iOptron GEM45, initial experiences

[Jerry Barnes]

I’ve had a GEM45 for a few weeks now and its had a few outings.  Generally I’m pleased with the mount but only just getting to know how to use it.

It looks well made and is nicely finished which is good as it wasn’t cheap.

If the legs aren’t extended then its footprint is a bit smaller than my EQM35.  It still feels perfectly stable though.

I haven’t tried to use the internal wiring to connect USB and power to the head as I think I need more power and USB3 not 2.  However I will have another look at that at some point, for now I’m keeping my cable in the same configuration I had before.

With the clutches dis-engaged the RA and Dec both move very freely, no friction I can detect.  In fact getting balance is tricky as its very sensitive.  As I have a focuser fitted the scope centre of gravity is off centre and in Dec it has a tendency to rotate till the scope is horizontal and the focuser at the bottom.  Its also very dependant on how much the cable weight is supported or not.

When first connected the mount seemed very picky about my USB setup.  A single USB connection links both the mount and the iPolar camera.  With that connected directly to my PC I could use iPolar but add in a hub or an extension lead and iPolar refused to connect.  That’s ok though as when I’m polar aligning I need to be beside the mount.  After that the mount connects to a 4 port hub and then via an extension lead to my docking station thingy (using a Surface Book).

The iOptron iPolar software is very easy to used and much easier than the polar scope, as it should be.  Fairly similar to Sharpcap which I used to use but doesn’t need the RA rotation as part of the process.  Sharpcap is there as a backup if I need it and is perhaps more responsive.  I don’t know which is more accurate, probably both are good for purpose.  Mechanically the adjustment of the mount to get the alignment is much smoother which helps a lot.  PHD2 is reporting better alignment than previously as well.

iOptron mount control isn’t as sophisticated as EQMOD but didn’t give any problems at first.  I’ve later had problems with meridian flip and initial investigation suggests its user error and not setting it up properly.  By default after the meridian is reached the mount stops tracking and throws an error if you ask it to flip (I think).  Either that or the pre-flip plate solve fails as the starts trail.  The advice seems to be set the mount to stop 5 mins after meridian and the controlling software to flip 2 mins after meridian.  Something like that anyway, next clear night will be a chance to check that all out.

I did get one occasion where plate solving just wouldn’t work and when eventually went outside to check the scope was pointing downwards not at the sky!  Again almost certainly my fault, possibly not setting the zero position before starting.  I think that was the time when I had to do the classic turn off and on (mount and PC) to get it all synched again.  Turning off just the mount or just the PC didn’t seem to work.

I’ve not tried to set up PEC but the documentation suggests its easy to do.  Given the clutches have to be disengaged before moving the axis manually I think once setup PEC will stay and the worm positions wont change unlike with EQMOD but I could have got that completely wrong.

Now to the important bit, does it track well?  Its certainly better than my old mount but it really ought to be.  There aren’t the random spikes I used to get.  I’m getting guiding error varying between 0.6” RMS and 1.3” RMS.  Monday night it was between .7” and .8”all night.  It seems to be target dependendent and likes to be a little east heavy.  I’m not convinced about that yet but need some more investigation and confirmation.  I’d prefer not to have to mess with the balance halfway through a session but if that’s what it takes…

More investigation and calibration to do.

All in all I’m reasonably happy with it, if I can reliably get guiding error to 1” or less I will be.  One of the reasons I chose the mount rather than the obvious EQ6R was the weight.  I can carry the GEM45 but would struggle with the EQ6R and at some point would like to take it away from the city and get to bortle 4 instead of 6.