Some thoughts on the new iOptron GEM45

[The Admiral]

I recently took delivery of this mount, having until now only used an Alt-Az mount for imaging. So this is a whole new experience, and as such I’m not really in a position to give a meaningful performance review. Nevertheless, here are my first thoughts.

I wanted a mount that could be set up for each session, and light enough to allow my ageing frame to be able to carry it from inside the house to outside. It also had to be able to successfully carry a load currently around 6-7kg without complaint. So this is what attracted me to the GEM45. I bought the version with the case and tripod, non-EC. I don’t guide it as yet, so I can’t quote chapter and verse on its guiding performance.

Here's the set up raring to go! I've left the tripod trousers on!

 

First impressions.

It seems a solidly built, well finished, precision machine, unlike what one would expect from a mass-produced object. The axes move smoothly and I haven’t noticed significant backlash either by ‘free play’ or other than instant response to commands when lining up objects. However nice the looks, performance is everything of course, though it does give confidence.

The first thing I needed to do was to swap the latitude adjustment from the low position to the high position, as I live in the UK. It is worth noting that for where I live, ~51° N, I need to wind back the altitude to ~40° with the altitude adjuster (not re-set the setting from high to low, fortunately), each time I need to get the mount into the foam cut-out of the case.

Initially I had trouble locating the bolts with which to bolt the mount onto the tripod, the Azi Locking Screws. Thanks to FLO that was simply resolved, but I found that one of the bolts was slightly bent, enough to bind a bit in the thread, again resolved by the excellent services of FLO. Also, these bolts are meant to be used with the provided washers, but only one could be located. These are little perishers, as it’s easy to drop them when assembling the mount, as I discovered. My wife’s eagle eyes managed to spot it on the patio; try doing that in the dark! It’s a pity that the bolts don’t have a winged- or star-head for finger tightening to make life easier with repeated setting up, but there isn’t room beside the mount to allow that.

The bolt shown here is a make-shift arrangement and is not the proper bolt and washer.

The same could be said for the Lat Locking Screws, since they have to be slackened off and re-tightened before and after setting up/Polar aligning. However, these could reasonably be replaced with hand operated bolts, rather than rely on the Allen key, as there is ample room.

A note re. the tripod, is that it has an alloy top plate and I do wonder how resilient it will be to the repeated attachment of the mount. However, I also bought the Mini-Pier and the threads on this are inserts pressed into the alloy and look to be made of a more bolt friendly material. I plan to leave the Mini-Pier on the tripod.

Tracking

As I said I don’t guide so I can’t offer any figures. So the best I can do is provide some subs from my recent tests. You’ll need to bear with me on this as I’ve not many examples to date. My first examples are of M3 showing different sub durations of 90s, 120s and 150s. Unfortunately I was having trouble with my optical train and have got out of shape stars towards the edges anyway so that may confuse. Here they are for what they are worth:

90s

120s

150s.

 

My second offering is a sub from an attempt at M81 shot at 90 seconds:

 

The full image is posted here https://stargazerslounge.com/topic/352345-m81-m82-with-gem45-unguided/.

In summary then:

Pros

• The iPolar is a doddle to use, though does need a laptop to be set up for the alignment process, but that can be put away afterwards. Far better than kneeling on the floor and craning one’s neck.

• I’ve found tracking to be good enough for me up to about 1½ minutes, though possibly beyond that to 2 minutes or more, without guiding, with a FL of ~560mm and load between 6-7kg. Depends on how purist one wants to be about ‘round stars’.

• It’s quiet whilst tracking but slewing is by no means silent. I’m always concerned about disturbing neighbours so perhaps I’m being unduly critical. It’s quite difficult to judge how loud these things are in the middle of the night when you are standing next to the source. Then again, I’ve not used other mounts to compare it with.

• The hand controller seems fairly logical to use.

• Assuming I’m setting up everything correctly, I’ve found that the homing in on alignment stars to be somewhat ‘out’, and have always needed a significant correction to align. I do a 3-star align and I find this to be the case for each star. However, when I come to align on my target I found that it centred the object very well. May be I have significant cone error which will only be corrected for after the 3^rd align, if I understand correctly.

Cons

• The need to reset the altitude setting to around 40° in order to replace it into the case.

• Fiddly washers beneath the mounting bolts which are easy to lose. A touch of grease might help them to be retained by the bolt.

• Having to use the Allen key on the Lat Locking Screws.

• When aligning, the stars offered are in magnitude order, which from one point of view is logical, but is a bit of a pain when one wants to find particular stars. It would be good to be able to change your preference on star order.

That's it for now, and I hope that it's been of some use.

Ian

Edited April 19, 2020 by The Admiral

[MarkAR]

Good write up, awaiting the next instalment.

[Ricardo70]

On 19/04/2020 at 21:35, The Admiral said:

• Fiddly washers beneath the mounting bolts which are easy to lose. A touch of grease might help them to be retained by the bolt.

• Having to use the Allen key on the Lat Locking Screws

Great initial write up Ian, there always seems to be some flaw in design that could be made better, in any mechanics.

A suggestion for fiddly washers, would flanged bolts be ideal?

A suggestion for the lat locking screws, would screws that have a deeper head to incorporate incremental holes, on the grippy bit where a metal rod/pin can be inserted to tighten them up, help?

Just a couple of ideas, that’s all. Obviously you will know best having it right in front of you.

Richard

[The Admiral]

40 minutes ago, Autoglassman said:

A suggestion for fiddly washers, would flanged bolts be ideal?

I don't think so as the washers are the same diameter as the head. I think their purpose must be to allow some slippage so that the mount can be adjusted for Az against the pin.

42 minutes ago, Autoglassman said:

A suggestion for the lat locking screws, would screws that have a deeper head to incorporate incremental holes, on the grippy bit where a metal rod/pin can be inserted to tighten them up, help?

I'm not quite sure I follow, but using the Allen key of itself isn't really a problem, it's just that for operations which have to be repeated each time the rig is set up it would be less fidly and more convenient if they could be tightened by hand. You always run the risk of dropping the Allen key in the garden too! All the more so as in order to put the mount back in its case they have to be slackened off again so as to allow the altitude setting to be reduced to ~40°. Note that these bolts have a shaped shank, they are not straight bolts.

You are right about minor flaws though, if they can be called flaws. Perhaps I am just being picky. But thanks for the suggestions anyway.

Ian

[Davey-T]

Seems a step backwards my old iEQ45 has proper knobs that tighten by hand with Allen key centres to tweak them up, on altitude and azimuth the only problem was when tightening the dec adjustment it shifted Polaris so I fitted shims in the gaps between the castings.

Hand controller is annoying as it doesn't scroll if I hold the button down so have to keep pressing and letting  go and pressing etc etc.

Dave

[The Admiral]

25 minutes ago, Davey-T said:

Hand controller is annoying as it doesn't scroll if I hold the button down so have to keep pressing and letting  go and pressing

I don't have any problem on that score.

Ian

[Ricardo70]

1 hour ago, The Admiral said:

it's just that for operations which have to be repeated each time the rig is set up it would be less fidly and more convenient if they could be tightened by hand.

Sorry, I misread the context, yes I can see how that would be a pain each time.

1 hour ago, The Admiral said:

I don't think so as the washers are the same diameter as the head. I think their purpose must be to allow some slippage so that the mount can be adjusted for Az against the pin.

Yes, you are quite right, they look like nylon/plastic washers? As you say, to allow necessary adjustment for polar aligning the mount

[GTom]

I am undecided which mount to use for a transportable c9.25 setup. The gem45 is the top candidate ATM, but considering the AZ-EQ5 and the CEM40 as well.

Have you gathered more AP experience with the mount since?

[CCD-Freak]

The largest scope I have put on my GEM45 has been a C8 with all the guide scope and other imaging stuff.  The guiding was quite good even at 2000mm. 

I don't know how much more your C9.25 weighs but I would think it would probably manage it just fine.