GM1000 HPS Review by Tony Cook

Tony Cook, 1 May, 2015

10 Micron GM1000 HPS Review

I have been a highly satisfied user of a 10 Micron GM1000 HPS mount for nearly two years. Prior to moving up to the 10Micron mount Iíd been happily using a Losmandy GM8 mount since 2004 with the Gemini mount controller and a Televue 85 apochromatic refractor.

My favourite astrophotography targets are comets, especially when they are aligned close to a spectacular deep sky object. Living near the edge of the Yorkshire Dales gives me access to relatively dark skies once you are well away from the big cities of Leeds, Bradford and York (meaning travelling more than 30 miles northwards!). However Pennine weather is fickle so Iíve developed a mobile astrophotography set up that is transported and powered from the back of my car. I have a series of favourite remotes sites spread from the Forest of Bowland in Lancashire across the Pennines to the North Yorkshire Moors. I also have a permanent pier site outside a trailer in a holiday park but parts of the sky there are not accessible due to high banks or light pollution so the mobile rig is still vital for me.

A few years ago I reviewed the ease and reliability of my mobile set up after a disastrous week in Devon where the limitations of my current set up became very apparent and I decided it was time to upgrade. It was during a visit to the Astrofest meeting in London (2013) that I had a chat with Ian King on his trade stand about my imaging needs, particularly as I was after an accurate mount that was quick and reliable to polar align in the field and could be used unguided for at least 6 minutes or more. He led me over to this elegant looking black mount made by 10Micron and told me that it would be an excellent solution as its unguided performance was superb due to its use of an absolute encoder system. After researching the mount and its absolute encoder capabilities over the next month I became convinced this was the mount I needed so I ordered one from Ian. My only worry was the level of portability Ė would it be too heavy?

So how did it work out? Did I make a good choice? Maybe the best place to start is my log book. What follows is one of the first sessions with the mount in August 2013. Iíd just had the concrete base for the permanent pier installed by the holiday park owner, so I was keen to learn how to polar align the mount. As I was familiar with the advanced polar alignment procedures offered by the Losmandy Gemini controller, I was pleased to find that the 10Micron mount had very similar procedures and was just as easy to use and much quicker to complete with pretty well guaranteed high accuracy:

ďSo the first run was to get used to the new mount, learn how to build the pointing model and nail polar alignment and report back how easy and how accurate the outcome was. Imaging runs come later once the concrete has fully cured and I've dealt with some shrinkage issues.

So after the GM1000 was set level on the pier (it has a bubble level) I booted the mount computer. After the boot completed, I set up the longitude, latitude and time by hand. Once setup, I selected from the hand-pad screen menu: Alignment -> 3-Star Align. The procedure starts by offering a limited list of preferred stars. I picked Altair, the GM1000 slews close and emits a beep when done, then itís over to you to center it in an illuminated reticule eyepiece and press "enter" when you are done (the keypad ď+Ē and ĒĖď keys are used to change the slew rates at any time the menu selection isn't active - this is a nice touch and very different from the Gemini - much easier in fact).

Next up - pick Deneb from the list ... slew, beep, center with the hand-pad and press "enter". My last star was Alpheratz.

At this stage you can use the hand-pad to get information on how good the pointing model is (as an RMS error value in arc seconds) and what your polar align error is in terms of offset distance (in arc seconds) and position angle or alternatively as Alt/Az off set from the true pole.

A 3-star align is just the start. The next step is to add more stars to the pointing model. From the keypad select 2-Star Refine and pick a star from the list, the GM1000 will slew to it, halt and beep when ready and you center the star in the reticule eyepiece and press enter. Keep doing this to build up say a 12 to 20 star model from stars spaced widely over the sky - you can build a max of 100 stars into your model which is more practical to do (time wise) in a permanent setup. After each additional star you are told what the RMS pointing error is.

Now is a good time to polar-align. Pick the Polar Align procedure from the keypad and pick a star from a list. I picked Altair as it was near the meridian and fairly close to the equator (the Gemini procedure I used before works best in this region of the sky Ė so I assumed this would be true for the GM1000 also). This time you must not use the hand-pad to center the star, but use the mount alt/az adjustment knobs to do the centering. Press enter when done. Thatís very nearly it - but not quite as the pointing model is now invalid after the physical mount adjustments.

Final step is to 3-star align and a series of 2-star refines once more to rebuild a full pointing model.

I experimented for 4 hours to learn how best to do it and how fast it could be done and how good the results are and if further model building and polar alignment iterations improved things. I performed the procedure 3 times from scratch with the pointing model wiped out at the start.

The optimum solution trading time for accuracy was to 3-star align, then add stars to build at least a 12 star model, polar align, then repeat the 3 star align a second time (I added a Barlow this time for centering) and again go for at least 12 all-over-the-sky stars and polar align a second time and finally finish off with a third 3 star align and12+ star refine to build a final model. This took less than 30 minutes as the mount slews fast. With practice model building and polar alignments could probably be reduced to 20 minutes.
The results of 3 runs:

RMS error of pointing model over whole sky: 5 (best) to 10 arc seconds (worse)

Error of polar alignment: 16, 17 and 18 arc second offset in the 3 runs I did (2 polar align iterations).

As an additional test I centered Altair (near equator) and Alkaid (high dec) on the crosshairs (12 mm eyepiece + x2 Barlow on 600mm FL scope) and noted that the star remained on the crosshairs for at least 20 minutes.

First impressions Ė the GM1000 setup, model building and polar align are extremely easy to do, very accurate with little effort and time and the observed tracking accuracy is superb.

I got this mount to avoid auto-guiding! Looks like it does what it says on the tin.Ē

The log book entry turns out to represent the repeatable ease experienced when polar aligning the mount, an important consideration for mobile imaging as well as for a more permanent setup. In fact Iím now practiced and can get polar alignment down to a reported 15 arc-seconds error within 20 minutes.

If any added star significantly degrades the model (the RMS suddenly gets much worse) you can delete it via the hand-pad and try another star. Typically you can accurately polar align within the twilight period and be ready for imaging when darkness sets in.

What else do I like about the mount and its controller? The scope balancing function is excellent. Iíve measured the balance points to within 0.2% for a variety of setups and the counterweight positions and scope balance position are marked on the counterweight shaft and the sides of the scopes so I donít have to run the procedure each time.

The controller is a small compact industrial embedded Linux box that comes in a padded soft case that you can hang off pier bolts or your tripod. This controller is sufficient to command all the functions of the mount without the need of a laptop. However you can control the mount with your laptop if you wish with the 10Micron supplied software or any ASCOM compliant program. The hand-pad is nicely designed for thickly gloved hands and is protected by a zipped soft cover with a clear front. The display is very easy to read.

The use of absolute encoders has major benefits other than providing its unguided tracking performance. The first is that you donít have to train out periodic error with a PEC function. The mount controller monitors the error in real time in a feedback loop and corrects itself. This works because the encoders are mounted on the main shaft which is directly attached to the scope. Second is if the clutches slip for whatever reason just ask the mount to return to the position you were imaging and it will do it without error (assuming your pointing model is built correctly!)

How did the mount work out for portability? This was my one concern and it was a slight problem at first as the mount is heavy but not entirely unmanageable. When you transport or handle the mount it is essential to release the clutches to prevent damage. This makes lifting the mount slightly awkward as parts unexpectedly rotate and shift. With a bit of practice you learn how to do this without risking a drop. I bought the optional carrying case so I can lift it easily in and out of the car boot and protect it from scratches.

The other essential item for mobile imaging is the GPS receiver for setting your geographic position and accurate time. The mount controller can also account for atmospheric refraction and this needs you to enter your altitude and the current atmospheric pressure.

The astrophotography results Iíve obtained over the last two years have been astounding. To date Iíve not dropped a sub-frame due to tracking errors Ė only to clouds or my own errors with snagging cables. Iíve regularly imaged using unguided 10 minute sub-frames without issue. Iíve not gone longer yet because of light pollution limitations but I know that it can track accurately at 600mm FL to over 20 minutes Ė I used a 12mm illuminated reticule eyepiece and Barlow to check this. My main scope has been a Televue 85 working at F6 but Iíve now started to use a corrected F3.6 10Ē ASA Newtonian astrograph which needs only about a third of the exposure time to match the F6 scope, so long tracking times are not a major concern with the bigger scope.

The astrograph is much heavier as it needs 3 x 6 kg counter weights compared to just a 6 kg one for the TV85, but the mount copes with this without effort. Iíve included photographs of the two set ups I use for mobile and static imaging (Figure 1 and Figure 2).

Of course the proof is in the pudding so Iíve also included some samples of my photographs taken on the GM1000 HPS over that last 2 years (2013 to 2015 Ė see Figure 3 to Figure 7; the camera is either a modified canon 450D or an unmodified canon 40D).

Other that the awkwardness of lifting the mount with clutches released there is not a lot I donít like about the mount. If I had to have a quibble there is an annoying inefficiency in the scope balancing procedure that starts each run on one specific side and proceeds to finish the other side. Instead of doing the next run in reverse it laboriously slews slowly back to the original start. Thatís it Ė one annoying feature Ė not bad really.
T
here is a lot more offered by the mount and its controller. For example it can be remotely controlled via a network cable for unattended operation. However this is something that Iím not likely to use for a long while. The controller has all the usual database items: planets; bright stars; catalogue stars; Messier objects; NGC objects etc. There are a variety of tracking modes for the moon, sun and sidereal rate as well as custom, closed loop and comet tracking modes. I havenít yet explored all the functions but one I want try out soon is the fast satellite tracking mode. I want to view the International Space Station passing over in real time Ė something the GM1000 can do with ease!*
Tony Cook (Leeds UK)

* You can watch the satellite tracking mode in action on YouTube including an impressive high speed meridian flip! - https://www.youtube.com/watch?v=GD_W3MAQ7eQ


Figure 1 My mobile rig uses a Losmandy tripod, a 10 Micron GM1000 HPS mount, controller box and hand-pad with a Televue 85 scope. A 10 Micron carrying case is used to protect the mount when packing it away in a car boot.


Figure 2 My permanent rig featuring the 10 Micron GM1000 HPS and an ASA N10 astrograph. This combination is well suited as the scope and camera weight is easily handled by the GM1000.