Me vs. the Astro-Physics 1200GTO

Weighing in at 95lbs without counterweights, and with an instrument capacity of 140lbs, periodic error guaranteed to be under 5 arcseconds peak-to-peak before correction and a price tag that would buy a new Citroen C1, the Astro-Physics 1200GTO is rivaled only by the Paramount ME as the 'ultimate' amateur mount. I've had a 'love it and hate it' experience with my Losmandy G11, and when the chance came for a mount upgrade I looked at a number of options. The Losmandy HGM Titan, Takahashi NJP and Mountain Instruments MI250 were all strong contenders, offering improvements in quality, capacity and accuracy over the G11, while the Astro-Physics 900GTO has the quality of the 1200GTO in a smaller, slightly cheaper package. The MI250 was particularly attractive; the company has a great reputation for quality and customer service, and the mount was significantly cheaper than the Astro-Physics mounts. But I'm looking long-term with this purchase - the mount should give me a decade or two of trouble-free service - and, in the end, decided to go with the best. The Paramount was just too expensive in the UK and, rarely, the 1200GTO was available without a waiting list, so I gave Astro-Physics a call and paid my 50% deposit...

August 2007: Ordering and waiting...

The mount is ordered and delivery is scheduled for October, although which bit of October isn't clear yet. As well as the mount itself, i've also ordered the following:

DOVELM2: I already have two Losmandy DAP5s to mount my Astro-Physics 130EDT on my G11, so rather than replace those I went for Astro-Physics' Losmandy-style dovetail for the 1200GTO.
1200SPA: the standard pier adapter for the 1200GTO. This will bolt on to the pier in my observatory.
M9404-A: 14" x 1.875" diameter Counterweight Shaft. I'm not going to be putting a lot of weight on the mount, so this short counterweight shaft will save a bit of space in the observatory.
2x 18SCWT: Two 18lb stainless steel counterweights for the mount.

In total that adds $748 to the bill. Ouch...! And, for now, there's not much to do but wait.

30th August 2007: Did I say October?

I got an email from Astro-Physics saying the mount is nearing completion and should ship in two to three weeks. Looks like it should be here before the end of September.

The 1200SPA pier adapter is already on its way, so I can get it drilled to match the observatory pier.

28th September 2007: In transit

5 packages are inbound from Machesney Park, Illinois - total weight is an impressive 168.5 pounds. UPS's online tracking service is proving remarkably addictive (Rockford, Il -> Addison, Il -> Hodgkins, In -> Louisville, Ky -> Newark, NJ -> East Midlands Airport so far). UPS relieved me of a couple of months' overtime on behalf of UK customs (and, I suspect, a large 'handling fee' for their trouble), and it should be here on monday. So the original 'October' delivery date was right. Just.

And a link that'll come in useful in due course: Roland Christen on autoguiding a 1200GTO

1st October 2007: It's here...

Five boxes arrived, as expected.

The quality of the contents is amazing. Everything is superbly machined and put together, and no expense has been spared on the componentry. All together it's an engineering masterpiece, with superb attention to detail. I knew to expect something special, but not quite like this.

The hand controller deserves special mention; very rugged, with a big, clear four-line display. Very different from the G11's "1980s" controller. The mount also came setup for 51N; nice touch.

Getting the mount setup in the observatory was straightforward, and, although I followed the instructions to the letter, it was obvious how everything fitted together. None of the pieces were impossibly heavy, so this could be a portable mount; however, it's better suited to a permanent home. Although it's impressively large, it doesn't occupy too much space and there's plenty of room left in the observatory. Once it was all setup it was time to roll back the roof of the observatory for a picture. Nothing but cloud in the sky, of course.

Finally, after spending so much time with PEMPro on the G11, I couldn't resist firing it up. Astro-Physics pre-programs the mount with periodic error correction, so I downloaded that. Looks pretty good:

3rd October 2007: "First GOTO:

The weather was fairly poor, but stars were visible through the murk so I could go about getting the mount polar aligned. The 1200GTO's pointing is fairly primitive compared to the G11, as it implicitly assumes that polar alignment is perfect and the OTA is orthogonal with the mount (the G11 can measure and compensate for errors in both). I didn't worry about non-orthogonality, but accurate polar alignment is very important for good GOTO performance.

Fortunately PEMPro v2 has a good polar alignment wizard that rapidly reduced my initial misalignment (three or four degrees!) to a level where I was only getting an arcsecond or so of drift per minute - not perfect, but good enough for now. Then my first challenge: finding a star to synchronize on. The 1200GTO works off accurate polar alignment and then a one-star synchronize to tell the mount where it is pointing, so the synchronization step is vital - unlike Gemini, where the pointing gets refined over a number of 'additional aligns', this is it. At 1040mm focal length - and with no finder 'scope - positively identifying a bright star was hard. I eventually found Schedar (Alpha Cassiopeiae) and synchronized. A GOTO from Schedar to M103 was spot on (although, as it was only 8 degrees, that's not the most challenging of tests).

As I had PEMPro up and running, I turned on PEC and collected a few cycles of data. The results were astounding. There were still tracking errors due to the polar misalignment and random effects of the seeing, but the periodic components had been almost totally eliminated - all that's left is 0.4" peak-to-peak.

As the power spectrum shows, there are no significant components, it's almost all random noise, mostly due to the seeing. The mount's performing flawlessly.

All in all the performance of the mount was wonderful. The handset is superb, and mount slews are impressive - the mount heads off at high speed, and just when it seems sure to overshoot, coasts briefly before stopping dead. The settle time after a slew seemed virtually zero. Integration with TheSky 6 and PEMPro worked very well, with none of the quirks that I saw with Gemini - with the 1200GTO the mount ends up where you clicked, rather than 'somewhere close'. Looks to be a great system.

Next time out I need to really investigate the GOTO performance to see if there's any reason to consider something like TPoint to recreate Gemini's pointing error correction. I also need to look into just what TheSky can do because I think I'm hardly scratching the surface so far, and tweak the polar alignment to get it spot on. But it looks really good so far, and - most importantly - it looks like it'll "just work" and I can forget all about the mount and concentrate on other things. I'm really hoping that these notes don't have to hit five pages...

4th October: polar alignment

Restarting from park-2 put Altair on the top-centre of my Atik 16HR (i.e. about 11 arcminutes out), so clearly my polar alignment efforts from last night were OK but not brilliant. Still, I synchronized and figured that the autoguider could probably deal with the misalignment, so I put the ST-402ME on my piggybacked FS-60C and hit calibrate in CCDSoft. That completed successfully, with stars slewing as expected. I could also move the mount using the "N/S/E/W" buttons in the guide window, so CCDSoft was talking to the mount correctly. I started guiding, and took a ten-minute exposure of NGC 7635 (the Bubble Nebula). Much to my surprise, stars were trailing ... a lot. In fact, it looked like the image wasn't guided at all, and the stars had just drifted over the ten minutes due to the polar misalignment. Hmm...

After recalibrating for longer and checking that CCDSoft really could move the mount (it could) I couldn't figure out what had happened, so decided to do my research the next day and move on to fixing up my polar misalignment. A recommendation on Cloudy Nights prompted my to download PoleAlignMax, and it turned out to be a revelation. It uses CCDSoft and TheSky to take an image and 'plate solves' to figure out where the telescope is actually pointing. After that it slews to two other locations and, each time, takes a new image and 'plate solves' again. Finally, it then uses the differences between where the telescope was told to go and where it actually went to calculate the polar misalignment. All that is totally automatic; once it's done it shows the errors in altitude and azimuth and you then just adjust the mount and repeat. Very easy indeed.

At first I had problems; PoleAlignMax couldn't talk to CCDSoft. Then, I discovered, neither could PEMPro. Although PEMPro could connect to AstroArt without problems, any attempt to connect to PEMPro gave me an obscure error:

Failed to connect to Camera: Library not registered. (Exception from HRESULT:0x8002801D (TYPE_E_LIBNOTREGISTERED)

Some work with Google suggested that this was due to a missing ccdsoft.tlb file, possibly due to it having been blocked by antivirus software. I turned of AVG and tried reinstalling from the CD that came with my ST-402ME, but didn't fix things. I then tried applying the latest update from Bisque's website did (oddly this appears to be the same version that was on the CD, v. 5.00.182). However, after that the .tlb file was there and things worked perfectly with both PEMPro and PoleAlignMax.

PoleAlignMax worked brilliantly, and made it effortless to reduce the misalignment from the initial five arcminutes that I got last night (which was what i'd typically accept with the G11) to under an arcminute. Goto at this point was very good, putting target objects close to the centre of the ST-402ME's small CCD. However, the real revelation of the evening was how brilliantly CCDSoft and TheSky can work together. TheSky's ImageLink routine can easily calculate position and image scale from a CCDSoft image, after which it's a few clicks to synchronize the mount's pointing. I'll be using this a lot more in the future. As a complete system the 1200GTO, TheSky and CCDSoft are far ahead of anything I've used before, so I'm looking at the Atik 16HR without much enthusiasm. It's a great CCD, but can't work within CCDSoft and so means doing without the TheSky integration.

After all that it was getting late, so I turned PEC on and shot a number of test images.

Not the greatest image - one unprocessed frame with no darks, at 100% resolution - but it shows how good the tracking is with this mount. Three minutes, unguided, with the 130EDT at f/8. The G11 could never have done that. This is a brilliant mount.

21st December: update

I've written very little about this mount (unlike the G11) because there's very little to write; it works flawlessly. Lack of a guide CCD meant that I spent the good weather of late October shooting unguided; three minute exposures at 1.5"/pixel turned out perfectly, time and time again. Longer exposures suffered from drift due to the slight polar misalignment, but three minutes unguided was fine - I had other things to work on. The November weather was awful, and I returned to autoguiding in mid-December when my SBIG ST-4000XCM arrived. This calibrates and guides perfectly, so I don't know what happened the first time I tried autoguiding. Right now it's perfect, and with 15s guide integrations the corrections are well under half a pixel at most.

My general routine with the mount is to wake it from 'park 2', slew to a bright star, take an image with the CCD, plate solve in TheSky and sync on the calculated position. Usually it's very slightly out, but synchronizing only takes a moment and after that GOTO is spot-on; the pointing accuracy is unbelievable, which makes multi-night imaging runs very simple indeed.

Apart from that there's not much to say. It just works. Undoubtedly the best money I ever spent in Astronomy.

That's all for now, folks!

Tune in tomorrow for the next exciting installment. But, for now, go back to the equipment page.