Any feedback about CEM70 ? - Forums

Topic starter

Nov 16, 2020

Hi All,

Looking for feedback from new owners of a CEM70(G or not G).

Read some people had troubles using it with PHD2 while having PEC enabled… not sure if the problem comes from the user or from the mount, so I would love to get much more feedback.

I know lots of people loves the CEM60, but it won’t help as I am looking for the CEM70 : it is like with stock exchange… former performances are not a guaranty on how it will perform next 😬

Kind regards,

Lorenzo Siciliano

Nov 16, 2020

Hi Jérémie.
I do own a Cem70 not G. The vanilla one. I purchased it in late July.
It's a really beautiful mount. It carry with ease my 250 f/4 Newton ota even in moderate windy weather.
Tracking performance: very good. 180 sec unguided at 0.9 arcsec/pix. Total PE well within the factory specs (+/- 3" arcsec).
But it has an annoying backlash in dec. I'm still trying to address this issue.
I haven't tried PEC yet. I prefer going guided.
And I guide via Asiair, that uses a reduced version of PHD.
All in all is a good mount, stable and capable.
Definitely a step ahead with respect to my previous eq6.
Feel free to ask if you have any other question.
Ciao.
Lorenzo

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Jérémie

Topic starter

Nov 16, 2020

Thanks @Lorenzo Siciliano !
Wow, so without guiding, and no PEC, already good results...
I imagine that with guiding everything works well (well, your pictures speak both for you and the mount : splendid results !)
The Dec backlash : I imagine this is problematic for guiding, when the motor receive orders of correction in directions that changes ? I thought this could be setup in the guiding software ? Maybe not with the version of phd of Asiair ?
Let us know if you find a solution for it : I understood you can tweak the belt system to adjust the contact of the gears (not expert...)
If I see other positive feedbacks, I think I will go for it !

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Lorenzo Siciliano

Nov 16, 2020

Hi Jérémie.
unfortunately there's no backlash compensation neither in the asiair nor in the firmware of the mount.
Anyway, for now I'm addressing the issue guiding in only one direction, north or south, depending by the drift.
I tried to tweak the meshing between the worm and the gear and I'm waiting to test it under the sky, but both sky and covid do not cooperate…
Ciao.
Lorenzo

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spiantino

Nov 16, 2020

Disappointing to hear about the dec backlash. That plagues my current mount (EQ5), though with good seeing I can still manage under 1" after belt modding.

Two questions: do you regret not getting the G version (with USB3 and wifi)? And I believe it has a home registration feature, so do you still have to be careful about homing it precisely before turning it on? I'd love a mount that doesn't get confused so easily

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Uri Abraham

Nov 16, 2020

Hi,

I am about to receive my CEM70G and your post are valuable to me, reading about backlash makes me nervous haha 😂😂

Thanks for your feedback Lorenzo and I will post my comments later on when I experiment with my new mount

Blue

Nov 17, 2020 · Edited: Nov 17, 2020

I have a CEM70G, I bought the G for the USB3, better integration of the electronics (One connection for everything on the mount) and I was setting up a second mount, one with a short focal length refractor and one with an SCT at approx 1400mm focal length. The inbuilt guider allowed me to avoid buying a second off axis guider and guide camera for the time being. The price difference between the CEM70 and CEM70G was about the same as a new guider setup.

The homing function is extremely handy. Power it on, find home and it is synced well enough to plate solve and sync using Plate Solve 2 near solving rather than having to blind solve for the first sync of the night. The iguider is perfectly adequate for my 480mm focal length, typical guiding is about 1" RMS on a reasonable night and i think it is hard to ask for more out of a 120mm FL guide scope, Min move in PHD2 is around 0.1 pixels! I get round stars in 600 second subs so I have no complaints there. I am also unable to crash my camera or scope in to the pier, the physical limits of the axes stop if before crashing the really expensive stuff. Better to need to replace the mount mechanics than the scope and camera if something goes badly enough wrong to hit the travel limits of the RA or Dec.

My only gripes at the moment are that the iguider requires the gain and exposure time to be set in the camera driver as well as the exposure time in PHD2, and that setting does not stick through reboots, and you can't select the home position as a park position (Something which will hopefully be adressed in a firmware revision) if you set the home position as park, it goes there but then does not stop tracking, offsettign the park position by a dregree or so parks it properly, but IMO it should be the default park position.

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NeedMoreCoffee

Nov 17, 2020 · Edited: Nov 17, 2020

I am also very interested in this.

the_bluester: sounds like you're very happy with your mount so far. Do you think the iGuider scope is good enough for a focal length of 800 mm? I have never done autoguiding before and am hoping I will not need a separate setup (one of the reasons I want to get this mount).

Thanks!

Blue

Nov 17, 2020

It would probably come down to your image scale. I see around 1" guiding, and maybe 1.2-1.3" on a poorer night, but my gear is imaging at about 1.6" per pixel so my RMS guiding error is less than one pixel on the image.

You would think 800mm focal length would be "Maybe" for the iguider. If you could do it with any of the multitude of 120mm focal length guide scopes then it would probably be OK, it has the advantage of solid mounting on the puck rather than flexure on top of flexure by putting a guide scope on rings or similar on top of an imaging scope.

Lorenzo Siciliano

Nov 17, 2020

Two questions: do you regret not getting the G version (with USB3 and wifi)? And I believe it has a home registration feature, so do you still have to be careful about homing it precisely before turning it on? I'd love a mount that doesn't get confused so easily

Hi.
I think the G version was not useful for me, as I use to do imaging at relatively long focal length (my range is 1000-1600 mm).
What I really miss is the wifi.
About that, I think this is a precise commercial choice: if you want wifi you must have the internal guider even if you don't want it. I simply disagree but, as said before, it's clearly a commercial choice: do you want wifi? Well, you must have internal guide too. But I don't need it! There's nothing to do: you MUST have it too! That's it.
Beside that, it's a great mount.
Ciao.
Lorenzo

Linwood Ferguson

Nov 17, 2020

It's not just Wifi, it's USB3, which I consider rather a must have for full frame imagers. I would also think important for planetary folks with high frame rates (though ROI restrictions can help there). Even if my lights are long enough not to matter, I don't want to spend an extra hour shooting flats due to USB2.

I really have no interest in the internal guider, nor Wifi, but USB3 is important. Also, I THINK they made a more rational connection of the USB ports generally. I plan to get the CEM70G just for that. They were very annoying, but wise – they collected stuff people might want more into the "G" version, even though the "Guide" part of the "G" was probably the least relevant to many.

Though maybe I'll put a wide angle lens on it one day and let the guide camera actually do some work, see if it's even in there.

Well, if I can find a CEM70G at all.

NeedMoreCoffee

Nov 18, 2020

You would think 800mm focal length would be "Maybe" for the iguider. If you could do it with any of the multitude of 120mm focal length guide scopes then it would probably be OK, it has the advantage of solid mounting on the puck rather than flexure on top of flexure by putting a guide scope on rings or similar on top of an imaging scope.

Thank you - that makes perfect sense!

barrabclaw

Nov 18, 2020

I agree that the single connection the G version gives would be nice. However, I'm not bothered by the USB2 hub. I have my focuser, filterwheel, and guide cam connected to the hub. None of those would benefit from USB3 as far as I can tell (use subframes with the guide cam to reduce any lag). You can easily run a USB3 cord through the center of the mount in about 3 minutes flat without modifying the mount in any way. So I have my main camera connected to that, whether for deep sky or planetary.

You could even have a USB3 hub on the scope with everyone connected there, and then connect to a laptop with USB3 run through the center of the mount if you wanted to save $400 and run everything on USB3.

The WIFI seems useless to me except for visual. If you're imaging with a laptop, you'll need a USB cable anyway to connect your gear, so you're still physically tethered to the mount. If you're using an ASIAIR, are you able to connect to the mount's WIFI and control from another device? Even if so, then the USB3 hub seems to be useless, since you'll just connect everything straight to the ASIAIR and not go through the hub.

I'd read some reviews on the stability of the WIFI before purchasing. Some users have reported that it's pretty flakey, although I don't have personal experience with it.

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Blue

Nov 18, 2020

In my case, the real selling point was being able to get the USB3 and "Single cable" integration of the on mount electronics at what amounted to the same price as I could defer buying a second off axis guider setup (And for me the second OAG and guide camera would cost about the same as the price difference between the CEM70 and CEM70G) It did cause a bit concern until the mount arrived and I could prove that the iguider was up to the task, but it has proven to be perfectly adequate.

I may even run a USB3 cable down through the middle of the mount eventually to separate the camera connection from everything else, but I am not going to do that until I have it on a permanent pier to save having a dangling cable on the mount when I have to carry it around each time I set up.

Jérémie

Topic starter

Nov 19, 2020

Hi @barrabclaw !
Apart from G / not G version (I understand you have the standard « not G » version), what can you tell about your experience with the Cem70 ? Are you happy with it ? Any Dec backlash problem as for Lorenzo ? Solved that problem ? Any interference between PEC and guiding or they works smooth together ? Maybe PEC is sufficient ?
Thanks for your feedback !

barrabclaw

Nov 20, 2020

In my case, the real selling point was being able to get the USB3 and "Single cable" integration of the on mount electronics at what amounted to the same price as I could defer buying a second off axis guider setup (And for me the second OAG and guide camera would cost about the same as the price difference between the CEM70 and CEM70G) It did cause a bit concern until the mount arrived and I could prove that the iguider was up to the task, but it has proven to be perfectly adequate.

I may even run a USB3 cable down through the middle of the mount eventually to separate the camera connection from everything else, but I am not going to do that until I have it on a permanent pier to save having a dangling cable on the mount when I have to carry it around each time I set up.

Sure, if you plan on using the iGuider instead of a short focal length guide scope, it could simplify things and you get a bonus in the USB3 hub. I don't think the iGuider would work well at my focal length (1000 mm) and I prefer using an OAG anyway. Also, you can't replace the scope or camera, but maybe iOptron wouldn't charge too much to fix it. Shipping would be painful though.

I just wrap the cable around the mount head when I carry it, but it's certainly not a necessity if you have the USB3 hub anyway.

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barrabclaw

Nov 20, 2020

Hi @barrabclaw !
Apart from G / not G version (I understand you have the standard « not G » version), what can you tell about your experience with the Cem70 ? Are you happy with it ? Any Dec backlash problem as for Lorenzo ? Solved that problem ? Any interference between PEC and guiding or they works smooth together ? Maybe PEC is sufficient ?
Thanks for your feedback !

I really like it. I get good guiding with my 190mm Mak-Newt, which weighs about 30 lbs give or take. I haven't noticed any backlash. Guiding Assistant in PHD2 measures backlash and tells me that its either undetectably low or 100-200 ms. I usually don't apply the backlash correction because I doubt that would make much difference. I haven't tried to use PEC. The periodic error of the mount is pretty low already, and I use the predictive algorithm in PHD2 that learns the PE to some degree. The rest just gets guided out. I'm not convinced that using PEC would be worth the headache trying to get it to work properly with guiding. I've written a lot more in a thread on CloudyNights under the same username if you want to look there.

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Uri Abraham

Nov 21, 2020

Hi,

I got my CEM70G two days ago, I haven't had a chance to image with it yet but I'm happy to share my experience so far.

The mount is very solid and very stable on the TriPier, the finish quality is good.
The TriPier itself isn't too friendly to setup, especially the lifting of the pier up and down, which causes the paint to peel off, it is very stable though.

First thing I noticed was a free play in the DEC axis which I managed to fix with adjusting the grub screw and the instructions in the manual.

One other problem I have is the mount not responding correctly to park command. It appears the mount keeps tracking after the mount parks and Voyager also shows its tracking. I'm almost certain this issue can be resolved with some change in the mount settings. Another aspect which bothers me a bit is the fact the mount can slew only a small degree beyond the zenith so the meridian flip becomes more critical by means of setting it up correctly, slewing manually beyond of course causes the gears to 'scream'.

I connected my camera (QSI683) and OAG camera (Starlight express Ultrastar) to the USB hub and experienced no problems at all. All plug and play with no drivers required.

Overall, I'm happy with the results so far and look forward for a clear night to further test the mount tracking and guiding. The intrinsic PE is +- 3.5 % according to iOptron so with my 910mm focal length OTA and OAG I am expecting guiding of 0.5" or below.

Will update you after several days of clear nights

Thanks
Uri

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Jérémie

Topic starter

Nov 21, 2020 · Edited: Nov 21, 2020

Thanks Uri, I am sure your feedback (this one and futures) will be very valuable for people thinking about getting this mount for Christmas 😉
Let us know more after a few more nights of use !

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Blue

Nov 21, 2020

Hi Uri, it is Paul M.

I assume if your mount is not parking properly you have set a custom park position at the home position? I reckon it if a firmware bug. Offset your park a little from the home position on both axis and it will park properly.

As for flips, they have not posed any problems for me, it can go well enough past the meridian to flip without issues.

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Linwood Ferguson

Nov 21, 2020 · Edited: Nov 21, 2020

Uri Abraham:
One other problem I have is the mount not responding correctly to park command. It appears the mount keeps tracking after the mount parks and Voyager also shows its tracking. I'm almost certain this issue can be resolved with some change in the mount settings.

I've read about that elsewhere, here's one mention and a pointer to a video, that suggests setting to 179 degrees; I do not have the mount so no personal info to share:

https://www.cloudynights.com/topic/715180-cem70-has-arrived/?p=10634427

barrabclaw

Nov 21, 2020

Uri Abraham:
Hi,

I got my CEM70G two days ago, I haven't had a chance to image with it yet but I'm happy to share my experience so far.

The mount is very solid and very stable on the TriPier, the finish quality is good.
The TriPier itself isn't too friendly to setup, especially the lifting of the pier up and down, which causes the paint to peel off, it is very stable though.

First thing I noticed was a free play in the DEC axis which I managed to fix with adjusting the grub screw and the instructions in the manual.

One other problem I have is the mount not responding correctly to park command. It appears the mount keeps tracking after the mount parks and Voyager also shows its tracking. I'm almost certain this issue can be resolved with some change in the mount settings. Another aspect which bothers me a bit is the fact the mount can slew only a small degree beyond the zenith so the meridian flip becomes more critical by means of setting it up correctly, slewing manually beyond of course causes the gears to 'scream'.

I connected my camera (QSI683) and OAG camera (Starlight express Ultrastar) to the USB hub and experienced no problems at all. All plug and play with no drivers required.

Overall, I'm happy with the results so far and look forward for a clear night to further test the mount tracking and guiding. The intrinsic PE is +- 3.5 % according to iOptron so with my 910mm focal length OTA and OAG I am expecting guiding of 0.5" or below.

Will update you after several days of clear nights

Thanks
Uri

I'm sorry you're having that problem. I haven't had any issues with parking, so it seems like there should be a way to resolve it - it's not a limitation of the mount, but possibly a problem with firmware or some setting.

For others that might be wondering, there are four pre-programmed parking positions - horizon on either side, and zenith on either side. You can also set your own user defined parking position. I've been able to use them all and I have NINA auto-park after my sequence is finished for the night. I'm confident enough with this mount now that I go to bed, let it image, and it parks itself before the sun comes up. No issues so far.

Guiding has generally been around 0.5" for me with 1000 mm focal length and an OAG. Payload is maybe 35 pounds with all the imaging gear. I also have the tri-pier which isn't as easy to setup as a tripod but also doesn't take very long. And it is rock-solid, so I'm very happy with it. I bet you'll get similar guiding results, Uri.

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Brian Sweeney

Nov 23, 2020

I have a CEM 70G being delivered tomorrow. Anything I should know for first time set up? Tips or tricks?
My previous mount was an Orion Atlas

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Blue

Nov 23, 2020

My tips would be, remember to start every session with seeking the home position (when powered on or any time you release the gear switches) and if you set a custom park position, don't make it precisely the home position as there seems to be a firmware glitch with parking right at the home position, offset around 1 degree in declination and it should park fine. If you set at the home position it will move to the position but then will keep tracking.

If you are going to use the iguider, the guide camera needs the gain set within the camera driver as well as the exposure time, I set gain to the mid point and exposure to -3 (Which equates to three seconds) and then you need to set PHD2 to three seconds. You need to reset the mid gain and -3 exposure each time you use it as that setting does not stick.

When setting the altitude as you do the polar alignment, the alt lock screws need to be firm enough that you can only just move the alt with your fingers, if the are much looser than that to start with it will move in both alt and az as you tighten them.

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Linwood Ferguson

Nov 23, 2020

I set gain to the mid point and exposure to -3 (Which equates to three seconds) and then you need to set PHD2 to three seconds. You need to reset the mid gain and -3 exposure each time you use it as that setting does not stick.

PHD2 can't control the exposure time? That's a pain, I frequently change guiding rate (i.e. exposure) in PHD2 during the night based on conditions, notably wind.

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