Gem28 or HEQ5 with Rowan mod

[Doc817]

Hi all, 

Looking to upgrade my mount currently AZ GTI and I've narrowed it down to these 2 but I don't know enough about the GEM28 to make a fair comparison. So if anyone has any experience with both your views are welcome. I'm currently using WO ZS73III and a canon 550d modded but am in the process of getting a ZWO 183mc Pro so my pixel scale is changing from 2.06" to 1.15" so getting the best guiding is my main concern. I use NINA for all of my needs PA, imaging plate solving etc and use the pegasus pocket powerbox advance v2 to minimise cables running down from the mount. 

Thanks in anticipation 

Andrew 

[Elp]

I think you might be thinking about it too much. I use a Z61, 183, azgti primarily and generally don't have an issue. Guiding is typically around 1-1.2 RMS, the best ive had is 0.4 with an OAG.

To answer the original question, the gem28 in comparison is another kettle of fish entirely. You'll appreciate how much quieter it is (it's almost silent other than an electrical whine when it's moving) and guides very well. Balancing in Dec is a bit more difficult as it's very smooth (with the azgti is very easy due to the stiffness of the movement).

The only thing I don't like is it's another thing to carry out and bring back in as well as needing a bigger tripod than my azgti setup so a second thing to carry out, with the case and counterweights it's around a 15Kg carry, tripod another 5-6Kg. With the azgti its already all inside one bag to carry out and setup.

[Doc817]

@Elp Thanks for the reply and your feedback.

My guiding with my AZ GTI is about .8 to 1.3, but I think that can be improved if I wasn't using the SW wedge and instead with the WO wedge. It does jump to 1.6 after a filp and takes a while to settle and again it jumps after a dither. However I do not want to fork out for the WO wedge to find out that I should have just replaced my mount with either the GEM28 or HEQ5 with Rowan mod.  I am more than happy with my current setup while using it with the Canon 550D.

However I do think I am best to try and rule out living on the edge of possible issues that I might have tracking while using the 183MC Pro.  The reason you may not be seeing any issues is that the ZS61 has a shorter focal length than the ZS73 therefore your resolution is 1.38" per pixel which is why you do not seee any trailing with your images when guiding at 1.2 RMS.  While I may start getting the signs of trailing with a resolution of 1.15" per pixel when guiding at over this pixel scale.  Thats my understanding of it.  As for setting up I do all my imaging in my garden so that is not an issue for me.

This is in no way saying I am unhappy with my AZ GTI, I just think this upgrade in camera would be beyond its capablities and I am asking in peoples opion whats better the HEQ5 Pro with Rowan upgrade or the IOptron GEM28.

[Ratlet]

Can't comment on the HEQ, but I use the GEM28 exclusively for imaging.  It's pretty decent imho.  They updated the control software for it recently and it is much more reliable (so if you are looking at reviews, ignore anything relating to icommander connection issues from before August 2022).

It is incredibly quiet as elp mentioned.  There are a couple niggles, the ipolar uses one of the old style mini usb cables and there bolts to attach the mount to the tripod are hex head (I swapped mine out for cheap eBay knurled knobs).

I mostly image at 300mm focal length, sometimes up to 650mm.  Not had any issues with trailing stars due to guiding issues unless my guidescope has dewed up.

[Doc817]

@Ratlet Thanks for the feedback, do you use the Wifi or USB to connect to the iCommander?

[Ratlet]

USB.  I've never tried the WiFi though.  My paranoia is massive lol.

[Doc817]

LOL Thanks

[Stefek]

I had Rowan upgraded HEQ5 . Decent mount. Now i have GEM28 , (with encoder though). GEM28 is lighter, more modern design and is veery quiet (can't say that for HEQ5, even with Rowan. ) GEM connects reliably via both USB and and WiFi. iPolar is nice, it works, although I use NINA for polar alignment which is more accurate, so it is for me redundant.  Can't comment on guiding performance as I do not guide with GEM28 (encoders do their job quite nicely). In summary , two similar mounts, but if I would be buying now, I would go for iOptron, because it is lighter, quieter and more modern.

[SteveNickolls]

Hi, thanks for your posts. I can't speak for the SW HEQ5 but I have a thread on the iOptron GEM28 you might like to wade through, it's a 'warts and all' report-

I've had my GEM28 since October2021 and have got on fine with it. I'd imagine it's a lot quieter in operation than the SW model and easier to move around. The set up I use overcomes the fact my imaging pad is set up at the bottom of the garden each night so I employ USB over Ethernet as documented above. I can thoroughly reccommend the Star Tech hubs, simply plug and play. I have recently added a Pegasus PowerBox Micro unit which is proving a cracking buy in distributing power to the mount, main camera, StarTech remote hub and dew heaters. I had no issues with either iCommander 7 or 8 and was able to use the mount with the hand controller, by USB cable and wirelessly but have moved on to USB over Ethernet as I mention. It was a labour of love originally sorting out the iOptron software (basically poorly described in the manual).

I'm shortly going to add some data from PHD2 into the thread which I've been able to gather ovr the last week of clear skies. Basically I think I have a decent example of the GEM28. The two issues that spring to mind about the GEM28 were the scuffed tripod legs and the iPolar. I have since moved over to using SharpCap Pro's polar alignment so could have saved a few hundred pounds. My view of iOptron and software has steadily improved over time but their lack of an Android App to control the iPolar is verging on criminal but from what I've gleaned they can't create an App so it's waiting on an 'add on'. I decided to jump ship to the SharpCap Pro polar alignment tool.

I hope this and the other comments to your query will help you on making a decision. I did note the price of the GEM28 had recently gone down at FLO.

Cheers,
Steve

[Doc817]

@Stefek Thanks for that, really helpful.

I read alot of variation on the payload capacity for imaging isn't what ioptron state it should be can you confirm what your experiences are?

[Stefek]

23 minutes ago, Doc817 said:

@Stefek Thanks for that, really helpful.

I read alot of variation on the payload capacity for imaging isn't what ioptron state it should be can you confirm what your experiences are?

I usually run Esprit 80 , with autofocuser, 2600 camera, and 1kg heavy mini PC mounted, so all together around half of  iOptron max specification.  With only encoders with no additional guiding, I can make 5 or even 6 minutes frames. (did not try longer) Sometimes I also put Celestron C8 (2m FL) , which brings it up to almost 9 kg and still can make frames up to 120sec. with no wind) . So, from my experience with 2 different iOptron mounts , one can run them (for astrophotography)  at 70% of max specified load.  without any issues. I belong to "traditional" school thinking that the mount is the heart of the rig and for photography , it should not be used with more than 60% of specified total payload. 

[Doc817]

@SteveNickolls Yes I have read your post a few days ago and thank you for you indepth detailed reporting, I look forward to seeing your guiding update.  As I use NINA for my PA I don't think I would go for the ipolar but in saying that the price difference is actually not that much so it might be worth it fr resale value.

@Stefek Thanks for the info on weight, and your input in payload capacity.

 

My delima is now this, Do I purchase a new GEM from Flo or, I am currently talking to someone about their HEQ5 with Rowan Mod which has only had 10 hours of use for a little more than half the price...

[Doc817]

Update, the HEQ5 with Rowan Mod that I was inquiring on has now gone.  So do I wait for another or buy new or take a chance on the GEM28 or just get a EQ6 R

Edited January 24, 2023 by Doc817

[drjolo]

I used to have ZEQ25 and CEM26 and found them a bit troublesome. These spring loaded worms are a nice way to get rid of play in the worm gear, but in the same time the worm gear is not rock solid. These type of mounts require real good balancing in three (yes - three) axes - so both RA and Dec, but also the tube must be symmetrically loaded along its optical axis. If you have for example finder scope at the side or heavy focusing motor it needs to be balanced on the other side of the telescope. 

I also do not know what type of motors are in GEM28, but in CEM26 stepper motors are pretty much downsized, and the microstepping torque is very susceptible for the actual worm gear spring loaded force. If you put there too much force, you will end up with backlash in Dec due to the fact that the torque at 1/128 microstepping is not enough to actually rotate the worm till the moment some amount od Dec corrections accumulate and the actual correction movement is done. But it often overshoots then. My friend that has CEM40 observed the same phenomenon, but in less extent. 

But eventually I balanced CEM26 well and adjusted worm gears spring load, then I was able to get RMS error below 1" when guided. ZEQ25 I had before had DC motors with encoders, and it was a bit crappy, because it was just loosing the encoder pulses. Pointing and guiding were problematic, and it never got back to the home position accurately. 

On the other hand my ten years old EQ6 does not have problem to get 0.6-0.8" RMS error even badly unbalanced. HEQ5 that I had before as well. There is some play in worm gears, but such static play is not a problem to guide with PHD2 for example, since the software can measure and handle backlash in Dec, and RA backlash is not an issue. 

Edited January 24, 2023 by drjolo

[Doc817]

@Elp@drjolo thanks for your feedback, I have to say I am leaning more to SW just with the history and any issues have all been resolved or there are fixes for. Thanks again