The iOptron GEM28 consists of a compact mount head that can rotate and tilt on two axes, and a lightweight 1.5” aluminum tripod with adjustable legs and a built-in bubble level. The mount head has a simple Vixen-style dovetail saddle, which we would highly recommend you replace with an aftermarket dual Losmandy/Vixen saddle from ADM so you can use either size dovetail plate.
The GEM28 uses stepper motors and belt drives to move the mount smoothly and quietly on both axes, with minimal backlash or periodic error. The mount can track at four different speeds (solar, lunar, sidereal, or custom), and can slew at up to 6 degrees per second. The mount also has a dual encoder mechanism that allows the user to manually point the telescope without losing alignment. Simply loosen the clutches and push the mount around, and the encoders keep track of where you’re pointed, even if you have been using the GoTo system. These same clutches are what you, of course, use to balance the mount.
The GEM28 requires polar alignment to achieve accurate tracking and GoTo pointing, as it follows the motion of the sky on an equatorial axis. A polar scope is built into the GEM28 to get you polar aligned. The mount also has a software polar alignment routine that can be performed using the hand controller or the iOptron Commander app, and is compatible with the iOptron iPolar polar alignment tool.
A single 4.5 kg (10 lb) counterweight is provided with the GEM28. This is enough for smaller payloads, but you’ll probably need more counterweights for heavier telescopes. The good news is that with a standard 20mm shaft diameter, the GEM28 accepts most counterweights for small to mid sized mounts, and a counterweight shaft extension is also available if you need it.
The GEM28 is usually offered with a lightweight aluminum tripod that can support the mount and the load of a telescope with some stability. The tripod has adjustable legs that can extend from 31 to 43 inches, and a built-in bubble level that helps with the initial leveling of the mount. The tripod also has an accessory tray that can hold the hand controller or other items. The tripod can be further extended by an optional 8-inch extension bar that can provide more height or clearance for larger and longer telescopes, such as long refractors.
The GEM28 is rather lightweight, at only 10 lbs for the mount head and 11 lbs for the tripod. This often makes for top-heavy setups. The stock tripod is fine for visual use, but with a very top-heavy rig (particularly the case with astrophotography), it can be a little wobbly. In addition to the light weight of the mount and tripod themselves, the tripod is also inherently unsteady because its legs are only 1.5” diameter, as opposed to the 1.75” and 2” legs normally used with mounts of this size and weight capacity rating. The beefier LiteRoc tripod is also available, and uses 2” legs, which are sturdier.
We would recommend a different, larger tripod or pier, such as the LiteRoc, for larger astrophotography setups over the stock 1.5” aluminum unit provided with the GEM28. The larger iOptron TriPier is also available for the GEM28.
The iOptron GEM28 features a GoTo system that can automatically point to over 200,000 objects in the sky, such as planets, stars, nebulae, galaxies, and more. The mount has a built-in GPS and WiFi module that can provide accurate time, location, and alignment data. The mount can be aligned using a polar finder, a polar scope, a polar alignment camera, or a polar alignment routine that can be performed using the hand controller or a smartphone app.
The mount can be controlled via the provided Go2Nova hand controller, a smartphone app, or a PC. The Go2Nova hand controller has a large LCD screen that displays the menu and information about the selected object. The hand controller also has buttons that can adjust the speed, direction, and mode of the mount, as well as access various functions and settings. It works well enough, but it’s not as intuitive as the controllers used by most other manufacturers. Thankfully, you don’t have to use it, as iOptron has made a dedicated smartphone app for their mounts that can connect to the GEM28’s onboard WiFi adapter. You can also control the mount via another app, such as SkySafari, or plug it directly into a PC.
The iOptron smartphone app, iOptron Commander, can be downloaded for free from the App Store or Google Play. The app can connect to the GEM28 mount via WiFi and provide a graphical interface for controlling the mount and selecting objects. SkySafari will also work independently of iOptron Commander to control the GEM28 wirelessly.
A PC can also be used to control the mount via ASCOM drivers that can be downloaded from the iOptron website. The PC can be connected to the mount via a serial cable or the GEM28’s built-in WiFi adapter. A PC can provide more options and features for controlling the mount and interfacing with other software, such as planetarium programs, imaging software, or autoguiding software. The GEM28 mount also has an autoguider port that can accept a standard ST-4 cable from an autoguiding camera.
The GEM28 is also available as an upgraded variant, the GEM28EC. The main improvement of the GEM28EC is that it features a built-in guide scope and guide camera that automatically guide the mount internally, though you can guide with an auxiliary guide camera and scope for even greater accuracy. Both versions are also available bundled with iOptron’s iPolar system for polar alignment, and are compatible with the iOptron iGuider Autoguider, which attaches to the side of the declination axis of the mount.
Using the iOptron GEM28 for Visual Observation
The iOptron GEM28 is a versatile and convenient mount for visual observation with a variety of telescopes. To use the mount for visual observation, you will need to attach a telescope to the mount with a dovetail bar. You will also need to level the mount and align it with the celestial pole, either using a polar scope, a polar alignment camera, or a software polar alignment routine.
For visual use, planetary imaging, and other non-critical applications, the manufacturer-specified 28 lb rating is the absolute maximum capacity of the GEM28. The LiteRoc tripod is arguably a bigger bottleneck than the mount itself, but either way, an 8” reflector, 6” refractor, or 9.25” Schmidt-Cassegrain is the biggest you can go with this mount.
The GEM28 is easy to set up and use for visual observation, as it is compact and lightweight, and does not require any counterweights or balancing. The mount also has a built-in GPS module that can provide accurate time, location, and alignment data rather than having to enter information yourself. The GEM28 includes various “quick align” options” that make it pretty easy to get set up for observing, and polar alignment is of course less critical for non-imaging applications. After alignment is completed, you can then select and automatically point the GEM28 to any object in the sky, or manually point the telescope by unlocking the GEM28’s clutches.
The iOptron GEM28 is a capable and user-friendly mount for astrophotography with a camera and a lens or a small to medium-sized telescope. To use the mount for astrophotography, you will need to attach a camera and a lens or a telescope to the mount, either using a Vixen or a Losmandy style dovetail bar. You will also need to level the mount and align it with the celestial pole, either using a polar finder, a polar scope, a polar alignment camera, or a polar alignment routine. You can then use the hand controller, a smartphone app, or a PC to select and GoTo any object in the sky, or manually point the camera or the telescope at your target.
The GEM28 can hold up to about 15-20 lbs for astrophotography purposes (the rule of thumb being that a mount can hold ⅓ to ⅔ of its weight rating for astrophotography). This corresponds to an 8” SCT or Ritchey-Chretien, 4” refractor, or a 6-8” Newtonian reflector. Larger telescopes will be unsteady and induce tracking errors in the mount. With autoguiding (a must for good images) and accurate polar alignment, the GEM28 tracks extremely well thanks to its stepper-driven belt drives, which should guide at well under 1 arc second in most situations.
Like most quality German equatorial mounts, the GEM28 is compatible with ASCOM drivers, and while you could use the hand controller or a smartphone/tablet app to control it for imaging, the best option is usually via a PC connected to the mount’s USB port or connected over WiFi. With a PC and automated image sequencing software, you can control your guiding, where your mount is pointed, automatically plate solve to find and center a target, and make adjustments to your motor focuser and filter wheel if you have one. If you’re operating the GEM28 in this manner, there is no need to perform a star alignment with an app or hand controller – just assemble, polar align, and let the software take care of the rest.
Should I buy a Used iOptron GEM28?
The iOptron GEM28 is relatively new, not the most popular product, and isn’t exactly widely available on the used market. However, if you can find a used GEM28 in good condition at a reasonable price, it may be worth considering. The good news is that this mount is fairly durable, and does not have many moving parts or complex electronics made out of cheap materials that can fail or wear out. However, you should check the condition and functionality of the mount before buying it if possible.
The iOptron GEM28 is a unique and innovative German equatorial mount that offers convenience, portability, and performance for amateur astronomers and astrophotographers. However, it may not suit everyone’s needs and preferences, and there are some other options within its price range that merit consideration.
- The Sky-Watcher HEQ5i Pro (also sold as the Orion Sirius EQ-G) is a classic and reliable German equatorial mount that can be used for both visual observation and astrophotography with small to medium-sized telescopes or cameras, up to 25 lbs or 15 lbs. for visual/imaging respectively. The HEQ5i Pro is similar in features, specs, and performance to the GEM28, but its interface is a bit simpler, more aftermarket accessories are available, and it features a sturdier 1.75” steel tripod by default.
- The Celestron Advanced VX is an affordable and proven equatorial mount, with a beefy 2” steel tripod and up to ~30 lbs weight capacity for non-critical applications. The Advanced VX is considerably inferior to the HEQ5i and GEM28, however, lacking WiFi operability by default, requiring the use of the hand controller to connect to a PC, and depending on low-quality servo motors for slewing/tracking.
- The iOptron CEM26 is pretty much identical to the GEM28 in features, performance, and capabilities but uses iOptron’s center-balanced design to improve stability at the cost of being a little more complex for new users to set up and balance properly.
- The Sky-Watcher EQM-35i Pro is a budget equatorial mount from Sky-Watcher, featuring a similar frame to the HEQ5i Pro and only slightly lowered weight capacity, along with stepper motors and the option of either a WiFi dongle (default) or hand controller for operation.
- The Sky-Watcher EQ6Ri Pro is a robust German equatorial mount that can be used for both visual observation and astrophotography with large telescopes. has a payload capacity of 44 pounds, making it suitable for large refractors, catadioptrics, or reflectors. It also features a GoTo system with a built-in database of over 42,000 objects, and like other Sky-Watcher mounts, it is available either with a WiFi dongle (controlled via the SynScan Pro app) or a SynScan V5 hand controller with a backlit LCD screen. The EQ6RI also features a built-in polar scope, and a belt drive system that reduces backlash and periodic error.
- The Sky-Watcher AZ-EQ6i, essentially an upgraded EQ6Ri Pro, has all of the EQ6Ri’s features with the added bonuses of Sky-Watcher FreedomFind encoders (allowing you to aim the mount manually by unlocking the clutches as in the GEM28), and the ability to be used in alt-azimuth mode. In its alt-azimuth configuration, the AZ-EQ6i can also hold a second, smaller telescope on the end of the mount’s counterweight shaft.
- The Sky-Watcher AZ-EQ5i, like the AZ-EQ6i, is a hybrid mount that can be used as either an alt-azimuth mount or an equatorial mount, depending on the user’s preference and purpose. It can be used for both visual observation and astrophotography with medium-sized telescopes or cameras, and features a similar weight capacity rating to the HEQ5/HEQ5i Pro. The AZ-EQ5i also has a dual encoder system (Sky-Watcher FreedomFind) that allows manual pointing without losing alignment.
- The Orion Atlas EQ-G (also known as the Sky-Watcher NEQ6) is a predecessor to the EQ6Ri, with many of the same features but no belt drives and usually controlled by a SynScan V5 controller.
- The Celestron CGEM II is similar to the Advanced VX but features a beefier mount head similar to the EQ6Ri or Orion Atlas. However, it lacks these mounts’ software compatibility, stepper motors or even a polar scope provided by default, making it only really useful for non-imaging applications.
Aftermarket Accessory Recommendations
In addition to the guide camera/scope which are a must for using the GEM28 for astrophotography with any telescope, you may want to invest in the iOptron iPolar for your GEM28. This tool is similar to the QHY PoleMaster and dramatically speeds up polar alignment if you’re unfamiliar with the process. As mentioned earlier, ADM’s dual saddle for iOptron’s GEM28 mount is a must, both for its more solid connection with your telescooe’s dovetail bar and also for the Losmandy D-style dovetail plate compatibility it offers.
Of course, you’ll also need a power supply for the GEM28, such as the Celestron PowerTank Lithium or a generic equivalent such as from Westinghouse. An AC adapter will also do the trick, but even if you have access to an outlet at your main location for observing/imaging the flexibility of a portable battery is nice to have. iOptron does offer a hard carrying case for the GEM28, but we would recommend just coming up with your own solution as it’s quite expensive and won’t accommodate bulky addons like extra counterweights or a battery.