bortle 3,5), I do not expose longer than 300 seconds - I do not see anything more or better at 600sec/subs after integrating the same overal time (like 1hr as example).
CS
Georg
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David Russell avatar
David Russell avatar
I have the standard CEM-120 without encoders. I have taken 900 second non guided test subs with my FSQ106 and they looked good except for over exposure.

however in general I do guide, and I feel its better to do so, even for 120 second exposures.

my image scale is now lower, because I am using a 10 inch RC at F5.9 which is about 1484mm focal length, and I shoot with a 2600MC.

I find longer guide subs to be better than short ones, and generally use 4.5 or 5.0 second guide exposures.

unsure if any of this relates to the EC version but thought I would share my experience.

Clear Skies.
AstroShed avatar
AstroShed avatar
I actually balance my Ioptron CEM70, which is the same as the 120, just a bit smaller, in 4 different axis, and it works extremely well, and makes a big difference to my guiding. My video about it here.

https://youtu.be/Gatkmt7BFew?si=PX74VrEFUG5tIFHQ
Stefano Pesci avatar
Stefano Pesci avatar
Ciao Riccardo, 
I have a CEM120EC (encoder in RA only) and mount a 10inch Newton F/4 with an ASI2600mm (about 0.70 arcsec/px). I guide at full focal length with a OAG and an ASI220, which gives a resolution of 0.80 arcsec/px on the guiding chip quite similar to the imaging chip. In nights of good or very good seeing I can manage an RMS of 0.25 - 0.50 arcsec/px, so subframes have generally very good stars. I keep guiding exposures in the 2" to 5" sec range.
Without guiding and a polar alignment 5'-10' error, I can manage about 60 sec without trailing.
This is a new setup that I'm testing.
Stefano
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Charles Hagen avatar
Charles Hagen avatar
I would recommend guiding, basically no matter the setup so long as you are using an OAG. With the appropriate PHD2 settings, guiding will not hurt, especially if using the guide algorithms that are most well suited to imaging with encoders such as Low pass. If your tracking is good enough on it's own, it simply wont make corrections and if it's not, the guiding will step in and save the exposure. It comes at a small enough cost that I see no reason not to
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Pete Bouras avatar
Pete Bouras avatar
To pile on to what Charles said, guiding can also minimize the effects of those pesky atmospheric waves and upsets that seem to happen all the time.
No perfect polar alignment or Tpoint model can help you with those, but guiding can save those subs.
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