iOptron CEM40 Mount

A 2.28 Payload-to-Weight Ratio: 40 lb Capacity from a 17.4 lb Head

The core of the CEM40's design is its Center-Balanced Equatorial Mount architecture, which places the payload's center of gravity directly over the tripod's or pier's central axis. This increases stability and allows the mount to handle a 40 lb instrument load with a head weighing just 17.4 lbs, a ratio traditional German equatorial mounts struggle to match. The entire structure is CNC machined from metal and finished in anodized red/black, giving you a rigid, durable platform you can carry to a dark sky site without the burden of an excessively heavy mount.

Precision Drive: 216-Tooth Worm Wheels, PPEC or < 0.3 Arcsec RMS Encoder

Both axes use large Φ110mm worm wheels with 216 teeth, driven by Φ17mm brass worms through a synchronous belt transmission. The spring-loaded, zero-backlash worm system maintains constant gear pressure for responsive guiding corrections, while 1.8° stepper motors with 128x micro-stepping achieve a fine 0.08 arcsecond resolution.

• CEM40: A native periodic error of less than ±7.5 arcseconds, further improved with built-in Permanent Periodic Error Correction (PPEC), gives an autoguider very little work to do.
• CEM40EC: A high-resolution encoder on the Right Ascension axis drives Real-time PEC (RPEC), correcting worm gear error as it happens for a periodic error of less than 0.3 arcseconds RMS, precise enough for multi-minute unguided exposures with many short-to-medium focal length refractors.
• Solid Shafts: Both RA and DEC axes are built on Φ45mm steel shafts supported by Φ68mm bearings for maximum stability under load.

Go2Nova Controller: 212,000+ Objects, GPS and 4.5°/sec Slewing

The Go2Nova hand controller's 8-line, 21-character LCD is your command center for a database of more than 212,000 objects, and the built-in 32-channel GPS automatically enters your location, date and time for a faster, more accurate setup. Once aligned, the CEM40 slews between targets at up to 4.5° per second.

• Integrated Cable Management: Pass-through DC12V (3A), ST-4 and USB ports near the saddle keep camera and guide camera cables from snagging as the mount slews.
• Dual Saddle: The 6" dovetail saddle accepts both Losmandy D-style and Vixen V-style plates without adapters.
• Automatic Zero Search and Power-Down Memory: The mount finds its own zero position and remembers its state, giving you a reliable starting point every night.

iPolar Alignment: Accurate Setup from 0° to 60° Latitude

Every CEM40 eliminates the most tedious part of setup with its integrated iPolar electronic polar scope. Its sensitive camera and software plate-solve the star field around the celestial pole, so you achieve a precise polar alignment in minutes on your computer screen, without kneeling behind the mount and even when Polaris is obscured. The mount's wide 0° to 60° latitude adjustment range makes it a viable option for observers from the equator to high northern or southern latitudes.

Choose Your CEM40 Version

All versions share the same 40 lb payload, 17.4 lb head, integrated iPolar, GPS, Go2Nova controller and AC adapter. Choose the tracking model first, then the package that fits how you will support and transport the mount.

• CEM40 (standard): < ±7.5 arcsec periodic error with PPEC. Ideal for imagers who autoguide through the ST-4 port.
• CEM40EC: Adds a high-resolution RA encoder with RPEC for < 0.3 arcsec RMS periodic error, making unguided imaging with short-to-medium focal lengths practical and giving long focal length systems a steadier guiding platform.
• LiteRoc versions: Include the 1.75" stainless steel LiteRoc tripod (7 kg) and a 5 kg (11 lbs) counterweight, ready to set up and image.
• 1.5" Tripod versions: Include a 1.5" tripod in place of the LiteRoc, plus a 5 kg (11 lbs) counterweight, as a complete ready-to-use package.
• Case versions: Add a custom-fitted hard carrying case for transport and storage. CEM40 w/ iPolar & LiteRoc and CEM40 w/ iPolar & 1.5" Tripod do not include a case.
• iGuider version: Adds iOptron's iGuider guiding system to the CEM40 for autoguiding without a separate guide scope.
• NUC versions: Add provisions for mounting an Intel NUC mini PC on the mount (computer sold separately) for a compact, computer-controlled imaging rig with fewer loose cables.
• Head Only versions (CEM40 and CEM40EC): Mount head with iPolar, hand controller, AC adapter and hard case, with no tripod and no counterweight. The right choice if you already own a tripod or will install the mount on a pier.

CEM40 vs. GEM45: Choosing Your iOptron Mount

The CEM40 and its sibling, the GEM45, are two of the most capable mounts in their payload class. The choice between them often comes down to design preference and specific use cases.

• iOptron CEM40: With its 40 lb payload and 17.4 lb head weight, the CEM40's primary advantage is portability and ergonomics. The center-balanced form factor is inherently stable and easier to carry and set up, especially for observers at lower latitudes.
• iOptron GEM45: The GEM45 uses a traditional German Equatorial Mount design with a slightly higher 45 lb payload capacity. It can be a better fit for permanently mounted setups or for users accustomed to the workflow of a conventional GEM.

For most portable imagers, the CEM40's center-balanced design, lighter weight and excellent stability are a decisive advantage in the field.