iOptron HEM27 Mount

StrainWave 17 Hybrid Drive: 480:1 Reduction and Zero Backlash

Every HEM27 pairs a high-torque StrainWave gear on the critical right ascension axis with a backlash-free worm/belt system on the declination axis. The StrainWave gear eliminates the traditional RA worm, delivering zero backlash and smooth, consistent tracking with a 360-second native period, while its 480:1 reduction ratio gives the stepper motor precise control. Putting harmonic-drive technology where tracking matters most, and a lighter system on DEC, is what keeps the mount so compact without compromising performance for imaging, visual or solar observing.

3.65 Payload-to-Weight Ratio: 29.74 lbs Capacity in an 8.15 lbs Body

The HEM27 head weighs only 8.15 lbs (3.7 kg) with its dual Vixen/Losmandy saddle, yet carries up to 29.74 lbs (13.5 kg) of telescope and camera without a counterweight or shaft. That turns a full imaging setup into a true grab-and-go kit that is fast to deploy and light enough for travel. When your system grows, adding the optional counterweight shaft and 10 lbs counterweight raises the total payload capacity to 44 lbs (20 kg).

EC Versions: High-Precision RA Encoder with Realtime PEC

The "EC" in HEM27EC stands for the high-precision encoder built into the RA drive. It provides constant, high-resolution feedback on the axis position, enabling Realtime Periodic Error Correction. Non-EC versions use traditional PEC, where the mount records its periodic error and plays the correction back; that works well, but it cannot account for non-repeating errors or instantaneous deviations.

• Smoother tracking: Realtime PEC corrects gear imperfections on the fly instead of replaying a recorded curve.
• Better data: Tighter star shapes and longer sub-exposures, especially under high-resolution imaging conditions.
• Less guiding effort: Reduced workload on your autoguider and more room for unguided exposures.

Choose Your HEM27 Version

All HEM27 versions share the same StrainWave 17 hybrid drive, 29.74 lbs counterweight-free payload, Go2Nova® 8409 controller and built-in Wi-Fi. They differ in tracking correction, polar alignment and latitude range. The HEM27 has no optical polar scope, so plan your polar alignment method when choosing.

• HEM27 Mount: The core hybrid mount with traditional recorded PEC. A great fit for autoguided imaging, visual and solar observing, or if you already have an electronic polar alignment solution.
• HEM27 Mount w/ iPolar: Adds iOptron's internal iPolar electronic polar scope for fast, screen-based polar alignment with ~30 arcsec precision from a Windows PC. The most straightforward path to precise polar alignment.
• HEM27EC Mount: Adds the high-precision RA encoder for Realtime PEC, for imagers who want the best tracking accuracy and already have their own polar alignment method.
• HEM27EC Mount w/ iPolar: The complete package: RA encoder with Realtime PEC plus the internal iPolar, for demanding long-exposure and high-resolution astrophotography.
• HEM27 Mount Low-Latitude (0-22°): A version of the HEM27 configured for observing sites at 0–22° latitude. The other versions adjust from 15º to 65º, so choose this one if you observe from a site below 15° latitude.

Go2Nova Control and Cable Management: 212,000 Objects, Wi-Fi and 2 x 12V Outputs

The Go2Nova® 8409 hand controller gives you GoTo access to approximately 212,000 celestial objects at slew speeds up to 6º/sec. Built-in Wi-Fi lets you command the mount from a smartphone, tablet or PC using iOptron Commander or ASCOM-compatible applications like N.I.N.A., TheSkyX or Sequence Generator Pro, with a USB port for wired control and an ST-4 compatible autoguide port. An integrated cable management system provides two 12V DC outputs (4A max) and a USB 2.0 port on the saddle plate to power cameras and dew heaters without snag-prone cables, and an electronic friction brake engages when power is cut to protect your equipment from unexpected movement.

iOptron HEM27 vs. GEM28: StrainWave vs. Traditional German Equatorial

The HEM27 represents a different design philosophy compared to iOptron's traditional center-balanced equatorial mounts like the GEM28.

• Counterweights: The GEM28 requires counterweights to balance any payload, adding weight and setup time. The HEM27 handles up to 29.74 lbs without any counterweights, making it faster to deploy and significantly lighter for travel.
• Backlash and Periodic Error: The GEM28 uses a worm-and-wheel system, which inherently has some backlash and periodic error that may require autoguiding to correct. The HEM27's StrainWave gear is backlash-free by design, and the EC versions add Realtime PEC on top.
• Polar Alignment: The GEM28 often includes an integrated optical polar scope, while the HEM27 has none. That is why the HEM27 is offered with the internal iPolar electronic polar scope, the recommended choice for precise astrophotography alignment.