My iOptron 'little gem' GEM28 Report

[SteveNickolls]

I was able to image this week and try out the rearranged cabling hoping to use the USB hub on the ASI533MM Pro to connect the guide camera and ZWO EAF. The EAF worked well with control made using SharpCap Pro however SharpCap Pro was unable to see the guide camera with the cable arrangement so no dithering this time. PHD2 however saw the guide camera. 

During the imaging run until around 1.40 AM x56 frames with the OIII filter were taken so the GEM28 is proving itself for allowing a good widefield imaging set up with control at a considerable distance.

I hope to add more OIII data as clear evenings allow. This is the first composite image I've made from 102 x ninety second Ha sub-frames and x56 two minute OIII sub-frames, both with master flats and darks stacked in DSS and processed in StarTools, Starnet++ and GIMP.

Cheers,

Steve

Edited August 18, 2023 by SteveNickolls

[SteveNickolls]

September 2023 Update

I hope to continue posting data taken with my GEM28 set up to help inform prospective users and existing owners of the performance data obtained during imaging. This season I have had six occassions to image and these are the guiding values from PHD2 and which show consistency in the values obtained. iOptron states that the mount should have Peak values of <10"-

PHD2 RMS, Peak and PAE Values from GEM28 Imaging Sessions

Date	RMS		Peak		PAE
	RA	DEC	RA	DEC
7.8.2023	1.12”	0.78”	-4.71”	-5.71”	1.6’
15.8.2023	0.87”	0.89”	-6.40”	5.15”	1.0’
20.8.2023	0.87”	0.74”	-4.75”	4.81”	1.0’
21.8.2023	0.77”	0.57”	-4.05”	3.42”	0.5’
4.9.2023	0.92”	0.62”	4.37”	-6.04”	0.8’
5.9.2023	0.99”	0.85”	4.77”	-5.19”	1.0’

 

Cheers,
Steve

[Elp]

You're getting some decent results. It might also be advisable on what payload you're using. I've found balancing is extremely critical with this mount, a previous night I was using a custom camera lens setup so fairly light. But I couldn't get the Dec or RA balanced well at all, as a result doing 3 minute subs I had to discard around half the data as it couldn't settle properly after dithering, guide figures were also awful and you could tell by the guiding graph how it was struggling. Last night with a 7kg telescope setup and better balanced, best RMS I got was around 0.4, typical around 0.8 after dither settling, most 2 minute images were also good, need to check but I don't think there was a bad one.

As a comparison my hem15 was running the same camera lens setup, and guiding was typically 1.5 RMS, subs however were fine. Balancing on the HEM is only required in declination as the RA is a harmonic drive gear.

Edited September 6, 2023 by Elp

[SteveNickolls]

Hi Elp, thanks for your message.

These photos show the current payload on the GEM28, I recently added a Hyperpod unit to hold a ZWO EAF and a Williams Optics Vixen plate to give more space for fixing the Pegasus PowerBox Micro unit.

Typically I stopped weighing individual parts last season since the payload capacity of the mount (12.7kg) was clearly well in excess of the intended use it would be put to but my best guess is the total payload is modest at around 4kg plus cables. I do now use the original 4.7 kg counterweight for balancing.

As regards balancing I agree you have to work hard at it, I have found adding a spare Omegon Tri-finder (weighing around 210g) to the side opposite the EAF has helped balancing in the 'z' axis. It is my understanding that the internals of the mount head are not symmetrical and lead to imbalance in the 'z' axis'. In its design the mount can accommodate the iGuide accessory kit (weight 200g) on one side and think this is meant to help balancing on the 'z' axis without making the issue noticeable. I would suggest adding some mild additional mass on the side of the mount head where the iGuide accessory can be loated and see if this helps overall balance and performance. Your HEM with it's semi-harmonic gearing neatly side steps any RA issues with balance and is a nice feature.

The Samyang has the virtue of having just 135mm of focal length and with the ASI533MM-Pro the resolution of the set up is 5.74" per pixel the longest sub-exposures I've needed to take have been 3 minutes but apart from cloud spoilt frames I do not expect to get bad frames. Sharpcap Pro controls dithering and have not had issues relating to settling down at all.

If you do try to balance by adding a small mass to one side of the mount head I'd be interested hearing how you fare.

Cheers,
Steve

 

[Elp]

You're right, it should handle your setup fine once balanced, I did note the threaded hole on the one edge of the saddle which I believe is for the balancing kit, I did mount a small guidescope there once. My camera rig is mounted onto a custom dovetail setup I've put together in a cross formation, so I can mount one or two lenses and place the guidescope closer or further from the centre point as well as my airs, it works on my azgti as the Ra and Dec movement is quite stiff, it would however need modification if I use it on the gem28. The idea was to use the gem to try for consistent 5 minute exposures.

I have got a custom vixen clamp and threaded counterbalance weights which can be screwed into it for balancing my C6 when imaging F6.3 reduced.

[SteveNickolls]

I do like the idea of using two lenses on one mount to capture more data in the same time and have looked into the pro's and con's of it all. It would be very useful for making the most from our uncertain weather. Do you incorporate any dithering in the image capture sequence since one camera can be syncronised to the dither and will not lose sub-frames that way but the second camera will be affected?

Anyway I hope you can obtain better balance in the future and so lengthen your sub-exposure times and remove spoilt frames.

Cheers,
Steve

[Elp]

The main issue with it has been trying to get the second lens to align with the first (can be mitigated a bit if you use a larger sensor on the second lens). At first mounting parallel you'd think looking at infinity it'd be a similar FOV, it's not. So I've had to think of ways of mounting the second to an adjustable base so I can pan and roll it, then I can use plate solving and annotation to check the framing matches the first. Haven't really had a proper go with it yet, but the other reason of putting it together is so the hardware is fixed (no chopping and changing to suit other lenses or cameras, I just need to swap over tube rings or bases which all fit into the one Arca swiss clamp for the second lens).

It would also only really work if keeping the subs maybe below 2 minutes, otherwise the second lens will have too many waste subs whilst the first is controlling the dithering. If I were doing 3-5 minute subs I'd likely split them onto their own mounts, this setting up is also slightly faster (20-30 min per rig, or 30-60 min for the twin on one, the former at least one rig can be away imaging whilst setting the second). If the twin is already pre setup, there's no issue.

Obviously cost is also a factor with a twin setup, but I usually find I can experiment with one if another is capturing the important stuff.

Edited September 8, 2023 by Elp

[SteveNickolls]

Hi Elp, thanks for this practical advice regarding a dual rig set up. I had considered alignment of the two optics and there are a number of products on the market to allow adjustment of one of the pair.

https://www.teleskop-express.de/shop/product_info.php/info/p9974_TS-Optics-Dual-Mount---parallel-mounting-with-fine-adjustment.html  Price 285 Euros. You can get two of the adjustable units at more cost.

Avalon X Guider (c300Euro’s).

With both these you have the concern over balance.

 

Presently I'm at most using 3 minute sub-exposures and dithering every 2+ frames. With such a dual-rig arrangement this would have to be decresed in frequency. 

Here is my updated write up, it is based on my particular control arrangements but there might be somethnig useful in it for you. I don't intend going down this line despite the attraction of almost doubling available imaging time.

Cheers,
Steve

Project Tweedledum and Tweedledee.docx

[Elp]

Interesting read, I did look at those sort of adjustable mounts but they are pricey. Mines much much simpler, and having done my initial tests with the original that only had pan adjustment, I don't think it needs the tilt adjustment, just roll and pan. This is it ATM, I've since added a second finder clamp to the LHS so I can mount two asiair minis, you can also save a lot of weight and cost using uncooled cameras:

The beauty with this setup, if I'm only using one lens I can mount that on the RHS with the tilt mount closed, guidescope on the LHS and asiair in the bottom centre and it's fairly well balanced. Before when I was using cheese plates and stuff I had to keep taking it apart and reassembling to get the right balance. I might modify it further so I can add gimbal counterweights for further balance adjustment. I'll make a thread on this at some point, the project I was using it for remains unprocessed as I wanted to get more HA and RGB at the same time to finish it off.

Edited September 9, 2023 by Elp

[SteveNickolls]

Hi Elp, thanks for your feedback and for showing and describing your working arrangements. A picture paints a thousand words so they say. Nothing is going to happen fast here developing a dual-rig set up for use on the GEM28 but the potential to collect upwards of x2 the light in a session is a very strong motivator if money is no object.

Cheers,
Steve

[The Admiral]

On 08/09/2023 at 17:39, Elp said:

The main issue with it has been trying to get the second lens to align with the first (can be mitigated a bit if you use a larger sensor on the second lens). At first mounting parallel you'd think looking at infinity it'd be a similar FOV, it's not.

How far out are they? One would imagine that it ought not be too bad with wide-field set-ups. Mind you, with a 533 sensor the FoV isn't so wide field.

Ian

[Elp]

It's quite small, but enough that something like the heart and soul hardly comes into FOV (like it passes above or below it). I've tried a fixed pan, so next I'm going to try a roll and pan, if not that then a pan, roll and tilt. I want to try and keep it simple (and low expenditure as well as volume and weight) as I don't keep the image train fixed and swap out cameras and lenses. It is somewhat easier if the second camera has a larger sensor which is how I did it first as the second was full frame, but the aim is to use two of the same mono sensors.

Edited September 17, 2023 by Elp

[SteveNickolls]

November 2023 Update

Adding a 5.5" pier to the GEM28

I've recently purchased a 5.5" pier extension part from FLO to add to the GEM28 set up. After adding a long 290 mm x 90 mm William Optics plate to hold the imaging gear and Pegasus Power Box Micro unit there was a chance the plate could catch on the location of the mount's hand controller and top of the tripod legs so the next acquisition has been the iOptron 5.5" pier extension.

The extension comes in one piece, is made from aluminium and feels very sturdy. Also supplied are two hex bolts that connect the pier extension to the head of the tripod and an additional alignment peg which can be seen in the photo inside the plastic bag. This alignment peg should be fitted on the top of the pier as it is slightly shorter than the peg used originally on the mount. Don't take out the original peg to use it on the pier as I first did-doh! IOptron also make a slightly longer 8" pier extension shown below should your set up require slightly more room to operate-

Cheers,
Steve

Edited December 14, 2023 by SteveNickolls

[astrosathya]

Hi Steve,

This is by far the most detailed report I have seen/read. I am in Ashford, Kent and planning to buy a new AP Setup which is lightweight. I have been eyeballing the GEM28 for a couple of days. I used to have a HEQ5-PRO etc etc, all heavy stuff. 

I have read reports from India that the GEM28 has pointing issues, especially with Southern targets. Have you ever faced anything similar? 

[SteveNickolls]

Hi Sathya, thanks for your post. I've had the GEM28 for around 28-29 months now and apart from my recorded issue with the iPolar USB port the mount has performed well for me.  I haven't had any pointing problems, I use a combination of iCommander software and Stellarium to control slewing and both have worked fine. iCommander has the useful return to the Zero Position capability and Stellarium its useful planetarium. In addition I have used SharpCap Pro's 'go-to image' tool to slew to past positions to add extra data to targets.

I hope this account is helpful to you. Perhaps other contributors to this thread can give their views on the matter?

I can confirm the GEM28 is light enough to be readily moved into position each night.

Cheers,

Steve

Edited February 27 by SteveNickolls

[Ratlet]

I've not had any issues with the mount that weren't user error.  I often use a side by side mount which means the vixen saddle is 90 degrees from the normal position (if you consider normal as being pointing along the axis of polar alignment).  I didn't zero the position after swapping once and I came very close to crashing my camera into the tripod.  Entirely my own fault.  I now always set the zero position at the start of a session.

Edited February 27 by Ratlet

[Elp]

On 25/02/2024 at 09:40, astrosathya said:

I have read reports from India that the GEM28 has pointing issues, especially with Southern targets. Have you ever faced anything similar? 

It could be their polar alignment is off or location is not set correctly, either can make a difference as to the scopes pointing accuracy. I've only used the gem without a computer controller a handful of times and the target has always been in view close to the centre. Using an Asiair (for example other options are available) it a non issue as the air will plate solve and adjust the mount until target is dead centre.

Another issue you maybe reading about and not being specific about is the operational range of the mount is 10-70 degrees latitude. If the reviews you've read are from people using it very south in India and also Sri Lanka this may also be the cause.

[SteveNickolls]

Thanks ratlet and elp for helping answer Sathya's concern. 👍👍

Cheers,

Steve

[Cindyly]

Steve and friends,

This is such a wonderful thread! I just purchased a GEM28 and am learning how to use it. I own its little brother, Ioptron's Skyguider Pro, which I love but of course, it has weight limits. Seemed natural to go with something I was somewhat familiar with, thus the GEM28.

I've had it just a couple days, it's been raining here so I've been unable to give it a test run yet. Which is fine, I've been trying to get the integrated wifi to "talk" to my ipad through the recommended apps, but no luck yet. It's a work in progress, no doubt.

Anyway, I signed up to this forum just to say THANK YOU for the wonderful thread! I will reread it for the wealth of information it holds! 

Cindy in Maine, USA

[SteveNickolls]

Hi Cindy, thank you so much for your very kind post. Yes, it's usual to get rain after buying new astronomy equipment but hope that soon clears away so you can properly use the GEM28. I also hope you find this thread of continuing value-please do feel free to post any comments, successes, ideas if you can to help anyone else in the market and thinking of buying the mount. 

I haven't any personal experience in pairing the GEM28 with an iPad unfortunately and a lot of sleeps have passed since I looked into the wi-fi aspect of controlling the GEM back in October-November 2021.  When I first got the mount I did sucessfully try out all ways of controlling the GEM28 including wi-fi but that was to my laptop running Windows 10. subsequently I have moved to controlling the mount from indoors using USB over Ethernet which is very useful in the Winter. You likely know the wi-fi module for the GEM28 is located in the handset and is similar if not the same as iOptron's iStarFi adapter that other mounts have to add as a separate module. I think each owner finds the way that best suits their use of the mount and their circumstances and we amateurs are never afraid of trying out new things. 

Do let us know how you get on and we wish you clear and dark skies.

Cheers,
Steve

[Cindyly]

Thank you, Steve. The more I read about the wifi feature, the more I'm thinking it's just not worth the bother for me. I actually don't even "need" it, in fact I'd likely never use it, preferring to operate everything manually. I simply wanted to try it out "because it was there". 😆 

I have this thread bookmarked and will check in often. Also, I appreciate the invite to chime in with my own experiences with the GEM28, and you can bet I will do exactly that. I very much look forward to getting out there and trying this baby out! 

 

[Cindyly]

FINALLY, after many days of clouds and showers, I was able to take my new GEM28 out last night. I was very impressed. 

First, my operator error. There was one hour on Tuesday when the sky was partly clear (that didn't last, of course), so I did a very quick test run with it just to see how similar it was to its little brother Skyguider Pro. After polar aligning, I selected a star to slew to. The scope pointed below the horizon. When I checked the listed stars, very few were in my night sky. What the heck??? Something was very off. The clouds came in, and so did I. In my living room, I checked all my settings (time, location, etc.) because I suspected something was very off. Sure enough, my UTC time was set to +300 minutes instead of -300 minutes. The mount was pointing to stars in the Russian sky! I'm laughing at myself. 

Last night went very well, much better than I'd anticipated. The mount is a breeze to manually polar align, however I should add that I've had lots of practice aligning using the Skyguider Pro. One thing I noticed is that the reticle shown on the handset is a few degrees off from what the Ioptron app shows on my ipad. Since I know the app is very accurate from past experience, I used that to align in lieu of what the handset showed. 

I then slewed to Sirius. It got me in the ballpark. The red dot finder on my 6se OTA was off, so I had to fiddle around trying to get Sirius in my FOV. For some reason the handset said "No bright stars to see" or something to that effect. I'm presuming this reflects how off I was from my target. So I slewed to Jupiter, nice and bright. After a few attempts to get it in my FOV, I synced to it, then adjusted my red dot finder while testing to see how well the mount held Jupiter in place. It seemed to stay dead on. So I tried the goto, slewed to M82. By gum, the mount put it almost dead center. 
 

So now to test the tracking. I attached my DSLR to the 6se, set to DX, for a focal length of 2250mm. Nothing like diving in head first, ha. I figured if I could get 1 minute exposures without trailing, I'd be happy. Stars sharp after one minute. Tried 90 seconds. Stars still not bad, the larger ones not perfectly round. Went to 2 minutes, started to see a wee bit of trailing on the outer edges. Even my test shot of 3 minutes showed fairly decent stars near the galaxy. I think these results aren't too bad considering the focal length and no guiding. Needless to say, I was overall pleased. 

That said, when I then slewed to another target for another test, I must have somehow turned off tracking. I think that while trying to change the slewing speed, I must have hit 0 at some point, which I believe turns the tracking off and on. By then my fingers were getting cold (27F) so I decided to call it good and considered the evening a success. For now, I'm blaming any glitches on operator error. I'll be out there on the next clear night, hopefully on Tuesday if the forecast holds. I've read all sorts of issues that people have reported with this mount so I remain a bit cautious, but so far, I'm quite happy with it. 🤞🏼 

Cindy

Here's a 90 second jpeg of M82 straight out of the camera. 

 

Edited March 9 by Cindyly
Clarification

[Elp]

Pretty good feedback, I haven't dared attempting long focal length untracked though I have done 1000mm autoguided with the C6 which was alright, you have to get the declination balance pretty spot on (as you also have to do with the Ra). It's quite difficult as the mounts axis are very smooth and sensitive to fractional mm balance adjustments when unlocked.

[Cindyly]

I totally agree with you, Elp. I normally wouldn't have tried such a ridiculous focal length, but since I don't know any better, I gave it a whorl. I like testing limits, and this experiment let me know the outer boundaries of what this mount can do. Inexperience (or ignorance? 🤣) can sometimes work in my favor in this hobby, ha. I know nothing about auto guiding, or connecting to computers to control my gear, nor do I own any technical peripherals. This suits me just fine because I wouldn't know what to do with any of it anyway. I'm a pretty simple gal. 

[SteveNickolls]

Hi, thanks for your feedback on first using the GEM28, your results with such a big fl are especially very encouraging. As Elp mentions the axes are very sensitive to imbalance and its my suspicion the internals aren't symmetrical-the GEM28 has connections for an iGuider which I think helps balance things.

Enjoy what you have and I hope you have more clear nights to image and test things out. I did find moving from having to star align the mount to plate solving quickened the set up time and it can be done from indoors. Getting out under the stars can be good fun too.

Cheers,

Steve