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Astrotrac 360 tracking platform – first impression
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Astrotrac 360 tracking platform – first impression
by Magnar Fjørtoft
My Astrotrac 360 setup. Wedge and drive on a Berlebach Report wooden tripod, a large Manfrotto ball head, Sony A7rIII with 100-400 mm zoom lens, and battery pack strapped to a tripod leg, or in an insulated box on very cold nghts. The polar finder will rotate with the drive, so it is easy to find a comfortable position when aligning the tracker to the celestial north pole. A highly portable package.
After some waiting my Astrotrac 360 arrived, and the drive looks great straight out of the box. Beautifully machined, light weight, and compact. Just what I was asking for, after moving to a city, leaving my fully equipped small observatory behind me at the countryside.
The Astrotrac 360 comes as a modular and highly precise lightweight equatorial assembly with counterweight and RA and dec operation, and the mount can be autoguided. This review is limited to the Astrotrac 360 tracking platform, though, consisting of a single tracking module. My goal is to go as compact as possible, with no counterweights or other parts that add weight and bulk.
After I said goodbye to my Losmandy G11 equatorial mount, the autoguided Takahashi FSQ 106 apo refractor, an eight inches Vixen VC200L reflector, a couple of SBIG cooled CCD cameras, everything run by a computer, I felt the need for something very portable. I was looking for something more precise than my first generation Astrotrac TT320X tracking platform. I like this tracker a lot and use it for astrophotography with wide angle and short telephoto lenses. For longer focal lengths than about 100 mm, I find it a bit limiting, due to lack of tracking precision.
When I started my search for a precise tracking platform that could be easily carried around, the Astrotrac 360 was newly introduced. Promised tracking precision was within five arch seconds over fifteen minutes, which should be better than needed for excellent non-guided wide field deep sky astrophotography within my range of focal lengths, up to about 400 mm. I went for an early preorder, and a longer wait than expected.
When I finally got my 360 tracker, there was one question that needed to be answered as fast as possible: Can this drive replace much of my previous stationary equipment for wide deep sky astrophotography with short focal lengths, and also simplify everything?
My Astrotrac 360 with wedge is mounted on a Berlebach Report wooden tripod, with a 12-volt 3Ah scooter battery strapped to a tripod leg to ensure plenty of power during long and cold nights. Note that low voltage will cause the drive to stop, so be sure to keep the battery in an insulated box on cold nights if you are using a led or gel battery.
On very cold nights the battery is put into an insulated box, since this tracker seems to be pretty rigid on voltage level. On top of the tracker, I mounted a heavy Manfrotto ball head, sturdy enough to carry 400 mm focal length with a full frame mirrorless camera. This telephoto lens will soon be replaced with a 76 mm f:4.5 apo-refractor, with about 340 mm focal length and 6 x 4 degrees field of view.
Since the small apo-refractor has not arrived yet, I had to do the first tracking tests with my 100-400 mm f:4.5-5.6 tele lens, zoomed to the long end. This lens is very sharp, with high contrast, but suffers from coma toward the corners, so expecting pin-point stars over the full field is out of question. Still, this lens is capable of some nice deep sky photography.
After putting together everything, also the lens and camera, I noticed that the weight is well within what I find acceptable for moving around in the dark, sometimes away from my car. So far, so good.
When living on the northwestern coast of Norway, with high cloud percentage and plenty of rainy days, and snow during the winter season, buying new astronomy gear means trouble. Happened this time too. I had to wait until next year to test the gear. Luckily, I received the tracker in December and got clear skies the second day in January. An attempt the evening before failed, since clouds covered Polaris and the surrounding sky, keeping me away from any polar alignment.
The clutch on the drive unit has a large handle that operates silk smooth and is accessible no matter the position of the drive. All knobs on the wedge can be operated with gloves. Important when you have to fine-tune polar alignment in dark and cold environment.
This second day in the new year the close to full moon dominated a hazy sky, but not worse that I could do a coarse polar align and run some initial tracking tests. The first thing I noticed, was that the polar finder should be focused, both the scope and the setting circle, and then adjusted so that Polaris falls into the exact marking in the view. There are 3 screws for fine tuning the polar finder, and the process might be a bit time consuming the first times.
This night everything was a tad better, but far from perfect. The polar finder marking is lit by red diodes on the mount, so there is no need for batteries for the finder. Be sure to focus the polar finder and the markings before starting.
With high humidity and a lot of water vapor in the air, and temperatures below the freezing point, I could not even see the Milky Way. During the evening, hoarfrost caused my Astrotrac and my camera to be coated with ice. Eventually the battery gave up too, and I returned home. Now I was happy that the mount is easy to pack, with no small parts that is easily lost.
To fine tune the polar setting for astrophotography, I use the camera. All it takes is a few 2-3 minutes exposures. After a few night I felt comfortable with the adjustment procedure, and could use the camera screen to move the mount in the right direction to full end the polar alignment.
When set up properly, the drive can run all night without interruption. No need to start over again after about two hours, like previous generations of Astrotrac trackers, and with much higher precision than my TT320X tracking platform.
First real test shots
The third night got clear skies. I went to one of my dark favorite spots away from the city lights, but I had to hurry to get some deep sky exposures before the moon rise. The temperature was minus 16 to 18 degrees Celsius, about as cold as in a deep freezer. The Astrotrac 360 performed very well, with no signs of having trouble with the low temperatures.
At first, I set up the tripod so that the wedge was leveled. There is a very good spirit level on the wedge, making polar alignment easier. Then I adjusted the polar finder to match the surrounding constellations and placed Polaris according to the engravings. Five minutes test exposure, and no need to fine tune the polar alignment made the previous evening.
The Astrotrac 360 feels rock solid, and I had not a single missed tracked frame out of about 70-80 frames taken this evening, before the shine from the moon was too bright to continue. Exposure was two minutes for each sub frame. I did not use dark frames or flat frames.
When I moved from one deep sky object to another, I had to re-check my polar alignment, since the Berlebach Reporter tripod stood on snow and ice, and there is quite some friction when turning the ball head base, especially at such low temperatures. With the large knobs on the wedge, resetting the polar alignment was a joy, though, and done within seconds. Probably a heavier wooden tripod would be helpful for more sturdiness for my small scale astrophoto expeditions.
Flexibility is one of the devils when using trackers, wind is another. With the Astrotrac 360, I could not note any flexibility at all, so if the tripod and ball head is up to the task, this should be a very reliable setup. I have not yet tried the setup in wind, but my previous TT320X was sensitive to even a light breeze when using long focal lengths. The Astrotrac 360 seems to be noticeably more resistant to wind. Real world experience will answer this question.
This is my first impressions of the Astrotrac 360, and I might write a more in-depth review after using this fine tracker over a period, also with the awaited small and filed corrected apo refractor. A decent review should point out what is good and what is not so good, but after some nights with this new tracker, I have nothing negative to report other than the polar finder must be fine-tuned. Anyway, when doing unguided astrophotograpy, using the camera to check polar alignment is a more precise method, and recommended.
Worth the money?
In every discussion about star trackers, the price of the Astrotrac 360 comes up. Many will find this tracker to be fairly expensive, with a list price of about £ 1300, or US $ 1840. You also need a wedge to mount the tracker on the tripod, and an Omni Clamp to mount the ball head for the camera.
What do you get for the money? Build quality is excellent, and the tracker would most likely last for a lifetime. You also get high precision, noticeable better than with any other portable tracker on the marked. This means that guiding is not needed for those typical 2-4 minutes exposures I do with long telephoto lenses or short focal length apo refractors. Precision is up to what is promised.
This tracker seems to fulfill my expectations, bringing close to permanent mounted equatorial precision to a highly portable package. I have discussed the price of the Astrotrac 360 with mechanical engineers, and they ask me how this unit could be sold at such a modest price. My guess is that our judgement of price is relative, and so is request of or need for quality. Sturdiness and tracking precision also come at a cost, so if you do not want to trade up repeatedly, buying the Astrotrac 360 right away might even be an economical decision.
I find the cost acceptable, since I get a hazzle-free and trouble-free tracking that brings my astrophotography closer to the much more complex observatory setup I left behind.
Some Sample Images (click the image to launch a full-sized version):
Orion-nebula: Orion nebula and Running Man. One hour with 30 sub frames, each 2 minutes. Orion is low in the sky at my altitude. 400 mm and about 50% crop. All pictures are stacked with Registar and processed with Photoshop. No darks or flats were used.
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