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iOptron GEM28 experience sought

iOptron GEM28 Equipment Equatorial Mount Buying Advice
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andrea tasselli avatar
andrea tasselli avatar
Hello everyone,

I am looking at a GEM28 and I have no idea of its actual performance under the sky expecially from anyone having used it for quite some time. Pros and cons, defects to look for and issues in actual use would all be welcome. I also discovered to my horror that it hasn't got clutches so its direct drive from payload to worm. Does this bother anyone in actual practice? All info gladly received!

Thanks

Andrea
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Morsing avatar
Morsing avatar
I have one, but I have only had it for a few months, and weather has only permitted me a few outings. I have nothing to complain about in terms of build quality or ease of use - very good and simple.

I am guiding with a 162 mm guidescope with a 120mm mini through a ASIair pro. It was completely plug and play. Guiding in RA is 0.5-0,9" in my terrible seeing conditions. However I have lot og DEC backlash/sticktion, that I have not solved yet. If I misalign the polar alignment a bit and only guide in one DEC direction, I get very good guiding of 0.3-0.5", for a RMS total of around 0.5-0.7", far below my imaging scale of 2.6". If i polar align well, which is very easy to do with the ASIair pro, and let DEC guide i both directions, the backlash gives me guiding of around 1.5", which I am not happy with. I still have a few options to try out to fix the problem, one being binning the guide cam to avoid chasing the seeing and the other being a resetting of the DEC shaft, which I am apprehensive about performing myself.

That said, I have not missed a single sub due to guiding with my 300mm FL / 2.6"/px imaging scale. I would just like to use a longer FL at some point in the future! 

I don't think the direct clutchless connection is a problem - there is no play whatsoever. But of course one should avoid hitting the payload...

Oh, and meridian flip works like a charm and guiding resumes automatically.

Overall, I am happy with the GEM28 for the price, but would like to tweak it a bit more to achieve sub arcsecond guiding WITH good PA!

BR
Morsing


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