There's something familiar about a German equatorial mount. The telescope sits on one side of the declination axis, counterweights hang from the other, and the whole assembly balances around the right ascension axis. Astronomers have been using this arrangement for generations because it works. The iOptron GEM45 keeps that traditional geometry but brings some very modern engineering to a design that has stood the test of time.
Consider its weight. The GEM45 mount head weighs only 17.5 pounds (7.9 kg), yet iOptron rates it to carry up to 45 pounds (20 kg) of telescope and accessories, excluding the counterweights. That's a payload-to-mount-weight ratio of approximately 2.5 to 1, an impressive figure for a conventional German equatorial mount. Much of that achievement comes from the CNC-machined construction and the engineering experience iOptron gained while developing its center-balanced CEM series. Unnecessary bulk has been removed without abandoning the familiar equatorial arrangement.
This 7620A-HC package includes the GEM45 mount head, its built-in iPolar electronic polar scope, GPS, Go2Nova computerized hand controller, and a protective hard carrying case. It does not include a tripod, pier, or counterweights. That makes it a particularly sensible choice for someone who already owns a compatible support or is putting together a more permanent backyard or observatory installation and wants to select the foundation separately.
A Traditional Equatorial with Modern Mechanics
The GEM45 uses 4.33" (110mm) diameter worm wheels with 216 teeth on both the right ascension and declination axes. Each wheel is driven by a 0.67" (17mm) brass worm through a synchronous belt transmission. The 1.77" (45mm) diameter steel axis shafts are supported by 2.68" (68mm) bearings, substantial mechanical components for a mount head weighing less than 18 pounds.
Why do those numbers matter? An equatorial mount must move a telescope at an extraordinarily slow and consistent rate to compensate for the Earth's rotation. The worm and wheel provide the gear reduction needed for that motion, while the large shafts and bearings support the telescope as its position changes during the night. The belt transmission transfers power from the stepper motors to the worm drives without the additional meshing gear stages used in some conventional mounts.
iOptron specifies periodic error of less than ±7.5 arcseconds over the GEM45's 400-second worm period. Periodic error is the small, repeating variation in tracking speed caused by imperfections in the worm and wheel. The mount includes Permanent Periodic Error Correction (PPEC), which allows you to train a correction for the predictable portion of that error and retain it for later observing sessions.
For demanding long-exposure astrophotography, I would still recommend autoguiding. The GEM45 has an ST-4-compatible autoguider connection and USB computer control, allowing a guide camera and compatible software to monitor a reference star and make small corrections while an exposure is being recorded. PPEC reduces a known source of mechanical tracking error, while guiding can respond to additional errors that occur during an actual imaging session.
The GEM45 also has large quick-lock gear engagement levers on both axes. These allow the telescope and counterweights to be balanced with the drives disengaged and then re-engaged for normal tracking and GoTo operation. The controls are large enough to operate while wearing gloves, something you'll appreciate when setting up on a cold winter evening. Always support the telescope and counterweight assembly when releasing the drives, since an unbalanced system can move unexpectedly.
Forty-Five Pounds of Capacity Without a Forty-Five-Pound Head
A mount that can support 45 pounds of equipment opens up a useful range of observing and imaging possibilities. A substantial apochromatic refractor, a compact Ritchey-Chrétien astrograph, or a Schmidt-Cassegrain with an appropriate camera and guiding arrangement can all be considered, provided the complete load falls within the mount's mechanical capabilities.
The payload rating is not the only number to consider, however. A long 6" refractor can create greater leverage and wind exposure than a compact telescope of similar weight. The length of the optical tube, the location of its center of gravity, the rigidity of the mounting arrangement, and the imaging focal length all affect how well the system performs.
For visual observing, the GEM45's carrying capacity makes it an attractive alternative to the smaller mounts often paired with medium-aperture telescopes. For astrophotography, it gives you room for a cooled camera, filter wheel, electronic focuser, and guiding equipment without necessarily having to move into a substantially heavier mount class.
And because the head itself weighs only 17.5 pounds, the GEM45 is still practical for someone who regularly transports equipment between home and a dark sky site. You can remove the telescope and counterweights, carry the head separately, and avoid lifting the entire assembled system at once.
Internal Cable Management
Anyone who has spent much time photographing the sky knows that the telescope is often surrounded by cables. There's power for the camera, a USB connection for image downloads, another cable for guiding, and perhaps still more wiring for an electronic focuser, filter wheel, and dew control equipment.
On a conventional equatorial mount, these cables can become troublesome as the telescope moves across the sky. A cable that hangs freely when the telescope points east may become stretched or snagged when the mount slews west or performs a meridian flip. In an unattended imaging sequence, that can bring an otherwise successful night to an abrupt end.
The GEM45 addresses part of this problem with a prewired cable-management system. Connections at the saddle end include USB 2.0, a 12V accessory power outlet rated for up to 3 amps, and an ST-4-compatible guiding connection. These are routed through the mount to the corresponding connections below, reducing the number of separate cables that need to hang between the moving telescope and stationary equipment.
The USB connection is a pass-through rather than a complete powered USB hub, so a system with several USB accessories may still need a separate hub or imaging computer. The mount also provides a path for additional user-installed cables, although their routing and clearance must be checked carefully.
Internal cable management doesn't make every cable disappear. It does, however, reduce one of the more irritating mechanical problems associated with a computerized imaging system. Fewer exposed cable loops mean fewer opportunities for a connection to catch on a tripod leg or become tangled during a slew.
iPolar Alignment, GPS, and Computerized GoTo
The GEM45 includes iOptron's iPolar electronic polar scope built into its right ascension axis. Instead of looking through a traditional optical finder and positioning Polaris on a reticle, iPolar uses a small camera to identify the star field near the celestial pole. Software running on a connected computer then shows you how to adjust the mount's altitude and azimuth controls to achieve polar alignment.
Polaris itself does not have to be visible for iPolar to work, provided the camera can see enough surrounding polar sky to identify the field. This can be especially helpful when setting up at an unfamiliar observing site where trees or buildings partially obstruct the northern horizon.
The GEM45 has an unusually broad latitude adjustment range of 14° to 68°, making it suitable for many observing locations well north or south of the latitudes commonly encountered in the continental United States. Observers in much of Canada, Alaska, and northern Europe will appreciate the ability to adjust the mount to the elevation of the celestial pole at their location.
A built-in 32-channel GPS system supplies location and time information automatically. That's a convenience when moving between observing sites, since you don't have to enter your coordinates manually every time you set up. The Go2Nova hand controller provides computerized GoTo operation with a database of more than 212,000 objects and an eight-line, 21-character LCD display. A built-in heater helps maintain the display's usefulness in cold conditions.
The GEM45 also provides automatic zero-position searching, allowing the mount to establish its reference position without requiring the user to position the telescope manually with the same precision each time. Once aligned, it can locate and track objects selected through the hand controller or compatible computer software.
Wi-Fi is not built into this version of the GEM45. Wireless mount control can be added with iOptron's optional iStarFi adapter if you prefer using a compatible phone, tablet, or computer application.
Meridian Tracking and Observatory Use
As a German equatorial mount follows an object across the sky, the telescope eventually approaches the meridian, the imaginary north-south line passing through the zenith. Continuing too far beyond that point can bring the telescope or its accessories dangerously close to the tripod or pier.
Many equatorial mounts handle this by requiring a meridian flip, moving the telescope to the opposite side of the mount so tracking can continue safely. The GEM45 allows the user to configure its meridian treatment, including stopping or tracking beyond the meridian by a selected amount up to 20 degrees before performing a flip.
That flexibility can be helpful when an exposure sequence is nearing completion. Instead of interrupting an exposure precisely as the object crosses the meridian, the mount may be able to continue tracking long enough to finish the sequence.
The important consideration is physical clearance. A telescope, camera, or accessory can collide with the support before reaching the mount's maximum permitted tracking angle. Always confirm the available clearance with your particular telescope and support before using an extended meridian-tracking setting, particularly when operating unattended.
For observers building a backyard installation, the GEM45's relatively light head, permanent periodic error correction, internal cable management, GPS, and meridian controls make it a capable foundation for a semi-permanent or observatory system. The actual tripod or pier must be selected separately with this package.
What Owners Say on Cloudy Nights
The GEM45 has generated considerable discussion on Cloudy Nights, particularly among astrophotographers who want the carrying capacity of a substantial equatorial mount without the weight of some traditionally built competitors.
One owner who moved from a heavier EQ6-R Pro described the GEM45's relatively low weight as a major advantage. He also found iPolar considerably easier to use than his previous polar alignment arrangement and reported good guiding results after becoming familiar with the mount.
Another GEM45 owner described the internal cable-routing capability as one of the reasons he chose the mount. By routing his imaging connections through the mount and organizing the remaining equipment around a power distribution system, he reduced the loose wiring surrounding the telescope. That is particularly valuable for someone operating an imaging system remotely or allowing it to run unattended.
Owners also make a useful distinction between the GEM45's generous carrying capacity and the need to handle its quick-lock drive system properly. As with other precision equatorial mounts, the axes should be controlled when disengaging the gears, particularly before the counterweight shaft and weights have been installed. Taking a little care during assembly prevents uncontrolled movement of the mount head.
The overall lesson from these discussions is familiar to anyone who has spent time working with computerized astronomy equipment. The GEM45 offers an attractive combination of portability, capacity, and electronic features, but understanding the mechanical arrangement and learning a consistent setup procedure are important parts of getting the most from it.
Under the Night Sky
A mount with 45 pounds of carrying capacity gives an observer considerable freedom in choosing an optical system. Pair the GEM45 with a substantial apochromatic refractor and a cooled astronomical camera, and the spring galaxy season becomes an excellent opportunity to explore objects that reward both image scale and long integration times.
M101, the Pinwheel Galaxy in Ursa Major, spreads its spiral arms across a surprisingly large region of sky. Under dark conditions, a well-matched telescope and camera can record the brighter star-forming regions scattered along those arms, including the knots of nebulosity that give the galaxy much of its photographic character.
NGC 891 in Andromeda offers a very different kind of galaxy photograph. Seen almost edge-on, it has a prominent dark dust lane crossing its luminous disk. The Triangulum Galaxy, M33, is another rewarding subject, particularly the enormous emission region NGC 604 embedded in one of its spiral arms.
For a more difficult challenge, IC 342 in Camelopardalis is a large, relatively faint spiral galaxy whose light is partially obscured by dust in our own Milky Way. It rewards patient imaging under transparent, dark skies, with enough total exposure time to separate its delicate spiral structure from the background.
Summer brings the rich nebular fields of Cygnus, including the Crescent Nebula, NGC 6888. Its curved shell of glowing gas is a particularly attractive narrowband imaging target, while the nearby star fields and extensive surrounding emission nebulosity provide opportunities for different focal lengths and compositions.
Of course, you don't have to use the GEM45 exclusively for astrophotography. A capable visual telescope on a properly supported equatorial mount can make an evening of lunar, planetary, double-star, and deep-sky observing particularly enjoyable. Accurate GoTo finds the objects, and automatic tracking keeps them in view while you examine fine detail or share the eyepiece with another observer.
Observing Tip: Balance the Entire Imaging System
When balancing a German equatorial mount, remember that the telescope is more than the optical tube alone. Cameras, filter wheels, focusers, guide scopes, dew heaters, and cables all contribute weight, and their positions can change the balance of the assembly.
Before balancing, assemble the equipment in the configuration you intend to use. Position the camera at its normal operating angle, attach the guide scope and other accessories, and arrange the cables so they have sufficient clearance throughout the mount's expected range of motion.
Follow iOptron's recommended sequence for balancing the declination and right ascension axes, keeping control of the telescope and counterweight assembly whenever the gear engagement levers are released. Use the telescope's position in the saddle to establish declination balance and the counterweight position to establish right ascension balance.
Once you've found the appropriate positions, small removable marks on the dovetail and counterweight shaft can make subsequent setups faster. This is especially useful if you routinely remove the equipment for transportation but use the same telescope and imaging accessories each time.
Before starting an unattended imaging session, slew the telescope through the positions it will encounter during the night and check cable clearance, counterweight clearance, and the configured meridian limits. A few minutes spent checking the physical arrangement can prevent a much more unpleasant surprise several hours later.
FAQ
- What else do I need to use the 7620A-HC?
- A compatible tripod or pier and appropriate counterweights for the GEM45's 28mm counterweight shaft. The mount head, shaft, hand controller, iPolar, GPS module, power adapter, and hard case are included.
- How does the GEM45 compare with the CEM40?
- The GEM45 uses a traditional German equatorial layout and has a 45-pound payload rating. The CEM40 uses iOptron's center-balanced arrangement and is rated for 40 pounds. Both are relatively lightweight, computerized equatorial mounts with features suited to visual observing and astrophotography. Telescope dimensions, support options, and personal preference for the mounting arrangement should influence the choice.
- Does the GEM45 need autoguiding for astrophotography?
- For demanding long-exposure imaging, autoguiding is recommended. The mount supports guiding through its ST-4 connection and compatible USB computer control. Permanent periodic error correction is also included.
- Does the GEM45 have built-in Wi-Fi?
- No. Wireless control is available through iOptron's optional iStarFi adapter. The mount includes USB computer connectivity as standard equipment.
- What is the difference between the GEM45 and GEM45EC?
- The GEM45EC adds a high-resolution right ascension encoder for real-time tracking correction. The standard GEM45 uses conventional worm-drive tracking with permanent periodic error correction and supports autoguiding. The EC version is intended for customers who want the additional tracking precision of an encoder-equipped mount.
Supplied Accessories
- iOptron GEM45 German equatorial mount head with 45 lb rated payload capacity
- Built-in iPolar electronic polar scope
- 6" dual Losmandy D / Vixen-style dovetail saddle
- Go2Nova computerized hand controller with heated eight-line display
- GEM45 GPS module
- 1.10" (28mm) diameter stainless steel counterweight shaft, 280mm long
- Aluminum hard carrying case for the mount head
- Two coiled mount control cables
- USB cable
- 100–240V AC power adapter
- Quick Start Guide
Tripod or pier and counterweights are not included with the 7620A-HC package.
Optional Accessories
iOptron 5 kg Counterweight (#8027): A counterweight designed for the GEM45's 28mm shaft. The number of weights required depends on the telescope and accessories being carried.
iOptron 2.5 kg Counterweight: Allows smaller adjustments in the total counterweight mass for different telescope arrangements.
iOptron Tri-Pier (#8034): A substantial freestanding pier-style support that may suit observers building a semi-permanent backyard or imaging system. Confirm the appropriate GEM45 mounting arrangement and hardware.
iOptron iStarFi Wi-Fi Adapter: Adds wireless mount communication for operation through compatible smartphone, tablet, or computer software.
Final Thoughts
The GEM45 is appealing because it delivers the familiar operation of a traditional German equatorial mount without the bulk that often accompanies a mount in this payload class. At 17.5 pounds, the head is relatively easy to handle, yet the 45-pound rated capacity provides useful room for a substantial telescope and the equipment needed for serious astrophotography.
I particularly like the combination of mechanical and practical features. The large worm wheels and bearings provide the foundation for accurate tracking, while iPolar, GPS, automatic zero-position searching, and internal cable management address some of the routine inconveniences associated with setting up a computerized equatorial mount. None of those conveniences replaces careful balancing and alignment, but together they can make the equipment more pleasant to use.
The head-only package will make the most sense to someone who already has a compatible tripod or pier, or who plans to select a support specifically for a permanent observing location. There's no reason to purchase another tripod if you already have an appropriate one, and the included hard case gives you a secure place to keep the mount when it isn't installed.
For someone who appreciates the traditional German equatorial arrangement but wants a lighter, more modern interpretation, the GEM45 is well worth considering. It has the carrying capacity for a serious observing or imaging system without making the mount head itself an unnecessarily difficult piece of equipment to live with.
