Telescope Reviews: Mach1 GTO First Light (long!)

Mach1 GTO First Light Report

Background:
I have been an active visual astronomer for over fifteen years and an astrophotographer for roughly two years. For the past year and a half I have been using a Losmandy GM-8 for my astrophotography along with either an 80mm apochromatic refractor or a 110mm APO. While I found the Losmandy GM-8 met my needs well for visual use, I constantly struggled with the mount when using it for astrophotography. Right from the first I knew the GM-8 wouldn’t be my be-all and end-all solution for photography, so I put myself on the notification list for Astro-Physics’ new Mach1 GTO mount. Two weeks ago, the mount finally arrived.

Requirements:
In order to choose the right mount you need to be clear in your requirements. All mounts represent a compromise with regard to portability, cost, stability, weight, and load capacity. In choosing my new mount, here is the list of requirements I came up with:

Mount must be portable such that it could be easily transported and setup in the field by a single person.
No single piece of the mount could weight more than forty pounds—there are thirty stairs from my front door down to my driveway, and too much weight would discourage me from taking the scope out.
Scope, camera, and mount (including tripod or pier) needed to be able to fit inside my two seat car (passenger seat OK)
Mount needed to be able to comfortably handle an imaging load of at least thirty-five pounds. This would allow for the use of my current optical tubes with a little room to “grow” into a mid sized reflector or catadioptric
Smoooooth (and preferably low) periodic error
Go-to capabilities—I’ve become lazy over the last few years and prefer to spend my time observing or photographing rather than staring at star charts and star hopping
Equatorial design rather than computerized alt-az since long exposure astrophotography would be one of the primary uses for the mount
Budget was less no more than $8,000 for the mount, pier or tripod, and all required accessories—quite generous by most people’s standards

Mounts considered:

Astro-Physics Mach1 GTO
Losmandy G-11
Celestron CGE
Takahashi EM-200

I eventually ruled out the Celestron CGE because at the time Celestron was having some QC issues with the mount. I was also concerned that the tripod wouldn’t fit in my car. I ruled out the Losmandy G-11 because I wasn’t satisfied with the design of the drive system including the worm mounting blocks, oldham couplers, and the amount of backlash required to enable smooth tracking. I had already struggled with these issues in my GM-8 and didn’t want to continue with those struggles in a larger mount. I ruled out the Takahashi simply because I wanted to have go-to functionality without the need for a computer when using the mount visually. That left the Mach1 GTO as the last competitor, so I put myself on the notification list and waited for my name to come up. It took roughly 18 months for the mount to arrive—patience is definitely required.

First Impressions:
Astro-Physics was extremely helpful during the ordering process providing clear communications as to expected delivery dates, recommended accessories, shipment tracking numbers, etc. I purchased the Mach1 GTO with the following options:

Larger diameter (shorter length) counterweight shaft that stores inside the mount’s declination housing
Polar axis scope
‘Eagle’ portable pier
Fifteen pounds of counterweights
Accessory tray and bracket

Everything arrived well packaged in a single shipment of four cardboard boxes with no obvious signs of damage. Assembly and usage instructions were clear, accurate, and thorough for an experienced observer. I had no problems getting the mount assembled or figuring out its operation. Beginners not familiar with some of the basic concepts of polar alignment, celestial coordinate systems, etc. would probably have more difficulty, but that is not the intended market for this product.

I was impressed with the apparent quality and attention to detail that had gone into the design and manufacture of the mount. Counterweights were lined with brass sleeves and pins so as not to mar the counterweight shaft. Cables were of a heavy gauge with sturdy connectors. Internal routing of cables—including camera cables not directly associated with the mount—was well thought out to avoid snagging while slewing. Machining was of extremely high quality with no ‘rough’ angles or corners. Perhaps most impressive of all was the fact that Astro-Physics had been able to design and build a 28 pound mount capable of carrying a 45 pound imaging load--that's quite an accomplishment.

The hand controller, while somewhat large and clunky looking, is extremely practical in actual use. The display is easy to read (except during daytime conditions), provides good tactile feedback, has buttons large enough to be used with heavy gloves, and, according to the Astro-Physics specifications page, is responsive in temperatures down to -40C. The menu structure is well thought out and is a dramatic improvement on the Gemini controller I am used to. A minimum number of button punches is required to get to all of the most frequently used functions.
The Eagle portable pier is truly a work of art. It is much more stable than a traditional tripod of similar weight, yet it folds up small enough to fit inside the trunk of my two-seat car. You get all the stability of a pier without the time consuming assembly and disassembly.

One little niggle. I purchased an accessory tray and two-level bracket to go with the pier, and depending on how high the pier is set and how far the legs are spread, the accessory tray may have to be mounted quite low to the ground. It still keeps things out of the dirt, but it is less convenient than one might expect.

First Light:
For some bizarre reason, the weather gods chose to cooperate and the amount arrived one day before a new-moon Saturday with the forecast showing nothing but clear skies and good seeing. I had been invited to a small star party in Sonoma, CA and decided to take the mount and scope there for first light. My target of choice was M101—the pinwheel galaxy. I managed to get the mount setup in about fifteen minutes and waited for twilight to arrive.

Polar alignment was accomplished using the optional alignment scope. Astro-Physics purchases their polar scopes from Losmandy, so if you have any experience with that polar scope you will know what to expect. In general, the Takahashi polar scopes have the best reputation in the industry, but I have never had any trouble getting an accurate alignment using the Losmandy scope (I had one in my GM-8 as well). In fact, if you are willing to shim the polar scope a little bit with tape, an extremely accurate and repeatable polar alignment is possible with nothing but the scope. I’m sure it’s not up to the level of a good drift alignment, but I can easily manage an alignment that shows no field rotation in fifteen minute subexposures.

After polar alignment I chose to sync up my mount using a simple one-star alignment. I manually pointed the scope at a bright star near my intended imaging target, selected that bright star from a list of objects in the hand controller menu, and performed a ‘sync’. I then asked the mount to slew to my intended imaging target and took a test exposure to see if it was properly framed on the imaging chip. My subject was spot-on, dead center. We’ve all come to expect good pointing accuracy in our go-to systems, and the Mach1 GTO does not disappoint. Even after performing a meridian flip later in the evening, the Mach1 GTO was capable of easily centering objects on the large imaging chip.

Now it was time for the real test. Even after more than a year of tinkering with my Losmandy GM-8 and playing with guide settings I was unable to achieve really good tracking results. Apparently, a 22-pound imaging load is just too much for it. Often, I would need to throw out several subexposures due to football shaped stars—especially if there was any wind at all. And that’s with autoguiding. Even when everything worked well I felt like I was not getting all of the resolution the scope was capable of. The software I use for guiding—Equinox Image—reports RMS tracking errors between guide exposures, and with the GM-8 I was typically getting values in the 1.5 pixel range. That means that on average the centroid of my guide star was shifting 1.5 pixels every second. That translates into a shift of 3.2 arc seconds! Some of that, of course, is due to seeing conditions, but I always felt that much of it was due to a lack of smoothness in the mount’s tracking. What sort of RMS errors would the Mach1 GTO report? Let’s just say that the improvement was not at all subtle. Insteady of 1.5 pixel RMS errors, I got numbers averaging 0.08 pixels. That’s right—almost a 20 fold improvement in tracking versus the GM-8, and the seeing, while good, was far from exceptional. During moments of really steady seeing the software reported RMS values as low as 0.01! Finally, I felt like my mount wasn’t keeping me from getting all the resolution my scope and camera were capable of.

Here is a 100% crop of my first light image of the Pinwheel Galaxy. Sixty minutes of luminance data captured in Equinox Image and calibrated in MaximDL. Post processing consisted of some curves and levels adjustments as well as some basic noise reduction. No sharpening of any kind has been applied. Each pixel represents 2.6 arc seconds of sky.

Just to provide some context, here is the full frame image (or very nearly)

Second light with the Mach1 GTO provided an even harsher test—wind. Last Saturday I loaded the scope, camera, and mount into the car and drove to Mt. Tamalpais for an imaging session. Normally, I wouldn’t have chosen to take pictures with a first quarter moon, especially not during the spring when galaxies are the objects of choice, but I wanted to continue to work out any issues with the new mount. But there was a problem. Wind. From my observing location, I would estimate winds of seven knots gusting to fifteen. Hopeless, right? A 110mm refractor isn’t exactly large, but that’s more than just a light breeze. I decided to give it a try anyway just for the practice. I plugged the mount in and selected my imaging location. The keyboard froze. Uh oh. What was going on? I unplugged the mount and tried it again with the exact same result. I checked all the connections on all the cables to make sure everything was tight then unplugged the mount and tried it again. This time it worked perfectly. This problem has not occurred since. My suspicion is that the power cord was not making a good connection, and that the voltage dropped when the mount turned on the right ascension motor causing the controller to freeze. If I find the cause later, I will update this review.

Let’s cut to the chase. How did the mount perform? Slewing was accurate, and tracking was very good. I didn’t get the same incredibly low RMS numbers from my first imaging session, but I was still seeing results that were better than I had ever achieved with the Losmandy GM-8. RMS error was typically around 0.2 pixels which corresponds to 0.65 arc seconds of ‘shift’ per second. Good enough to get some pretty sharp images. Frankly, I suspect that the mount was almost completely unaffected by the wind, and that the slight tracking inaccuracies were due to the relatively poor seeing conditions.

Here is a 100% crop of the Whale Galaxy from the second light imaging run:

Visual Use:
With my particular scope, this mount is really overkill for visual use. In fact, even its predecessor, the Losmandy GM-8, was overkill. If you don't plan on astrophotography and need a mount that can handle 20 or 25 pounds for visual use I would probably stick with something like a Celestron AS-GT or maybe an Orion Sirius. If you need a little more carrying capacity, the Orion Atlas is a good choice. Where this mount really shines is in astrophotographic situations where the utmost in tracking precision is required. That being said, the mount obviously performs well visually. Slews were accurate across the sky, even when changing from one side of the meridian to the other. It's just overkill for most visual uses.

Summary:
If you are looking for a portable GEM for imaging with light to moderate loads, and aren’t bothered by the high cost or the long wait, the Mach1 GTO represents the current state of the art and is easily worthy of the Astro-Physics name. Mounts may be the least glamorous portion of an imaging system, but they are also the most critical. And this mount coupled with the exceptional Eagle portable pier does exactly what it is supposed to—it plays the ‘supporting’ role perfectly allowing the main characters to really shine.

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- Jared Willson

TMB 152 f/8 Apochromat
Fluorostar FLT-110 w/ TEC optics
Stellarvue SV80S
Astro-Physics Mach1 GTO
Takahashi Teegul SP Mount
STL-11000