In the world of astrophotography, there are several factors that must come together to produce a good image. Some variables we have no control of, such as atmospheric transparency or the weather. Others we do have control over, such as equipment and desire. With the advent of Digital SLR’s, the world of astrophotography has been opened to reasonably priced cameras that can serve a dual purpose of general daylight photography and astrophotography. The other part of the equation is a tracking mount to counter the movement of the earth and eliminate star trailing. The vast majority of the mounts first available to the DSLR astrophotographer were telescope mounts, and many simply mounted their DSLR cameras to their equatorially mounted telescopes, or had the cameras ride piggyback on the optical tube assembly (OTA). Many astrophotographers still do this, but the setup time is a limiting factor, as is the weight and bulk of all that equipment. What if you wanted to shoot the night sky quickly, with little muss or fuss? What if you wanted to do some wide field imaging, but did not want to drag out all of that gear just to track the sky? Well, the call for a solution to this dilemma was answered by several companies, but the one company I will address here is AstroTrac LTD... AstroTrac introduced the AstroTrac TT320, and they were at NEAF in 2007, where I met Richard Taylor. Richard was displaying and demonstrating his new tracking mount, and after a bit of chat, I decided to put a deposit down on one of the mounts and a polar scope. After waiting several months for AstroTrac to get the production going, they sent out the first mounts to the US, and I received mine in good order. To be honest, at first I didn’t know that the small package the deliveryman brought AstroPhoto Insight Magazine April 2008
was the mount. I though that it was another item I had ordered. I simply could not believe that the entire AstroTrac TT320 was in this small box. On first inspection, the mount seemed to be extremely well made. The parts were sturdy and well manufactured. Form and fit were excellent, and instilled confidence in how well it would perform. The small size of this mount, folded for storage, is amazing. It is 17.25 inches long, 3 inches wide, and 1.75 inches thick. It weighs in at exactly three pounds. The concept of this mount is simple, and I have learned that simple is often the best way to go. The pivot axis of the AstroTrac is the point of greatest support. Unlike German Equatorial Mounts (GEM) that place the weight outside of the tracking axis, this mount has all of the carried weight directly over the axis. This eliminates the need for counterbalancing. It is an incredible idea. Now I had to check out how and why it works. I took a bit of time to closely look at the drive system. All of the electro-mechanical gear is in the rotating worm drive assembly. The motor and control surfaces are in the lower parts of the drive assembly. The 12 volt power connector fits into a socket on the back of the motor
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drive. It is a standard 5.5mm barrel connector socket with a 2.1mm center pin. The connector is wired center positive. The front of the motor drive assembly has a large, clear etched polycarbonate cover for the drive’s worm gear. The cover is very attractive, as well as functional. The worm rod has an extremely fine pitch, but it is clearly well made, and well protected by the thick cover. The rest of the motor assembly is sturdy aluminum. The control surface is a small orange oval inset into the aluminum on the top of the motor drive case. There are four low profile surface switches for controlling the unit. With the unit rotated to the left, for Northern Hemisphere users, the buttons are, from left to right, LED brightness control, audible signal level control, motor rewind control, and the preset and start button. The center pivot of the mount has 2 arms that extend to the motor assembly. Both arms are made from sturdy ¼ inch aluminum. The outside edges of the arms are radiused to eliminate any sharp edges. The smoothed edges make the mount comfortable to hold when setting up, as well as pleasing in appearance. The lower arm is the base of the mount, and it is attached to the center pivot on the top, and the pivot point for the rotating motor assembly on the bottom. The upper arm is the arm that travels. It is attached to the pivot assembly on the top, and the worm gear rod on the bottom. For being a pivoting arm, it is amazingly stout. The center of the pivot point has a threaded inset on the bottom, and a short, threaded rod on the top. Both of these are threaded US Standard 3/8 inch, 16 threads per inch (TPI). The threaded rod on top takes the tripod head that you are going to use to hold the camera or telescope. All tripod heads that I am aware of will have this size socket in the base of the head. The threaded inset on the base is where you attach the mount to your tripod. If the tripod or head that you are using does not have the capability to use the 3/8 inch socket, you might want to think about a sturdier tripod and head. The photo industry has long used the ¼ inch, 20 TPI standards for light and mid weight applications and the 3/8 inch, 16 TPI standards for heavy duty applications. You can use a ¼-20 to 3/8-16 adapter to make it work, but if you plan on larger lenses and telescopes, I would recommend heavier duty equipment. I proceeded to set the unit up, per the 2 page instruction book that came with the mount. A quick read of the instructions allowed me to set up the mount, apply power, and start the initial run. I first wanted to see how long the mount would track before a reset. I started the stopwatch and mount at the same time and let them run. When the mount ran out of tracking rod travel, the stopwatch read 1 hour, 49 minutes, and 15 seconds. That was the time with the mount
AstroPhoto Insight Magazine April 2008
Figure 1: Head of the TT320 set to the northern hemisphere. Since I am the type of person who tries to catch an anomaly, I decided to switch the drive over to the southern hemisphere, just to see what happens. I pressed the rewind button and waited for the motor to rewind the pivot arm to center. I then rotated the worm drive assembly for the southern hemisphere, and started it back up. I should have known better, because 1 hour, 49 minutes and 15 seconds later, the mount reached its full travel. At least it is consistent. The mount also starts to beep during the last approximately ten minutes of travel, providing a nice reminder that the mount must be reset soon. I anxiously awaited a clear night to go out and try out the mount, and you all know how the skies get when you receive a new piece of gear. Well, the skies finally did clear up, and I took the mount up to my favorite observing site for first light with the new mount. I was using a heavy duty Bogen tripod and a 3-way Bogen head to hold the AstroTrac. I set the polar scope into place, used its onboard illumination, and aligned the mount. The AstroTrac polar scope was a breeze to use, using the northern and southern circumpolar asterisms to help you achieve a polar alignment. AstroTrac tells you that the polar alignment accuracy depends on the focal length you have decided to use. Although this is basically true, and wide angle views will show minimal trailing, I have found that the difference between a close polar alignment and an accurate polar alignment with this polar scope is only a couple of minutes. You might as well do it right. AstroTrac has the polar scope you need to start getting great shots, I recommend that you take the little extra time to do an accurate alignment. It is worth it, every time. I must also recommend that you have a tripod and head for the mount that allows controlled adjustments for polar alignment. The 3-way Bogen head just did not allow me to make the small
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adjustments to polar align the mount. The recommended Bogen Manfrotto 400 series geared heads will pay for itself in saved frustration in the long run, so go ahead and buy one when you buy the mount.
to come. I wanted to change my field of view for my next target. I needed a wider field that what the 300mm was giving me. I dismounted the 300mm lens, mounted my Sigma 105MM f2.8 Macro lens to the camera body, mounted the body to the mount For mounting your camera or telescope to the top of the and started shooting again. The difference in AstroTrac TT320, you will need another tripod head unit. I weight between the 300mm and 105mm lenses is selected the Bogen Manfrotto 488 Ball Head for my use. I large, but I did not need to make any adjustment to chose this head because of its good load bearing capabilthe mount. No counterweight issues at all. It does ity. The Bogen Manfrotto 488 will hold 18 pounds, just shy not matter because the weight is over the axis. This of the load rating for the mount of 22 pounds. I figured it is a HUGE benefit in my book. I spent the evening was a good match, but when you are using heavier equipshooting, not fussing with the mount. When the ment, you must be aware of slippage of any ball head. Ofmount was nearing the end of the travel, I would ten this slippage will happen slowly, over time, and ruin a stop shooting, rewind the mount, and start shooting couple hours of imaging. I speak from experience. again. After getting the hang of the mount, I would set up my shooting so that I would complete an Once everything was set up, and I had the mount polar imaging run before I had to rewind the mount. aligned, I hit the start button to preset the mount for trackSince that first night, I have used this mount many ing. Once the mount is preset, you must remember to hit times. As a matter of fact, since I got this mount, I the button again to start tracking. The plastic cover flashes have not been out to my observing site for astrogreen to let you know that the mount is tracking. This is a photography without it. It is so compact, so lightnice touch, and although I was a bit concerned about the weight, so easy to set up and use, that I keep it choice of green for this feature, it is not a problem for me, with me all the time. I continue to test the limits of at least not at our dark site. The LED’s for the control butthis mount. Taking image exposures of up to three tons are red, so no problems there either. The mount minutes is a piece of cake for this mount, and expomakes only the slightest whir when tracking, and a muffled sure times of up to ten minutes are possible with an whine when rewinding. This should not disturb even the accurate polar alignment. I recently was using the most noise sensitive of your fellow sky watchers. It is at this mount in some light winds, and the results were time that you can mount a small telescope with a reticle less than satisfactory. I had the mount set up on eyepiece on the TT320 if you another tripod that I own. It was wish to fine tune your polar alignlighter and did not have the ment. You can drift align this Manfrotto geared head. I initially mount like any other mount, and if thought that the large motor you plan on photographing a drive assembly was acting like higher power, narrow field of a wing and trying to lift in the view, this will probably get you wind. After checking several better results. Although not necpossible causes for the imaging essary, it is an option. errors, I wanted to assess the possibility that the mount design I placed my Sigma 300MM f2.8 was acting like a wing. I went lens on the 488 ball mount, and out one night onto a mountain mounted one of my Canon 30D’s ridge. The winds were about to the lens, added the Canon 20MPH, gusting to over TC80-N3 to control exposures, 35MPH. I set up the mount on a and started to shoot. After shootMeade LX200 tripod, and used ing a short series of exposures, I the base of a custom German noticed several things. First, my equatorial mount to mount the focus was off by a hair, though no AstroTrac TT320. This is much fault of the mount, and second, more solid that what I was prethe mount tracked like a charm. viously using. I put the mount The slightly out of focus stars into operation, and installed a were perfectly round, out of focus, 2X teleconverter to the 300mm stars. As I moved the camera f2.8 lens onto my Canon 30D. I from target to target, I got great then aimed, focused, and results every time from the started shooting images of a Figure 2: Full view of the TT320 mount. But the best part was yet globular cluster. The camera
AstroPhoto Insight Magazine April 2008
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Figure 3: Shot of the area around Deneb, including the North American Nebula and Pelican Nebula, using ten 3 minute exposures and a Canon 30D Camera with a 200mm f4 Olympus Zuiko Lens, shot at f4 kept shooting as the wind buffeted me and the AstroTrac. A quick check on the camera LCD showed me that the AstroTrac handled the wind just fine. The problem was the lighter weight tripod and head that I had decided to try that evening. Just like any other astrophotography setup, the more solid the tripod and mount for the imager, the better your chances for a great image. Do not skimp on the base for this mount. Use a good set of tripod legs and a good head for the mount. It makes a big difference. I have to say that this has been one of the best purchases I have ever made in my quest to photograph astronomical images. It has opened up many opportunities to do astrophotography when I might not have the time to set up a larger mount. Several evenings had a 1 or 2 hour window that I was able to set up and shoot in. I would not have been able to do that with any other mount that I know of. The AstroTrac TT320 is not the answer to all your needs. It is limited by its 22 pound weight limit, and any long telescope would be difficult to handle on this mount. However, if you want to use your DSLR’s and lenses to do wide field imaging, I can’t think
AstroPhoto Insight Magazine April 2008
of a better way to do it. You could also use a smaller SCT, Maksutov, or Short Tube Refractor with a small CCD camera on this mount as well. This mount is not limited to use with DSLR’s. The biggest possible downside to this mount is the fact that after almost 2 hours of imaging, if you want to continue imaging that object, you must reset the mount, reacquire and reframe your target, and start shooting again. I do not see that as a problem with this mount. First of all, most people shooting with DSLR’s are not shooting longer than 2 hours on one object. Second, even if you use a GEM mount, you still have to deal with meridian flip, so I can’t really see having to reset the TT320 as a major issue. I highly recommend this mount to anyone who is looking for a top quality astrophotography mount. It is sturdy, works extremely well, is very portable, and is amazingly accurate. It is money well spent. Michael Overacker, professional photographer and member of the Roanoke Valley Astronomical Society, reviews astronomy equipment at Astronomy Reviews http://www.astronomyreviews.com
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