iOptron CEM120EC Center Balanced GoTo Equatorial Mount Head with High-Precision Encoders and WiFi
Part Number: 7301
Observatory-Grade Performance for the Demanding Imager
When astrophotographers demand the highest level of tracking accuracy, payload capacity, and mechanical integrity—without stepping into the six-figure price range—they often find themselves looking toward the iOptron CEM120EC. This is not just a heavy-duty mount. It’s a precision-engineered platform designed to support your most ambitious imaging setups and observatory builds.
Combining iOptron’s patented Center-Balanced Equatorial Mount (CEM) design with integrated high-resolution RA encoders, real-time periodic error correction (RPEC), and a payload capacity of up to 115 pounds, the CEM120EC is built to satisfy the needs of advanced astrophotographers and institutional observatories alike. It brings together stability, innovation, and expandability in a mount that can operate both at a permanent pier and in the field.
Designed Around the Payload—Center-Balanced for Maximum Stability
At the heart of the CEM120EC lies iOptron’s revolutionary Center-Balanced Equatorial Mount architecture. Unlike traditional German equatorial designs that shift the payload weight off-axis, the CEM places the center of mass directly over the pier or tripod. This drastically reduces torque on the mount’s mechanical components, enhancing stability and improving guiding performance—especially critical for long focal length instruments or multi-accessory payloads.
With this design, the mount remains remarkably compact for its class, and the payload/mount weight ratio of 2:1 is one of the best in the industry.
Encoder-Based Tracking with Sub-Arcsecond Precision
The key upgrade that distinguishes the CEM120EC from the standard version is the inclusion of a high-resolution RA encoder system. This optical encoder enables real-time feedback on the mount’s movement, allowing for < 0.15 arcsecond RMS periodic error. Unlike mounts that rely solely on PEC curves or autoguiding corrections, the CEM120EC constantly monitors its own movement and applies internal corrections during tracking.
For imagers pushing ultra-fine pixel scales or working without a guide scope, this level of native precision is invaluable. RPEC means the system adapts on the fly, compensating for minor mechanical deviations without interrupting your imaging session.
Built to Handle Complexity—Physically and Logistically
The CEM120EC is capable of supporting up to 115 lbs. of payload—excluding counterweights. This opens the door to large Ritchey-Chrétien or CDK optical tubes, tandem scope setups, or fully equipped refractor imaging rigs with filter wheels, rotators, and cooling systems.
To manage all those devices, iOptron built in a comprehensive cable management system, including:
-
3x USB 3.0 ports for high-speed data transfer
-
2x 12V DC outputs (5A) for camera or dew control
-
2x 12V DC outputs (1A) for lighter accessories
-
ST4 autoguider port, AUX, LAN, RS232, and more
-
All routed through the mount’s body to minimize tangle, snags, and cable fatigue
The days of external power strips and dangling USB hubs are over—you can power and manage your entire imaging setup directly through the mount.
Software Flexibility, Global Connectivity
Whether you run your observatory from a desk or halfway across the world, the CEM120EC has you covered. The mount supports control via:
-
Built-in Wi-Fi for wireless operation through ASCOM or INDI drivers
-
LAN (Ethernet) for hardwired, observatory-grade connections
-
USB and serial ports for direct PC access
-
Go2Nova® 8407 V2 hand controller for traditional on-site use, featuring an intuitive 8-line LCD display and a database of over 212,000 celestial objects
With iOptron Commander software, the mount is fully compatible with applications like NINA, Sequence Generator Pro, TheSkyX, and SkySafari, offering a seamless experience whether you're using Windows, Mac, or mobile platforms.
A built-in 32-channel GPS automatically sets time and location, eliminating manual configuration in the field. The mount also supports automatic meridian flip, customizable park positions, and remembers its orientation even after a power cycle.
Mechanical Confidence—Crafted to Last
Every part of the CEM120EC is built with longevity in mind. The gear system consists of massive 216mm worm wheels on both RA and DEC, paired with zero-backlash 26mm worms, riding on 80mm axles and mounted inside 125mm steel bearings. Combined with the refined belt drive system, the result is whisper-quiet operation and minimal mechanical wear.
Precision-adjustable clutches make balancing and axis unlocking straightforward, while large diameter altitude and azimuth adjusters simplify polar alignment—even under heavy loads.
The mount head itself is all-metal construction, weighing 57 lbs (26 kg)—robust enough for observatory use, but still transportable by a single person if needed.
Included Equipment
-
iOptron CEM120EC Mount Head
-
Go2Nova® 8407 V2 Hand Controller
-
Two 10 kg (22 lb) Counterweights (limited-time extra included)
-
38mm x 540mm Stainless Steel Counterweight Shaft
-
Serial and Hand Controller Cables
Note: Pier or tripod is not included and must be purchased separately.
Technical Specifications
| Feature |
Specification |
| Mount Type |
Center-Balanced Equatorial Mount (CEM) |
| Max Payload |
115 lbs (52 kg), excluding counterweights |
| Mount Head Weight |
57 lbs (26 kg) |
| Periodic Error (RA) |
< 0.15 arcseconds RMS (encoder-based) |
| Encoder Resolution |
0.035 arcseconds |
| Worm Wheels |
Φ216mm, 360 teeth, both RA and DEC |
| Worm Axles |
Φ26mm |
| Main Axles |
Φ80mm Steel |
| Bearings |
Φ125mm |
| Counterweight Shaft |
Φ38.1 x 540 mm, Stainless Steel |
| Included Counterweights |
2 x 10 kg (22 lbs) |
| Saddle |
17.2" Losmandy D-style, spring-loaded |
| Motor Drive |
Stepper motor with 128 micro-steps |
| Slew Speed |
Max 4°/sec (960x) |
| Power Requirement |
12V DC, 5A |
| Power Consumption |
0.7A (tracking), 1.8A (slewing) |
| Ports |
RS232, USB, USB 3.0, LAN, WiFi, ST-4, AUX |
| Cable Outputs |
2 x 12V (5A), 2 x 12V (1A), 3 x USB3.0 |
| Latitude Adjustment |
0° to 68°, azimuth ±5° |
| Operating Temperature |
-10°C to +40°C |
| Polar Scope |
Optional iPolar electronic polarscope |
| GPS |
Integrated 32-channel |
| Warranty |
2 years on mount, 90 days on electronics |
Observing Tip
For imagers with ultra-fine pixel scales (under 1 arcsecond/pixel), the CEM120EC's high-resolution encoders allow for unguided imaging that rivals guided performance on lesser mounts. This is especially useful when imaging targets across the meridian or in tight imaging windows. If you're using adaptive optics or frequent meridian flips, the precise mechanical repeatability of the CEM120EC saves precious setup time and prevents mid-session drift.
Final Thoughts
The iOptron CEM120EC is a purpose-built mount for those who demand the most from their equipment—whether you’re managing an institutional observatory or a private imaging pier. With real-time error correction, massive payload support, intelligent cable routing, and complete remote access, it’s a professional-grade tool priced within reach of serious amateurs. In a world of compromise, this is the exception.
