I own the iOptron GEM28 now for more than a half year. The first 3 months were horrible in terms of guided DEC performance, until I found the proper gear meshing and axis stiction by try-and-error. Now I’m satisfied with the guiding ๐Ÿ™‚

Read more about my attempts here:

Unpredictable Freezes

However, the annoying freezes of my GEM28 still occur. This is how such a freeze looks on a single exposure:

I notice a freeze when some of the direction LEDs of my MGEN light up constantly and the guide star starts to drift in one direction. From that moment on, my GEM28 stops to process guide signals.

The hand controller also usually no longer reacts to any commands. Sometimes even “back to zero position” doesn’t work anymore.

I replaced the MGEN cables, did a MGEN reset, upgraded the GEM28 and MGEN firmware, used different power sources… nothing seems to eliminate that unpredictable freezes.

I’ve to check every 2-3 shots if the mount is freezed again. If so, I can reset everything as follows:

  • Stop guiding
  • If possible back to zero position by hand controller or if that doesn’t work, manually to zero positionโ€ฆ I already had both circumstances!
  • Power off / power on
  • Star alignment
  • Back to my target and hopefully catch the same field of view like before the freeze
  • Guider setup
  • Start shooting again

This “reset” takes around 10-20 minutes and is super annoying! The problem only seems to occur when ST4 is used for guiding (according to many cloudynights postings)! There are people without such problems, but they all using ASCOM. Even with ST-4 some people reports no problems.

It’s a pity! I like the GEM28 for it’s weight and payload capacity (and also the look-and-feel). Without the freezes the GEM28 would be a fantastic portable mount!


Within total 25 sessions my GEM28 had 7 freezes (as of today, February 9, 2022). This is anything but reliable!

Update May 3, 2022:

No problems with my GEM28 the last 12 sessions. I’ve no explanation… Hope it stays that way!

ASCOM instead of ST-4

I contacted iOptron regarding the freeze problem and they suggested to use ASCOM instead of ST-4 for auto guiding, but this is a no-go for me, since I still don’t want to use a laptop for my astrophotography sessions. For this reason I ordered the AccuAlign version instead of iPolar at the time… and I still want using my DSLR, triggered by MGEN.

And now iOptron tells me indirectly to use a laptop… hmmm… No! The GEM28 comes with a ST4 guider port, so I want to be able to use it!

Hopefully iOptron will patch the ST-4 freeze problem with an updated firmware soon!

Don’t get me wrong: if you use ASCOM for guiding or even your GEM28 work constantly fine with ST-4 guiding, you’re a lucky guy.

I am not! And I know for sure, I’m not the only one with exactly the same freeze problem!

Star Adventurer GTi

Maybe a light on the horizon?

I’m very curious and looking forward to the lately announced SkyWatcher Star Adventurer GTi! It comes with all the features I would have liked to see on the original Star Adventurer.

Motors on both axes (RA/DEC) and GoTo, but (unfortunately) still
5 kg payload capacity.

Announced for May 2022!

So, iOptron has time to fix it before the GTi release… ๐Ÿ˜‰

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  1. Timothy

    Hi, nice site, I’m Tim, I live in Ticino, and I also like AP, I was looking for a portable setup, I have an EQ6-R in my balcony at home but for a portable setup, it’s pretty heavy. I was looking around on a GEM28, and I dall into you website, lol. ๐Ÿ˜… Would you buy again today the GEM 28? I saw it on couple of astro shilop in CH available, and I think could be the best mount for price/weight setup…. Did you used with the PC instead of ST4? I would use it only with PC or PI..

    Thanks for any support or tips CS Timothy (www.timopro.ch)

    • star-watcher

      Hi Tim
      Thanks. Difficult question… I like the GEM28 for it’s portability and payload capability. But the freezes are very annoying. I check every 2-3 shots the guide star position to be able to react as fast as possible if a freeze happens. Thats the only thing what makes me think I would not buy it anymore today. Unfortunately there is no alternative in terms of mount weight and payload capability… and other users seems to not have the freeze problem (especially when guided by ASCOM). But I know for sure a second person with the same freeze problem (also ST-4 guided). So it looks like there is really a problem with ST-4. So far I never tried ASCOM since I don’t own a laptop for this.
      If you don’t plan to use ST-4 anyway (as you wrote), I would take the GEM ๐Ÿ™‚

  2. Michi Z

    Sali Tim,

    any recent FW update solving your st4 issue?

    Just deciding for my first (used) mount and the gem28 could make the race for that portable cityscape night out capability.



    • star-watcher

      Hi Michi
      I guess your question is addressed to me. If not, I apologize ๐Ÿ™‚
      I’ve upgraded the firmware once, but no changes in terms of st-4 behavior afterwards. Still unpredictable freezes/crashes… sometimes my GEM28 suddenly stops reacting to auto guide signals. Nevertheless, I like my GEM28. Leightweight with GoTo and a max payload capacity of 12kg. But no clear skies since months here… ๐Ÿ™

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