My iOptron 'little gem' GEM28 Report

[Cindyly]

Tonight promises to be clear so I plan to give my new GEM28 a second whorl. It'll be windy (March is known for its brisk winds here in New England), but for 'testing out' purposes, that's no big deal. 

A couple newbie questions for you seasoned folks. 

When transporting the mount from the house to the yard (just the mount head and the CW bar on the tripod, no counterweight or scope), is it best to keep the clutches locked so the mount doesn't swing around? Or should the mount be removed every time? Seems like extra steps, so I'm curious what others do. 

It seems that unlike the Skyguider, once everything is balanced, the GEM28 is not designed to manually point the scope on a target by unlocking the clutches. The clutches are strictly for locking the mount in its zero position, is this correct? I haven't tried locking the mount in any other position besides zero for fear of damaging something. 

Thank you for any feedback, I do appreciate it. This puppy still intimidates me a wee little bit, ha! 

Cindy

 

[Elp]

If it's pre setup I normally carry the whole thing out in one, clutches locked. It's advised in the manual if you're transporting it to have the clutches unlocked so the gears inside or whatever it is don't clash. 

There's no reason why you cant unlock and use the Ra and Dec manually but there are two issue with this, A. The axis don't have setting circles so unless you DIY some you don't know the Ra and Dec rotations and more major B. I don't think there are encoders in the mount so when unlocked the mount doesn't know where it is pointing so when you go back to imaging mode you'll have to reset your home position, I could be wrong on this last part but I have known on power loss the mount changes it's home position by 90 degrees in RA at times.

[Ratlet]

I always transport the mount unlocked because I'm paranoid and want the moral high ground if it breaks lol.

I usually balance it through the day in the shed then remove the imaging rig (marked up the dovetail so I get it in the right spot.).

When moving I put the Allen key in the hole and that locks... One of the axis in place.  That stops the counter weight swinging.

I think there is/was a gem28 with encoders, but I've no idea how you would use it manually.  The clutch doesn't really clutch.  It's more an on/off lock for the motor.

As elp said, making sure the mount knows where home is is important.  Always zero your home when you power up.

[Cindyly]

Thank you very much for your replies Ratlet and Elp, that helps a lot! The manual is not particularly clear or concise on certain things, the part about unlocking the mount seems to refer to putting it back in its case. I do recall reading somewhere about keeping the mount locked when moving it on its tripod, but danged if I can find or remember where I saw this. 🤔

That makes complete sense about not being able to manually point to a target and locking the position in place. I had suspected that the locks are specific to zero position, but thought I'd ask. My problem is, I have a pretty hard time figuring out which button will move the mount in the direction I need it to go while trying to get a star in my FOV during alignment. Up is not "up", left is not "left", etc.. I always seem to go off in pretty weird directions, haha! It's like I need to tilt my head 42° to get oriented correctly, and I'm not even sure that would work. It's my first major learning curve! I do understand the basics, I just need lots of practice doing it, learning to translate what I'm used to (an alt/az mount where 'up is up' and 'right is right') into what needs to happen on an equatorial mount. It'll come with practice, or maybe I'll figure out a trick that makes sense in my brain. Hey, it's all part of the fun, right? Ya can't take all the sport out of it, lol!!

 

 

Edited March 12 by Cindyly
clarity

[Elp]

I don't particularly "get it" either, it depends on your optics as to the perceived orientation and direction to move the Ra and Dec if youre using your visual sense. Setting the Ra and Dec on the controller should get you where you want to go or if you're using the goto catalogue. But I'm lazy and use an Asiair, it'll image what it's looking at, plate solve and make the adjustments to the mount to get the target dead centre every time.

If I can be bothered to do manual visual I use a manual alt az mount and star hop followed by much moving of the scope up/down/left/right until I see "something" whatever it may be, this however requires a clear forecast less clouds ruin the fun.

[Cindyly]

Some observations about my mount from last night:

1. My reticle seems to be slightly off when set at the zero position, maybe ~2°. So yesterday afternoon I placed the mount at one end of my hallway, leveled it,  and released the gear lock. I found the  "sweet spot" where the reticle was level by overlaying the 9 and 3 o'clock positions with where the wall meets the ceiling at the other end of my hallway, which I know is level (I checked). Strangely enough, I was able to lock the gear switch in that position. I then took a white artist's pencil and marked that exact spot on the unit for future reference, then unlocked it and set the mount to its zero position. 

2. Last night I went out to do more practice with the mount, despite it being quite windy (8-12mph). I was able to lock the gear switch exactly where my two white lines met, aligned with Polaris at that setting, then set it to zero position. Now to see if it really was aligned correctly. 

3. After a 1-star alignment, I slewed to Bodes galaxy. I took a 30 second test shot and was a little too far west. I then quickly realized I had forgotten to sync to my alignment star. I'm not sure how critical that missed step is. Moving forward, I did a quick plate solving to figure out where I was pointing. In my low-tech method, I use a dongle that accepts an SD card that is readable by my ipad. I took the card from my camera and then ran the image through Astrometry.net.  It showed me where I was in relation to other close known objects. After comparing it to my Stellarium app, I saw how far off I was from my target. It was just a matter of slewing closer to where I needed to be. Another 30-second test shot showed my object was now in the frame. 

4. The tricky part for me was figuring out where the directional buttons would take me, since everything was 43° askew because of my latitude. So I chose a slow slew rate and took my time learning what buttons went where. I eventually figured it out, but it's not at all natural for me, so this will be something I have to relearn every time. But it's doable.

5. My alignment, doing it the way I did, seemed spot on. I was able to get 2 minute exposures with no throwaways, which surprised me because of the very windy evening. That says a lot about the Literoc tripod, a sturdy beast. I didn't attempt 3 minute exposures because of the winds, in hindsight I wish I'd tried. 

So far, I'm very pleased with this mount and how it performs. In my research I had read less-than-stellar reviews about it, but decided to chance it anyway After all, it seemed all mounts had their detractors, including the HEQ5 that I had also considered. In the end I went with the lighter GEM28 and I think I chose well. It's easier to manage than heavier mounts, holds the payload I need, AND I felt it would be easier to learn to operate, since I have its little brother the Skyguider, also a great little mount. Now to get some clear, calm skies! 😃

Cindy

[SteveNickolls]

Hi Cindy, pleased you have devised your own means of setting a good 'Zero Position' to begin sessions.

The GEM has four RA lock positions-the 'Zero Position', an 'East', 'West' and storage positions. The 'Zero Position 'is the one with counterweights pointing straight downwards, the 'East' and 'West' positions can be useful when you employ the iPolar or some other polar alignment tool that requires you to move the mount by 90 degrees. Now I've found that these three lock positions are more felt by the fingers than can be visually seen-when the rig is in just the right location (be it the 'Zero Position' 'East', or 'West' position the lock will fully engage. It feels like a definite engaging clunk. Maybe it was designed that way to be able to feel the right lock position at night in the dark (and after all the lock knobs and mount are all black coloured)? Let's call it an iOptron feature.

Rather envious of your conditions allowing you to actually get out and use your mount-enjoy!

Cheers,
Steve

[Cindyly]

Hi Steve, thank you for that info about the locking options at East and West, I had no idea! Since I don't have the iPolar, I don't know right now what I might use the E and W locks for, but I'm glad to know about it.

I'm not sure why the mount allows me to lock it in a degree or two cockeyed from zero. It's possible the teeny off-center locking position is inherent in the mount, perhaps for the express purpose of getting a leveled reticle locked in. If so, something like this should be in the manual, it's pure dumb luck that I discovered it. 

I hope you get some clear skies soon! As the days continue to lengthen, soon it won't get dark here until after my bedtime. A night owl, I am NOT, ha! Daylight savings time is not my friend for this very reason. I could set up my equipment to work while I sleep, but I tend to stay awake wondering if my focus went wonky, etc.; typically I check on everything once an hour and make adjustments if needed. But I'll find excuses to get out there and do short sessions, such as try to capture the ISS or do some moonscapes and time-lapses. Even just to practice on improving Goto procedures is worthwhile. It's all fun! 

[Ratlet]

I had my Gem28 out last night for some visual.  A marked departure from my usual is the mount has been imaging only so far.  My other mounts are nowhere near enough to handle the TecnoSky 102ED so I'm a bit limited in choice!

Initially I got caught out because the ipolar wanted me to confirm positions which it has never needed before.  I got out quite late and had a busy day so the instructions on the screen didn't make much sense, but the with benefit of hindsight they are perfectly sensible.  In the end I just used some numbers I found on a cloudy night thread which I think corresponds to the middle of the sensor with no calibration.  Can't remember them off the top of my head, but they worked well.  Next time I'll do the proper alignment routine.

I decided to try and pair it with SkySafari on my android phone but could not for the life of me get it to work.  I managed to get the setup done but could not get Skysafari to assume direct control.  Again the middle of the night is not the time to try and resolve IT issues.  Honestly I think with some better prep work on my part I can sack off the mobile completely.  I found the tactile feedback of the hand controller miles better than working with a mobile.  Especially with gloves on.

In the end I did a 1 star alignment on Vega and was off to the races.  I managed 3 or 4 targets and it did a good job finding the targets.  I needed to sync on a bright star when moving to the other side of the sky but that is to be expected on a one star alignment (my experience of the azgti was even with 3 star alignment and perfect setup it would still get lost).  The tracking was good and more than adequate for observing.  A massive step up on the AZGTI.

One thing I hadn't considered was unlike the AZGTI the GEM28 is not fitted with coffee grinder motors and was whisper quiet slewing around.

Whilst superficially a mixed bag I'm actually really happy with the result.  The GEM28 is an excellent mount for visual, handles to 102ED perfectly.  I thought the ipolar and using a laptop would be a pain, but it doesn't take long and honestly it gives the tube time to cool down.  The goto is night and day compared to the previous cheap mounts I've used.  I'd even go as far to say I liked it.  The only real issues were attributable to operator error or poor planning on my part and could have been solved with some prep work (prepare an observing list with NGC numbers, etc.) and RTFM before using the mount.

I was previously considering an EQ5 with a tracking motor for the 102ED due to poor goto/controlling experience with the AZGTI and a celestron 127SLT I had a couple years back.  That plan is now on hold (and my bank balance breathing a sight of relief).

EDIT:  My only minor critiscism is that I had a habit of accidently hitting the back button whilst centering things.  I'm going to have a look at 3d printing some thing to make it clear which buttons are for direction and which are for menus.  Maybe a barrier or an extension for the existing buttons.   Also need to 3D print a holder or maybe just a ring to keep the loop on string on the handcontroller open.  A holder would be nice, but it hangs off the eyepiece holder perfectly well.

Edited March 31 by Ratlet

[SteveNickolls]

Hi Ratlet, thanks for sharing how you got on last night. Agree about night time not  being good for resolving IT issues. 😬 Was the issue with the iPolar down to new software? I've not used mine for a long while now preferring SharpCap Pro's polar alignment tool.

The GEM28 is indeed a very quiet mount and am really glad you have found you can save money not having to get another mount for your 102ED.

I presently use a holster that came with my CG-5 to hold the hand controller of the GEM28 but you could have a nice business selling printed adapters for the iOptron. 👍

Here's to more clear sky nights ahead.

Cheers,

Steve

[Elp]

I found ipolar straightforward, cant remember exactly the routine, does it need two or three Ra rotations first then you're presented with the red/green circle alignment routine?

The need for ioptron handsets to be plugged in is slightly annoying if using computer controllers, on my CF tripods I simply hang it off the centre hook, the coiled cable ensures it doesn't move down. With the default literock I suppose you can place it on the accessory tray? I've seen some 3D prints people have made of a holder which affixes to one of the legs and you simply plonk it in when not in use.

[Ratlet]

1 hour ago, Elp said:

I found ipolar straightforward, cant remember exactly the routine, does it need two or three Ra rotations first then you're presented with the red/green circle alignment routine?

The need for ioptron handsets to be plugged in is slightly annoying if using computer controllers, on my CF tripods I simply hang it off the centre hook, the coiled cable ensures it doesn't move down. With the default literock I suppose you can place it on the accessory tray? I've seen some 3D prints people have made of a holder which affixes to one of the legs and you simply plonk it in when not in use.

Aye. Every time I've used the mount previously it didn't ask for alignment just gave me the cross.  It was asking for the RA to be rotated but I kept thinking it couldn't possibly be that so gave up.  I was pretty tired by that point lol.  It was 100% operator error.  I know what I'm doing now so won't be a problem in the slightest.

I did have one of the 3D printed brackets but it wasn't great.  Wouldn't be hard to fix the design flaw.

I think hanging it off one of the screws on the 2" adapter would be perfect, just the little bit of rope wants to go flat so I need to open it which is very slightly frustrating with gloves.  Very slightly though.

To an extent I think I've been looking at greater automation (integrating wth sky safari) with my mounts to make it easier, but honestly using the hand controller was much better I think.  I'm still going to try and get sky safari to work, but ultimately doing some proper planning and making an observing list is what I need to do.  If you know the NGC/messier/etc number it's a doddle getting it to navigate with the paddle.

[SteveNickolls]

June 2024 Update

How time flies

It doesn’t seem possible but I’ve owned the GEM28 for a little over 32 months now, purchasing it from FLO back in late October 2021. Summary-for any prospective purchasers out there the mount has continued to work just fine for DSO imaging which is comforting to note. The data from the season's guiding shows a consistency of operation and performance well within the manufacturer’s specification.

There were far fewer occasions when the mount could be used this last winter because of persistent storms rolling in off the Atlantic one after the other. This did however give time to do some analysis of the mount and provide benchmarking data for future checks on the mount’s performance. I did post some guiding figures for six sessions back in early September 2023 but can now list below the guide figures for the whole period up to the end of January when rain and cloud ‘stopped play’.  The data is taken from PHD2 Log Viewer. For the three sessions that straddled a late night/early morning during January there are two sets of figures given, Ante-Meridian (AM) and Post-Meridian (PM).

 

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’
10.11.2023	0.98”	0.72”	6.23”	-9.89”	1.6’
14.1.2024 AM	0.92”	0.56”	-4.58”	4.75”	0.1’
14.1.2024 PM	0.95”	0.58”	-9.57”	4.89”	0.7’
17.1.2024 AM	1.04”	0.73”	5.22”	-8.98”	0.6’
17.1.2024 PM	0.94”	0.58”	-4.51”	4.44”	0.5’
30.1.2024 AM	0.96”	0.65”	-4.93”	-4.62”	1.1’
30.1.2024 PM	1.03”	0.76”	-5.53”	-4.24”	1.2’

 The averages for the season being-

RA RMS	0.95”
DEC RMS	0.69”
RA Peak	5.36”
DEC Peak	5.55”
PAE	0.9’

From what I’ve gleaned off the Internet from other users of the GEM28 that have posted information the discrepancy between the RMS values for RA and DEC with the GEM28 seem standard. Ideally they should be more equal in value rather than being 0.95” v 0.69” to yield rounded stars. However just using the Samyang lens at 135mm focal length guiding is not put under strain and both RA and DEC values amount in real life to just a fraction of a pixel, so no oblong stars anyway as might be the case if imaging at greater focal lengths. In the coming season I hope to have opportunity to image with a 400mm telescope and the guiding results and images will be reported back. It would be interesting if other users of the GEM28 could post their guiding stats to allow a wider evaluation of the mount’s general real life performance to be made from a cross section of owners.

Polar Alignment Error

As regards PAE the results from PHD2 Log Viewer showed a range of values throughout the season, with values between 0.1’ and 1.6’.

RA RMS	0.95”
DEC RMS	0.69”
RA Peak	5.36”
DEC Peak	5.55”
PAE	0.9’

I do wonder if the method of loosening and re-tightening the two hex bolts on the mount to allow adjustment in the mount’s Az to allow polar alignment contributes an error here? The mount is set up each session and I use SharpCap Pro’s Polar alignment Tool to perform the polar alignment through the main optics and camera. I always get the alignment into the ‘Excellent’ category according to SCPro but the PHD2 Log Viewer analysis is usually showing a much less accurate, on average 0.9’ or 54” polar alignment. I have used a procedure that starts with the counterweight set in the 90 degree position for the first polar alignment image using SharpCap Pro and then returning the counterweights to what will become the 'Zero Position' before taking the second image which you then adjust the mounts Alt and Az bolts to obtain an accurate polar alignment. I have tried not loosening the Az bolts but perhaps the bolts are not really tight enough to begin with and still allow some post-alignment movement degrading the accuracy of the PA? Really a better design of the fastening of mount to tripod could be had but this is true of other mounts in general not just the GEM28. With all this said I recall however that a PAE of less than 5’ is fine anyway. 

The Future

In the future, and I’m seriously hoping that we won’t have a repeat bad autumn/winter in 2024, I hope to continue using the GEM28 to collect more Ha and OIII data on a number of targets. 2023 really only allowed me to produce a single decent image combining Ha and OIII data of the flaming Star region in Auriga. This is from Ha and OIII data collected over the two year (2022-2023) period comprising x190 ninety second Ha sub-frames and 281 two minute OIII sub frames (4.75 hrs + 9.37Hrs respectively). The filters used were Astronomik 12nm Ha and 12nm MaxFR OIII. The online DeepskyDetail SNR calculator to help determine the amount of SNR involved, for Ha it was >100 SNR and for OIII between 70-80%. 

The calculator can be found here- https://deepskydetail.shinyapps.io/Calculate_SNR/

Updating software

From what I have gleaned while ASCOM has moved to v6.6 SP2 there is no need to update unnecessarily and recent updates of iCommander are mostly to include new strain wave mounts. This decision will save having to update mount firmware in the immeadite term and the consequent redoing settings in both SharpCap Pro and PHD2.

I am mindful of the changes Microsoft intends to foist upon users, with Win 10 being unsupported after October 2025 and the arbitrary pre-requisites placed on machines running Win 11 and Win 12. This will need more consideration in the coming season.

Good Luck

I wish everyone good luck (and better weather) for this coming season.

Cheers,
Steve

[Ratlet]

I'll add a bit on my experience, I've not gotten to use it much for imaging over the last year for much the same reason as Steve.

I have taken to not adjusting the azimuth  altitude after polar aligning and packing up.  This was handy yesterday as I used the mount for some solar observing and got the mount north-ish and the goto got it pretty close to the sun.

I did manage to find use for the Icommander app.  Once connected to the phone you can sync the location and time from your phone.  This is much quicker than using the handset.  I did my position adjustments and alignment sync with the handset as I find the lack of tactile response for steering to be intensely frustrating.  Personal preference though.

I did the actual observing with my 102 f7 and the mount handled it very well.  I did some imaging unguided of the sun and despite the gale there was only a little wobble.

 

Edited June 5 by Ratlet

[SteveNickolls]

Thanks Ratlet for your update on experience with the GEM28, it would be good to have a consensus over how best to aproach polar alignment bearing in mind the two hex bolts involved. I'm thinking my Az bolts may need niping up slightly then leaving them alone. 

Really pleased to hear your 102 works well on the mount that's great, encouraging news. I'm hoping to use my StarTravel 102 this coming season after doing some mods suggested by Martin Pyott in hiscrecent videos (replacement focuser and reducer/flattener).

Cheers,

Steve

[Elp]

I haven't used mine much since getting HD ones but off hand I believe my typical total RMS guiding at 200mm FL guidescope works out around 0.6-0.8 if theres little to no wind. With an OAG I believe it was even better but I haven't used the long FL setup for a while. The thing is you do tend to get reliable and consistent guiding with this mount as long as it's well balanced and on a good tripod.

Regarding azimuth locking bolts, I found once I've got a good PA (less than 50 arc seconds I usually do but with this mount can get to below 10 quite easily, using an Asiair so I take such figures with a dollop of salt), I just very loosely hand tighten them with the Allen key, like incredibly lightly, anything more knocks the PA out for six. It doesn't change the guiding figures during the session even though they're not tightened solid. My hem15 I usually don't even lock them, just make sure the adjustment knobs are flush against the azimuth pin.

[Ratlet]

Sorry, I realised I made a mistake on my previous comment.  I mean to say altitude bolts.  I get that dialed in on a polar alignment and then for visual it is close enough (so far) for visual.  I replaced the hex bolts that came with the mount with thumb screws from ebay.  I think they were M6 but would need to double check.  Thumb tight works perfectly for securing the mount to the tripod.  For a good PA I usually get the bolts that secure the mount tight, but still with a bit of play, dial in the azimuth as best I can, tighten the bolts securing the mount to tripod the rest of the way.  If the polar alignment drifts after this I can back them off slightly and adjust the azimuth.

All in all it is a more pleasant experience for visual than the azgti and a mobile.

[SteveNickolls]

Hi Elp and Ratlet, thanks for your feedback experiences using the mount and especially those hex bolts. The GEM 28 is coming over as a decent mount for its price but of course now faces some serious competition from the plethora of lightweight strain wave mounts (and iOptron makes plenty). I will try and source the right thumb screws as it will let me do away with the hex key which is always carried along with the mount.

Thanks again,
Steve