The iOptron HEM27EC with iPolar combines the two upgrades that matter most to an imager on the HEM27 platform: a high-precision encoder on the right-ascension axis and a built-in electronic polar scope.
The mount head weighs just 8.15 lb (3.7 kg) with the saddle installed, yet iOptron rates it to carry 29.7 lb (13.5 kg) without a counterweight. The RA axis uses a strain-wave drive for high torque in a compact package, while declination uses iOptron's backlash-free worm-and-belt system. The EC version adds a high-precision RA encoder with Real-Time Periodic Error Correction, continuously reducing tracking error as the mount follows the sky.
The factory-installed iPolar handles the other side of the equation. Accurate polar alignment becomes especially important when you want the encoder to do as much of the tracking work as possible, and iPolar uses a camera and plate-solving software to show you how to adjust the mount toward the celestial pole without requiring Polaris itself to be visible.
For the portable imager, that is a compelling combination: encoder-assisted tracking, electronic polar alignment, nearly 30 pounds of counterweight-free capacity, and a mount head light enough to carry outside in one hand.
Features
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High-precision RA encoder with Real-Time PEC. The encoder continuously monitors right-ascension motion and lets the mount correct much of the strain-wave drive's tracking error internally.
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Built-in iPolar electronic polar scope. A factory-installed camera plate solves the polar-region star field and provides on-screen guidance for adjusting the mount's altitude and azimuth.
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Approximately 30-arcsecond polar-alignment precision. iOptron specifies maximum iPolar alignment precision at approximately 30 arcseconds.
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Polaris does not have to be visible. iPolar solves the surrounding polar-region star field rather than requiring Polaris or Sigma Octantis itself to appear in the image.
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29.7 lb counterweight-free payload. Carry up to 13.5 kg without a conventional counterweight shaft and stack of weights.
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Only 8.15 lb with the saddle installed. A payload-to-mount-weight ratio of approximately 3.65:1.
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Up to 44 lb with a counterweight. Add the optional shaft and counterweight when a heavier or more demanding telescope configuration calls for additional capacity.
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Hybrid drive system. Right ascension uses a 480:1 strain-wave drive while declination uses iOptron's backlash-free worm-and-belt system.
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360-second RA gear period. The high-precision encoder and Real-Time PEC work directly with the tracking behavior of the strain-wave RA drive.
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RA guiding filter. The mount can either accept external RA guide corrections or filter them and let the encoder handle RA while the guider continues correcting declination.
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Go2Nova 8409 hand controller included. Standalone GoTo operation with an approximately 212,000-object database and nine slew speeds up to 6° per second.
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Wi-Fi through the hand controller. The 8409 provides wireless connectivity for compatible applications such as iOptron Commander Lite and SkySafari.
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Integrated ST-4 autoguider port. Traditional autoguiding remains available in addition to software-based pulse guiding.
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Power and USB pass-through at the saddle. Two 12V outputs with a combined 4A maximum and USB 2.0 pass-through help keep camera and accessory cabling close to the telescope.
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Electronic friction brake. Designed to stop the mount safely during a planned or unexpected interruption in power.
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Automatic zero-position search. Built-in sensing allows the mount to locate its reference position electronically.
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Vixen/Losmandy-D convertible saddle. Accepts either dovetail standard, although changing between them requires reconfiguring the saddle hardware.
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Soft carrying case included. Appropriate for a mount built around portability.
What the Encoder Changes
Strain-wave gearing is what allows the HEM27 to carry several times its own weight without requiring a conventional counterweight system.
The tradeoff is that the tracking error of a strain-wave drive behaves differently from the comparatively smooth periodic error of a traditional worm gear. On a standard non-encoder strain-wave mount, the guider often has to make relatively frequent RA corrections to keep up with those changes.
The HEM27EC adds another layer of feedback. Its high-precision encoder continuously measures the RA axis and allows the mount to correct much of that tracking error in real time.
iOptron says the resulting accuracy is good enough that many users may choose to image without guiding, particularly with shorter focal lengths and more forgiving image scales.
That does not mean every HEM27EC automatically becomes an unguided imaging mount. Focal length, pixel scale, exposure length, polar alignment, payload geometry, seeing, and the level of star quality you expect all still matter.
The better way to think about the encoder is that the RA axis is already correcting itself before an external guider enters the picture.
Why the EC Version Can Guide Differently
The encoder also changes the way you may want to guide the mount.
On a non-encoder strain-wave mount, short guide exposures are often useful because the guider has to react quickly to the RA tracking error. That can become inconvenient with an off-axis guider, where guide stars may be too faint for extremely short exposures.
iOptron specifically recommends a different strategy with the high-precision encoder version. Because the encoder is already handling the faster RA error internally, external guide corrections can be spaced farther apart and used primarily to correct slower effects such as polar-alignment error, atmospheric refraction, and flexure.
Guide cadences in the neighborhood of 5 to 10 seconds are a useful starting point suggested by iOptron for its encoder-equipped strain-wave mounts. That is not a universal setting, but it illustrates an important EC advantage: the guider can spend more time collecting signal while the encoder continues controlling RA between guide corrections.
The 8409 hand controller also gives you two RA-guiding choices. “Allow R.A. Guiding” accepts external RA guide corrections while the encoder continues working between them. “Filter R.A. Guiding” ignores external RA guide commands and lets the encoder handle RA while the guider continues correcting declination.
Which approach works best depends on the telescope and imaging system. Judge the result from the stars in the actual subframes rather than trying to produce the smallest possible RMS number on a guide graph.
iPolar Completes the Package
The H274A adds iOptron's electronic polar scope directly to the HEM27EC.
Instead of looking through a conventional polar-scope reticle, iPolar photographs a roughly 13° field around the celestial pole and plate solves the star field. The software then shows the relationship between the mount's RA axis and the true celestial pole.
You make the altitude and azimuth adjustments while watching the result on screen. When the mount-axis indicator and celestial-pole indicator coincide, the polar alignment is complete.
Polaris itself does not have to be visible. The same applies to Sigma Octantis in the Southern Hemisphere. Enough of the surrounding polar-region sky still needs to be visible for the software to successfully identify the star field, but you are not dependent on seeing one particular star.
iOptron specifies maximum iPolar alignment precision at approximately 30 arcseconds.
Why Polar Alignment Matters Even More Here
The RA encoder is very good at correcting right-ascension tracking error. It cannot correct declination drift caused by polar misalignment.
That makes accurate polar alignment especially valuable if you plan to experiment with unguided imaging. The better the polar alignment, the less unwanted DEC movement develops during the exposure while the encoder handles the RA drive.
For guided imaging, good alignment still reduces the amount of declination correction the guider has to make and helps minimize field rotation over long sessions.
iPolar and the RA encoder therefore solve two different problems that work particularly well together: iPolar aligns the mount's axis accurately with the sky, while the encoder improves the tracking of that axis once the exposure begins.
Unguided Imaging
The encoder makes unguided imaging a realistic option to test rather than merely a theoretical possibility.
At shorter focal lengths, HEM27EC owners have reported successful multi-minute unguided exposures with round stars. That can make for an exceptionally compact travel system: telescope, camera, mount, and iPolar without a separate guide scope and guide camera.
But results vary. One system can perform beautifully at 500 or 600mm and become much less forgiving at 1,000mm. Camera pixel size, payload, polar alignment, seeing, and the individual mount all affect the result.
At longer focal lengths or fine image scales, guiding remains the safer way to maximize the percentage of usable subframes.
The encoder's benefit does not disappear when you add a guider. The guider simply begins with much less raw RA tracking error to correct.
29.7 Pounds Without a Counterweight
Underneath the encoder and iPolar is still one of the lightest mounts capable of carrying a serious astrophotography system.
iOptron rates the HEM27EC for 29.7 lb (13.5 kg) without a counterweight while the mount head weighs only 8.15 lb with its saddle installed.
There is an important qualification to that payload number. iOptron bases the rating on the payload's center of gravity being approximately 200mm from the RA rotation axis, or an optical tube around 220mm in diameter.
A compact 25-pound astrograph and a long 25-pound refractor therefore do not present the same load to the mount. Longer tubes, large rear-mounted imaging trains, and wind-sensitive systems deserve additional margin below the published rating.
The optional counterweight shaft and weight raise the published payload capacity to 44 lb and can also be useful with certain larger or more demanding configurations even when they remain below the basic counterweight-free rating.
Why iOptron Calls It a Hybrid
The HEM27EC is neither a conventional German equatorial mount nor a dual-strain-wave mount.
Right ascension uses strain-wave gearing because that is where high torque and counterweight-free operation provide the greatest practical advantage.
Declination uses iOptron's worm-and-belt system, which the company describes as backlash-free. The DEC axis includes a gear switch so it can be released for balancing.
No conventional RA balancing is required. That is one of the reasons the HEM27EC can go from carrying case to imaging setup so quickly.
From the Cloudy Nights Community
HEM27EC owners on Cloudy Nights provide a useful reality check on both the encoder and unguided-imaging claims.
One owner tested repeated five-minute unguided exposures at 560mm focal length and reported round stars after dialing in the system. With a heavier and longer refractor, that same owner found that adding a counterweight improved the unguided performance in certain telescope positions.
Another owner approached the HEM27EC hoping the encoder would eliminate guiding at medium focal lengths and ultimately found that guiding was still preferable for his system. What the encoder did allow was a longer guide cadence, making longer-focal-length telescopes and off-axis guiding more practical.
That second experience lines up well with iOptron's own guidance for its high-precision encoder mounts: let the encoder handle the faster RA tracking behavior and use the external guider primarily for the slower errors that remain.
Those two owner experiences are not contradictory. They show why the EC model should not be sold with a blanket promise of unguided imaging. The encoder materially improves the RA tracking platform, but the final result still depends on focal length, payload, polar alignment, guiding strategy, and the complete imaging system.
A Few Setup Details Worth Knowing
The HEM27EC shares the same mechanical details as the standard HEM27.
The altitude and azimuth locks use socket-head hardware rather than large hand knobs, so keeping the correct hex tool with the mount makes field setup easier.
The latitude mechanism normally covers two ranges, 15–41° and 39–65°. Moving between them requires relocating hardware, so check the mount configuration before traveling a significant distance north or south.
The saddle is also convertible rather than instantly dual-width. It ships configured for Vixen plates, and converting to Losmandy-D requires repositioning and flipping parts of the saddle assembly.
Those aren't reasons to avoid the mount, but they're useful things to know before discovering them under a red flashlight.
What's Included
- iOptron HEM27EC hybrid strain-wave equatorial mount head
- High-precision RA encoder with Real-Time PEC
- Factory-installed iPolar electronic polar scope
- Vixen/Losmandy-D convertible dovetail saddle
- Go2Nova 8409 hand controller
- 6P6C coiled hand-controller cable
- 12V/5A AC adapter for indoor use
- USB cable for mount control
- Mini-USB cable for iPolar
- Soft carrying case
Not included: tripod, counterweight shaft, or counterweight.
Frequently Asked Questions
What does the EC version add to the standard HEM27?
The HEM27EC adds a high-precision encoder to the right-ascension axis along with iOptron's Real-Time Periodic Error Correction. The hybrid drive, payload capacity, hand controller, and other major mechanical features remain essentially the same.
What does this H274A add over the HEM27EC without iPolar?
This version includes iOptron's factory-installed iPolar electronic polar scope. The encoder and mount mechanics are the same; the difference is the dedicated polar-alignment camera built into the mount.
Can I image without guiding?
Potentially. iOptron says the RA encoder provides enough tracking accuracy that many users may choose to image unguided, particularly at shorter focal lengths. Owner reports include successful multi-minute unguided imaging, but results depend on focal length, pixel scale, payload, polar alignment, and the individual system.
Should I guide the HEM27EC differently from the standard HEM27?
Usually. A standard strain-wave mount often benefits from rapid corrections. On the HEM27EC, the encoder is already handling much of the faster RA tracking error. iOptron therefore recommends experimenting with longer guide cadences, often around 5 to 10 seconds, so the guider concentrates on slower errors.
What does “Filter R.A. Guiding” do?
It tells the mount to ignore external RA guide commands and let the high-precision encoder handle right ascension while the guider continues correcting declination. “Allow R.A. Guiding” accepts external RA corrections while the encoder continues working between guide pulses.
Do I need to see Polaris to use iPolar?
No. iPolar plate solves the surrounding polar-region star field, so Polaris itself does not have to be visible. Enough surrounding sky must still be visible for the software to identify the field.
How accurately can iPolar align the mount?
iOptron specifies maximum polar-alignment precision of approximately 30 arcseconds.
Does iPolar require a computer?
Yes. iOptron's official iPolar software runs on 64-bit Windows. The camera connects by USB during alignment. Once polar alignment is complete, the iPolar computer connection is not required simply for normal tracking.
Does iPolar replace guiding?
No. iPolar handles polar alignment. The RA encoder improves right-ascension tracking. Guiding corrects whatever tracking errors remain during the exposure. They solve different parts of the imaging problem.
How much can the HEM27EC carry without a counterweight?
iOptron rates it for 29.7 lb (13.5 kg) without a counterweight. The rating assumes the payload center of gravity is approximately 200mm from the RA axis, so telescope geometry matters along with total weight.
How much can it carry with a counterweight?
With the optional counterweight system, iOptron publishes a maximum payload of 44 lb (20 kg), subject to the same payload-geometry considerations.
Does it support autoguiding?
Yes. The HEM27EC includes an ST-4-compatible autoguider port and also supports software-based pulse guiding. The EC version additionally lets you choose whether external RA guide commands are accepted or filtered.
What tripod fits it?
The HEM27EC can mount directly to compatible iOptron CEM26/GEM28/HEM27/HAE29 tripod systems, including the matched LiteRoc and compatible carbon-fiber tripod. A MiniPier can provide additional clearance for longer refractors or deep rear-mounted imaging trains.
Final Thoughts
The HEM27EC with iPolar is the most complete version of iOptron's remarkably light HEM27 platform because its two upgrades solve two different parts of astrophotography.
The high-precision RA encoder and Real-Time PEC improve the tracking behavior of the strain-wave drive. The built-in iPolar camera makes it easier to put the mount's RA axis accurately on the celestial pole before the exposure begins.
Underneath both is still the feature that made the HEM27 interesting in the first place: 29.7 pounds of counterweight-free capacity in a mount head weighing just 8.15 pounds.
At forgiving image scales, the combination can make unguided imaging practical. At longer focal lengths, the encoder can allow a more relaxed guiding strategy while iPolar provides the accurate alignment that helps keep declination drift under control.
If you want the HEM27's portability, the EC model's improved RA tracking, and a dedicated polar-alignment system already built into the mount, this is the version that puts all three together.
