The longer I am engaged in shooting astro-landscapes, the longer focal lengths I seem to use. Some 2 years ago, I started shooting “deepscapes,” landscape astrophotography with deep-sky objects dominating the background. That mercilessly revealed the limits of my little tracking mount. I found myself looking for a mobile astrophotography mount with the capability for deep space imaging at medium-high focal lengths and still fits into a backpack to be taken on a hike. After researching my options, the Sky-Watcher AZ-GTI turned out to be the perfect solution for my purpose.
Deepscape Mount Requirements
To be usable for deep space imaging, a mount has to meet a few requirements:
- Equatorial setup
- Two-axis control (RA & DEC)
- Computer controllability
- 2-axis guiding capability (RA & DEC)
- Enough load capacity to carry a deep-space imaging rig
I soon found that the selection of lightweight mounts that meet these requirements is rather limited.
Drive Mount Options
There are new harmonic drive mounts, like the Rainbow Astro RST135 or the HOBYM Crux 140 Traveller. But these would have required me to sell a kidney to pay their steep price of 3500$ or more, and I was not prepared to do that just yet.
The iOptron Smart EQ Pro+ mount fits the niche. But it seemed a rather old and bulky system and therefore did not look very appealing for my needs.
Finally, I found the Sky-Watcher AZ-GTI. I initially ruled it out, as it is an ALT/AZ mount and therefore not suitable for astrophotography. After reading several reports of imagers who had apparently modified the AZ-GTI to make it an equatorial mount, I decided to give it a try.
Meet the Sky-Watcher AZ-GTI
The Sky-Watcher AZ-GTI is a rather modern mount with built-in WiFi that can be controlled with Sky-Watcher’s Synscan app from any Android or iOS smart device. The size of the mount head is similar to Sky-Watcher’s well-known Star Adventurer tracking mount.
The Sky-Watcher AZ-GTI hompage describes it as follows:
- Multi-purpose alt-azimuth mount
- 11-pound payload capacity
- SynScan Go To telescope mount with 42,900 object+ database
- Built-in WiFi
- Controlled with SynScan Pro app for iOS and Android
- Freedom Find dual encoder technology
- DC operation (batteries not included)
Normally, the AZ-GTi comes with the mount head, pier extension, and tripod and sells for a very competitive price of 379$, which again puts it in the price range of the Staradventurer tracking mount.
As the provided tripod does not fold small enough for my purpose, I only bought the AZ-GTI head and the pier extension, saving me a few bucks. It does not seem, though, that this option is available from US sellers.
Modifying the AZ-GTI for Astrophotography
Unfortunately, the Sky-Watcher AZ-GTI is not sold in an astrophotography package. The reason for this escapes me, but it means that the mount needs some DIY tinkering to make it astrophotography-capable. This includes:
- Updating the motor firmware
- Mounting it on an equatorial wedge
- Add a Vixen-Style mounting plate
- Finding a counterweight solution
- Finding a way to polar align the mount
Updating Motor Firmware
Out of the box, the Sky-Watcher AZ-GTI is not able to be operated equatorially. First, you must update the motor firmware. The required firmware, as well as a Windows Motor Controller Firmware Loader, is available on the official Skywatcher webpage at http://skywatcher.com/download/software/motor-control-firmware/
Unfortunately, Sky-Watcher does not offer a solution to update the firmware from an Apple computer. Therefore you need access to a Windows PC.
Once the motor firmware is updated, the Synscan app asks you during every initialization whether the mount is operated in ALT/AZ or Equatorial mode.
Strangely, Sky-Watcher seems to try to shy its customers away from using the AZ-GTI for astrophotography. In the description of the firmware update, they placed a warning that astrophotography performance is not guaranteed. This is funny, as no mount can guarantee good astrophotography performance if you do not know what you are doing.
Mounting the AZ-GTI on an Equatorial Wedge
After updating the firmware, you need to mount the AZ-GTI on an equatorial wedge. Basically, the wedge from any tracking mount can be used for this. Both the iOptron and the shiny red William Optics wedge will work out of the box.
The Sky-Watcher Star Adventurer wedge, however, needs a small adjustment. The screw for the Vixen-style mounting bracket on the Star Adventurer wedge needs to be replaced because its handle is too wide and blocks the mount’s rotation. As the original screw has a standard M8 thread, you can simply use an inexpensive M8 screw for this purpose.
To enable me to lock the screw tightly without any tools, I chose a slightly different solution. I sawed off the head of an M8 screw and replacing it with a winged nut, countered with a regular nut. I get a nice handle that does not block the rotation of the mount.
Vixen-Style Mounting Plate
In any case, you will need a Vixen-style mounting plate that screws into the tripod thread of the AZ-GTI to attach the mount head to the wedge bracket. If, like me, you decide to buy the Star Adventurer wedge, you have the advantage that it comes with such a plate that perfectly fits the AZ-GTI and ensures that the plate cannot slip from the wedge or unscrew from the mount head.
Another thing worth noting is that the AZ-GTI sits on the wedge in the opposite way to a normal tracker. Instead of dialing in your latitude, you have to set the wedge to 90° minus your latitude. That’s no problem for the Sky-Watcher wedge, which covers a full 90° range of motion.
Depending on your latitude, it could pose a problem for wedges that cannot be adjusted over a 90° range, like the William Optics wedge for low latitudes. For the William Optics wedge for high latitudes, this is not a problem as its operational range of 32°-59° means that it is usable from latitudes 31°-58° with the AZ-GTI.
Finding a Counterweight Solution
A properly balanced mount is important for good tracking, and therefore, you need a counterweight bar for the AZ-GTI. The mount has an M12 thread for exactly this purpose. Strangely, Sky-Watcher does not offer any bar that fits.
You can find commercial solutions for this problem on eBay or AliExpress, but why spend 35-70$ for something you can build on your own using parts you can buy in any hardware store for a few bucks? All you need is a threaded M12 bar, three M12 nuts, a winged nut, a threaded spacer, and of course, a 1 kg counterweight with an appropriate 12mm drilling.
I cut my 1-meter threaded bar into two pieces of 40cm and 60cm. The shorter bar is perfect for balancing my rig with photo lenses, while the longer bar nicely balances the mount if I use my heavier telescope.
Finding a Way to Polar Align
The best mount is of no use if you cannot polar align it. Due to its native ALT/AZ design, the AZ-GTI has no polar scope. The Synscan app has a polar alignment routine that doesn’t require a polar scope, but it is not very accurate and it requires the use of a finder scope. I, therefore, do not recommend using the Synscan app for polar alignment.
Again, there are third party solutions available, like e.g. the polar scope adapter from Artesky.
While this certainly works, the best solution is probably using a computer for electronic polar alignment with plate solving technology, which brings us to computer control.
Computer Control for the Sky-Watcher AZ-GTI
While you can use the AZ-GTI as a standalone solution, a computer is needed to unleash the full potential of this little mount.
For exposures over 1-2 minutes with higher focal lengths, you will need autoguiding to avoid star trailing due to gear imprecisions. Furthermore, a computer gives you access plate solving software, which, as mentioned before, can be used for precise electronic polar alignment without a polar scope, for increasing GOTO accuracy, and to precisely frame your compositions.
While the built-in WiFi lets you connect some computers wirelessly to the mount, I found it much easier and more stable to use an EQDIR cable.
Portable Computer Options
Dragging a laptop computer into the field may not sound very tempting, and fortunately, there is no need for this. There are several Raspberry Pi-based solutions (e.g., ASIair, StellarMate, Astroberry) available that can control your entire rig.
The AZ-GTI can be internally powered by 8 AA batteries or via an external 12V connection.
As I require a 12V power supply for my cooled astro-camera and my ASIair mini-computer, I use the Celestron Power Tank Pro Lithium. It can supply my entire rig for at least 2 nights.
The AZ-GTI in Operation
How does the Sky-Watcher AZ-GTI perform in a real life environment? I’d say amazingly well.
Below is an example of a 2 minute guided exposure, taken at the 11-pound load limit of the mount. It has an equivalent full-frame focal length of 1000mm, using the 500mm telescope and the micro 4/3 astro-camera shown in the image above.
This example shows perfectly round stars in a 5 min guided exposure at 200mm equivalent full frame focal length:
Sky-Watcher AZ-GTI – A Perfect Choice for Deepscapers
These images prove that the AZ-GTI is a very capable mount for deep space imaging, and thanks to its small size and weight, it is the perfect choice for deepscapers who need to hike to their shooting spots to get that perfect alignment.
To explore more about Deepscape astro landscape photography, try these following articles:
- Sky-Watcher AZ-GTI: The Perfect Mount for Mobile Astrophotography? - March 11, 2021
- Going Deep – Pushing the Limits of Nightscape Photography - January 24, 2020
- Airborne Astrophotography - September 13, 2019