How Good are iOptron Mounts

[Hans Tucker]

I am looking at building a portable imaging rig and have been eyeing the iOptron GEM28 Mount but looking at Sidereal Trading prices for this mount it isn't exactly cheap depending on the options. So how good are iOptron Mounts mechanically and Goto Software?

[RKenning]

https://www.cloudynights.com/topic/761173-ioptron-gem28-first-impressions/

[gregbradley]

What exactly does < +/- 7 arc secs PE mean? Does it mean 14 arc secs accuracy? Or does it mean 7 arc secs peak to peak?

For example Software Bisque say their MYT mount is a maximum of 7 arc secs peak to peak which is clearer as it means the total PE not half of it.

Greg.

[JA]

Hi Greg,

I would take it to mean <7 arcseconds either side of some nominal point (possibly the mean), so that would make <14 arc seconds peak-to-peak. The specs that I saw for this mount, did however state it as <±10 arcseconds PE, making it <20 arcseconds PE peak-to-peak. The Cloudynights review above (thx Robert) shows guided tracking error results of ~0.5 Arcseconds for RA & DEC.

Best
JA

[gregbradley]

How meaningful though are these 0.5 arc sec guiding accuracy. Surely that is a reflection of the focal length and pixel size of the guide camera.

If its measured using an OAG that gives it a bit more reference but if its using a guide scope then the units of measurement would be different or don't I have that right where arc secs is arc secs regardless of pixel size and focal length?

Greg.

[The_bluester]

If you plug the right guide cam pixel size and guice scope focal length for your system into PHD2 (Be that a guidescope of some sort or an OAG) the guiding figures refer back to a real number in relation to the sky. Probably other guide software does the same but I have only used PHD2 for guiding since I started imaging.

[JohnH]

Hi, I recently bought a CEM40EC for the same purpose - I wanted a portable setup, I wanted to be able to image without guiding when mobile hence my selection of the EC option. I am very happy with it. Tracking and goto are accurate. Polar alignment is very fast with iPolar. You can see some images and tracking logs here:


https://groups.io/g/iOptron/topics


The fit and finish are good.

[gregbradley]

I was wondering what the EC model was and why it was so much more expensive so encoders eh? That seems cheap for encoders. DO they allow unguided imaging?

I am looking for a portable mount.

Greg.

[lazjen]

iOptrons EC model use relative encoders. It is possible to do unguided imaging but I don't know the boundaries/limitations for that.

I am reluctant to recommend iOptron mounts with encoders because I do not believe iOptron's support and software/firmware development is of a suitable good standard. Which is a shame, because the hardware itself is generally pretty good.

I've got the CEM120EC2.

[gregbradley]

Thanks Chris.

But you find the guiding to be good which is what we want at the end of the day.

Encoders sound good but its another layer of something that can go wrong unless they improve guiding substantially.

Greg

[JohnH]

There is a lot of misinformation/commentary or at least out of date information out there. My mount is an EC model, it works very well. I can guide it when at home and use it unguided when mobile.



The encoders being relative is not an issue unless you intend to put the mount in a remote/automated setup.


As for how long you can run unguided - well it depends of course to give the consultants answer. If your PA is good and the imaging scale not to fine then 3-5 mins should be achievable.



You can see some traces from my mount both guided and unguided plus and image of Eta C taken unguided from my home site (Bortle 8 inner west Sydney).

[lazjen]

At least for the CEM120EC2, the relative encoders and remoteness are not a problem as you can always "seek the zero position".

I also get good guiding results (using PHD2) and my results are essentially bound by the seeing in the area. I remember doing some unguided tests a while back (at 700mm) and I think I got up to 10 min ok.

To explain further on what I was talking about re: firmware/software. The CEM120 models have details for a pointing model, but it's never been implemented. There are bugs related to guiding at fast rates (from memory < 2s) - I generally use 5 sec so I'm not too impacted, but it would be nice to calibrate PHD at a faster rate. GPS issues - I'm not sure if this is software/hardware at root fault, but software should be better to handle failures (it sometimes fails to lock on to satellites for a fix and I assure you I don't move my dome that contains the mount).

These issues (and more) have been reported to iOptron but we've seen no updates for over a year now.

[gregbradley]

Thanks for the info John and Chris. Most helpful.

That's a pretty tight guiding graph there. Looks a lot like my PME's.

Greg.

[lazjen]

Here's an example of my guiding from the other night. Conditions started deteriorating further soon after this:

277831

[Logieberra]

I have a CEM70G. It’s so close to my old MX in spec and tech features, that I’d have a lot of trouble paying full price for an SB mount ever again… 7arc/sec or less peak to peak.

[Logieberra]

That’s their GEM design. The CEM is superior in PE from what I’ve seen. Check out the new CEM26 (baby CEM70 design); or CEM40. CEM70 is portable as well IMHO…

[gregbradley]

Quite good but some fairly large spikes. Do you use PPEC?

Greg.

[billdan]

Those large spikes are from Dithering followed by Settling time.

[lazjen]

No PPEC for mounts with the encoders.

As Bill mentions, the really large spikes are around the dithering.

If you weren't referring to those, then the remaining might be an artifact of the graphing given the time scale. You can see there's very little corrections going on (the tiny little vertical spikes shown in the graphs).

Finally, I might have not (re)checked the DEC balance after doing some changes - I've noticed I get much better results if it's really well balanced for DEC.

[gregbradley]

No I realise the really large spikes are from dithering I was referring to compared to the main graph larger spikes.

Still in the scheme of things relatively small spikes.

Are you getting round stars in 10 minutes with say around 1200mm focal length?

That's the bottom line.

Does the mount have a home switch or isn't that needed with encoders?

A home switch is one feature I really like about Software Bisque mounts.

Greg.

[lazjen]

I have got round stars at approx 2000mm focal length - from memory though that was 5 min exposures. I should do some more testing sometime, but I doubt I'll have problems at 10 min.

I'm not sure what the home switch is, but the mount has a concept of a zero position. Part of the calibration process for the encoders includes it searching for the zero position. In normal usage, you can tell it to go to the zero position and then the relative encoders work from that (AFAIK). Perfectly usable for remote setup.

[The_bluester]

I don't know for sure about the EC mounts (I think they do) but my non EC CEM70 has homing sensors.

[gregbradley]

Yes that is what I was referring to. Software Bisque and AP call it a home switch but its a reference point that aligns the scope so its ready to do go -tos.

Greg.

[Logieberra]

Greg - it’s the same thing as your SB mounts - except iOptron’s homing is it’s “Zero Position”. The ZP is the position where the counterweight shaft points to ground, telescope is at the highest position with its axis parallel to the polar axis and the telescope is pointing to the Celestial Pole. You need to reset the ZP every time the clutches are disengaged.

At the end of each session, I park in the ZP.

Shame our APs don’t include homing switches/ZP…

[JohnH]

You can set and goto the ZERO position (thus you have the encoders set to match the CW down position). You also calibrate the encoders from that position. I always goto zero at the end of a session but you can also park at other positions if you want to and the mount will know where it starts from which makes more sense for permanent set ups.


https://s3-us-west-1.amazonaws.com/groupsioattachments/4324/84372824/1384/0?AWSAccessKeyId=AKIAJECNKOVMCCU3AT NQ&Expires=1626993345&Signature=TzoXAVgOjxU7trH9x4NxfhbTv Cg%3D

[gregbradley]

Sounds good and yes I would like that facility on my AP. I think it is available as a kit if you have the latest electronic controller.

Greg.