Tak EM200 first slews

[MartinB]

Just like the economy decides elections when it comes to imaging, "it's about the mount stupid". Well having tweaked and tweaked my Vixen GPDX and finally got to understand it's moods I decided to upgrade. The GPDX needs nursing along when auto guiding. I was wasting too much time under precious clear skies fiddling. Also the load capacity of 10kg is ok for my current kit but there isn't much in reserve. I wanted a mount that just worked, straight out of the box, that I didn't have to fret over, that was portable and very quick to set up.

The EM200 along with the Astro-Physics Mach1GTO are the most expensive of the medium sized mounts and it really is difficult to justify spending this sort of money. In the end I didn't have to - I just sold my Laser dinghy which I hated sailing! I went for the EM200 over the AP because of availability, UK dealer but most of all the wonderful polar alignment scope which I reckon will gain me at least 15 mins on every session.

The mount is beautifully engineered. The tripod is solid mahogony, adjustment is sacrificed for rigidity - perfect for imaging. It doesn't need to be flat which is a further time saving. You can set it up on a hillside if you want! The clamps are very solid and all movements are silky smooth. The mount fits to the tripod using a through bolt. When this is nice and secure the the azimuth adjustment knobs still turn the mount very easily allowing very accurate adjustment.

The very chunky and rigid tripod

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The polar scope is remarkable. The RA axis has a spirit level, you turn the RA until this is level. This ensures the polar scope is properly positioned (hence no need for the mount itself to be level). There is a longitude off set which is a one off adjustment unless you travel. The polar scope covers are screw on so nice and secure. Illumination of the scope can be adjusted by a small screw on the control box. There are 2 circular scales, one for the date and the other for the time. Simply rotate the reticle until the time lines up with the date. You then simply line up polaris between two lines matching it with the year (this scale goes up to 2030!). If done properly this gives an alignment within 2 arc minutes of the celestial pole. Plenty for normal imaging without the need for drift or software alignment. You would only need to adjust more finely at very long focal lengths. Adjustment of alt and azimuth is a doddle with the mount moving easily in alt and az with no jerkiness and no need to loosen and tighten the bolt fixing the mount to the tripod. The only thing I'm not keen on is that the altitude adjuster has just one screw which increases the altitude. The mount is prevented from moving the other way by a clamp and a friction pad. This appeared to work very well until it started moving during an imaging session. I have now learnt to make sure this clamp is fixed very tight after adjustment. Fortunately there is no movment of the mount when this is done. One surprising absence is a latitude scale, perhaps because it wouldn't be accurate if the scope wasn't level. Even so, it would be very helpful when attempting to use the mount for the first time.

Spirit level for setting orientation of polar alignment scope (protected in this picture by the screw on metal cap

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Altitude clamp and longitude offset scale

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The mount comes with two versions of the Temma goto - Temma and Temma junior. The junior version slews at a snail like x250 (more than 3 times slower than an EQ6). Having said that, it is £500 cheaper than standard Temma and was available for immediate delivery so I had that one and have spent the "saving " on a trutek motorised filter wheel. The mount has a dinky hand set, again beautifully made in a solid metal casing. This handset merely moves the scope at slow or fast speed and is used for positioning the mount. Although it will run off 12v slewing speed is slower still. It comes supplied with a 24V mains adapter so that saves having to get a couple of leisure batteries until I need to go to a remote location.

Neat little handset hanging from it's peg on the tripod

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There isn't a hand set for the goto! You have to use planetarium software. Sky 6 has it's own dedicated Temma driver but it works perfectly well with Starry night pro using the ascom driver. I can also operate it from my PDA using The Sky Pocket Edition using either a blue tooth or a cable connection. Getting to target is very easy. Work out the nearest easily identifiable star and manually swing the scope onto this star. Centre it in the scope and in the software then sync. Centre the target in the software and then slew to centre of screen. A doddle and very accurate. Slewing from Vega to NGC 7023 put the Iris bang in the centre of the chip. The scope makes a gentle, unobtrusive whining noise when slewing but is a little sedate.

Temma control box

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The first guiding calibration in Maxim was a bit nervy since any significant backlash is revealed. The first attempt was a disaster. I hadn't realized that the speed of movement continues to be determined by the speed setting on the little handset. Maxim was set to calibrate using 20 second movements and, with the handset left on the fast speed the scope was well on it's way back to Vega before I realized what was happening. I am going to make this mistake lots, I just know it. It does the same when guiding - a 0.1 pixel error is give an 10 pixel correction! When I finally did the calibration Maxim ran a 20 second move in RA then back again, then a 20 second move in dec and back again. A perfect right angle was traced and the guide star came back to the identical pixel co-ordinates it started from. I think that is pretty phenomenal, in fact I didn't think it was possible for a mount to have no apparent backlash.

My first guiding run I was working off a guidestar exposure of 2 seconds. Maxim was reporting an RMS tracking error of just 0.07 pixels in both axes :shock: :shock:. The error would occasionally creep up to 0.2 pixels. When I put on the tracking error graph in Maxim I was quite disappointed by the jaggedness of the line. It took me a while to realize that the scale was only 0.5 pixel max and that the movements weren't sufficient for Maxim to trigger a mount correction. The jaggedness of the graph was down to the seeing! The mount was putting in a correction around every 15 seconds. It would be quite possible to work with a guide star off a 10 second exposure.

With everything running smoothly I went inside for a coffee and some "quality family time" but on coming out again there had been a large movement of the target on the chip. Looking through the subs there had been a massive movement of the mount. I now realize that the altitude must have slipped. I hadn't tightened the clamp sufficiently. There continued to be more small movements which the guiding managed to pull back but polar alignment deteriorated.

The images that came out (other than the ones when the altitude slipped) showed perfectly round stars off 15 minute exposures. This was at a focal length of 770mm. I ran a 5 minute unguided exposure which produced this: -

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A close up of stars from the same image

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Wired up ready to go - the summer house is where my observatory could have gone!

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So, I'm thrilled with the mount (which is a relief after what I've spent). Fantastic build quality and it just works - no drama, no fiddling, nothing going wrong, no inexplicable behaviour. It just tracks and tracks and tracks. Feels a bit like cheating really!

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[Kaptain Klevtsov]

Sounds almost too good to be true. I hope you get lots of clear skies to play with now.

Kaptain Klevtsov

[legion48]

Pffiff! Who needs a dingy anyway!

[GordonCopestake]

Cracking mount Mart, is that a WO FLT 110 too? What happened to the ED120? Was the dinghy worth that much?!

[MartinB]

Yes it did cost more than the Laser dinghy Gordon. The FLT 110 belongs to Steve, I'm giving it a whirl for him to see how it performs especially for imaging. Will be writing a full review in the near future

[moondog]

The EM200 seems like a keeper then Martin !

Look forward to some images from this set up.

8)

MD

[Zeffer]

That looks amazing and the stars are perfect! I hope to do a similar review of the Sphinx soon, but you know

[MartinB]

Look forward to some images from this set up.

Have posted images of NGC 7023 and IC 1936 MD. Hope to get out tonight for more