• 1. Overview
• 2. Compact Tracking Mounts - SkyTracker, SkyGuider Pro, and SkyHunter
• 3. iOptron Center-Balance EQ Mounts (CEM Series)
  • 3.1 Overview
  • 3.2 CEM26 Center-Mounted Equatorial Mount
  • 3.3 CEM40 Center-Mounted Equatorial Mount
  • 3.4 CEM70 Center-Mounted Equatorial Mount
  • 3.5 CEM120
• 4. iOptron German EQ Mounts
  • 4.1 Overview
  • 4.2 GEM28 German Equatorial Mount
  • 4.3 GEM45 German Equatorial Mount
  • 4.4 SmartEQ Mounts
• 5. Hybrid Harmonic Mounts
  • 5.1 Overview
  • 5.2 HEM27 Harmonic Mount
• 6. Alt-Azimuth Mounts
• 7. Summary

1. Overview

iOptron is one of the leading manufacturers of equatorial mounts, telescopes, and accessories for the amateur astronomy community. The company established its reputation for innovation by introducing their center-balanced equatorial mounts (CEM) that offer improved performance and cable management. They’ve also leveraged their experience with these mounts to design and manufacture more traditional German equatorial mounts (GEM) as well as compact mounts for wide-field astrophotography and a line of Go-To altazimuth mounts. iOptron mounts are particularly known for their ability to carry heavier payloads relative to their weight (the ‘weight-to-payload’ ratio) compared to many other German equatorial mounts.

Most iOptron mounts are sold with a selection of accessories to form a complete package that includes mount head, tripod, and some form of polar alignment scope. There are many packages for each model of iOptron mount which can make it challenging to select the right one for a particular budget or application. This buyer’s guide sorts through the various package options for iOptron mounts including their compact equatorial mounts, CEM mounts, GEM mounts, and altazimuth mounts. It also lists the most common accessories available for each mount for those looking to upgrade or replace their existing hardware.

2. Compact Tracking Mounts - SkyTracker, SkyGuider Pro, and SkyHunter

For nightscape imagers looking for a tracking platform for their mirrorless or DSLR cameras, iOptron offers three solutions - the SkyTracker Pro, SkyGuider Pro, and SkyHunter.

The SkyTracker has a capacity of 6.6lbs, making it suitable for tracking with cameras with relatively small wide-field lenses up to 30mm, approximately. The SkyTracker includes a removable base that aids with altitude adjustment for polar alignment. Base and tracker together weigh about 2.5lbs (including battery). The SkyTracker Pro comes in two versions, one with a standard AccuAlign polar scope for manual polar alignment and one with the iOptron iPolar scope for a more automated alignment when connected to a PC running iOptron’s iPolar software. The mirrorless or DSLR camera is best mounted on a ballhead (sold separately) to help aim anywhere in the sky when polar aligned. The tracker itself or the base-plus-tracker can be mounted on a photo tripod (also not included). The SkyTracker includes a battery rechargeable through a standard USB cable. The light weight and compact size of this little tracking mount makes it ideal for backpacking or travel.

Figure 1 – A configuration of the iOptron SkyGuider Pro with counterweight, iPolar, and tripod.

The SkyGuider Pro offers a more heavy-duty design than the SkyTracker. It can handle a payload up to 11lbs despite a head that weighs only 3.2lbs (including base and battery). The SkyGuider Pro is designed as a more traditional German equatorial mount with a small counterweight and tracking motor for the polar axis. There is no motorized operation in the declination axis. The tracker works with the iOptron 8408 hand controller in a limited capacity - again, with operation in polar axis only. The mount also includes an autoguiding port for guiding in the polar axis.

The SkyGuider Pro is slightly less compact than the SkyTracker Pro, but the extra payload capacity helps in tracking with larger cameras and many lenses up to about 200mm focal length. Some imagers even mount small telescopes such as a William Optics RedCat 51 (250mm focal length) on the SkyGuider Pro and achieve acceptable results, but this pushes the limits of this compact GEM. The SkyGuider Pro also comes with either a manual polar scope or the iPolar scope and software package that simplifies polar alignment. A tripod is not included with either configuration.

Figure 2 -  The iOptron SkyHunter mount in equatorial configuration with a iPolar scope.

The newer iOptron SkyHunter mount is the most feature rich of the compact iOptron mounts. It features motors and encoders on both the polar and declination axes, four tracking speeds, and control with a smartphone/tablet app or the iOptron 8410 hand controller (sold separately), or through computer control. It weighs 2.9 lbs (including the battery) and has a load capacity of 11 lbs, large enough to support cameras or a small telescope. The SkyHunter is availalbe as an alt-azimuth mount with tripod or in alt-azimith/equatorial configurations with a tripod, without a polar scope, or with an iPolar scope that includes a camera and software that guides the user through a precise polar alignment process on a PC.

iOptron accessories for the SkyTracker and SkyGuider Pro including a lightweight tripod (#3221) designed especially for these mounts. iOptron also offers a ball head (#3305a) to attach a DSLR or mirrorless camera to these small mounts. The iOptron hand controller (#8408) also works - with limited functionality - with the SkyGuider Pro, while the SkyHunter works fully with the iOptron #8410 hand controller.

3. iOptron Center-Balance EQ Mounts (CEM Series)

3.1 Overview

iOptron’s best-known innovation is the center-balanced equatorial mount (CEM). What makes these mounts different from a traditional German equatorial mount (GEM)? In a GEM, the declination axis and the counterweight are on the same side of the mount. By contrast, in the iOptron CEM design, the declination axis is offset to the opposite side of the base from the counterweight. This helps transfer the centre of gravity of the overall load centrally over the shaft of the RA axis and nearly directly over the tripod or pier. In principle, this helps improve stability. The CEM design makes it easier to make fine adjustments to the mount’s altitude, and in some cases, makes cable management easier. It also prevents blockage of the polar scope by the declination shaft, a common nuisance in traditional GEMs, which means the polar scope is accessible at all times.

iOptron’s CEM series currently includes these models:

• CEM26 with a maximum capacity of 26lbs
• CEM40 with a maximum capacity of 40lbs
• CEM70 with a maximum capacity of 70lbs
• CEM120 with a maximum capacity of 115lbs

As with most equatorial mounts, loading the mount to maximum capacity and careful balancing usually results in enough stability for visual observing. But for imaging applications, a lesser payload is recommended to ensure good stability and tracking.

While some iOptron CEM models can be ordered with the mount head only and matched with a tripod and other accessories, iOptron offers most of their CEM-series in a wide array of packages that make it easier to choose and order a mounting system as a single part number. As described in the following sections, the packages for CEM systems include the mount head and a selection of accessories such as a standard 1.5” or heavier-duty LiteRoc steel tripod, an AccuAlign polar alignment scope or iPolar camera system, and a hard case. Some CEM mount heads also come in versions that include built-in error correction (EC models), or a mounting plate for an Intel NUC minicomputer (NUC models). The CEM70 and CEM120 models are also available with a built-in autoguiding system (G models).

3.2 CEM26 Center-Mounted Equatorial Mount

With a payload capacity of 26lbs, the iOptron CEM26 is an ideal match for observers and imagers with small refractors up to about 100mm aperture or compound telescopes up to 200mm aperture. For best performance for imaging, the total load on the telescope should not approach this specified payload limit but should be kept to below 15lbs, approximately. The mount itself, not including counterweight, weighs just 10lbs.

Figure 3 – The iOptron CEM26 center-mounted equatorial mount and tripod

iOptron offers a number of packages based around the CEM mount head. Each package includes the mount head, Go2Nova® 8409 Hand Controller, and one or more of the following accessories:

• Heavy-duty stainless-steel tripod with 1.5” steel legs
• Upgraded LiteRoc tripod with a die-cast aluminum top and heavy-duty stainless steel tripod legs with a 1.75” diameter upper leg section and a 1.5” diameter lower section
• AccuAlign Polar Scope for manual polar alignment
• iPolar that includes a camera and software that guides the user through a precise polar alignment process on a PC (a mount comes with either an AccuAlign polar scope or iPolar, but not both)
• An aluminum hard case for the mount head

iOptron CEM26 mounts feature built-in WiFi, a positive lock gear engagement system that makes it easy to use even when wearing gloves, and a recordable permanent periodic error correction (PPEC) to repeat optimal PEC training sessions. Standard CEM26 mounts feature a periodic error of <±10 arcseconds. The upgraded ‘EC’ version of the mount includes a high-resolution optical encoder with real-time periodic error correction with a tracking accuracy of <0.3 arcsec RMS.

Table 2 summarizes the current packages available for the iOptron CEM26 mount.

iOptron offers the hand controller for the CEM26 (and GEM28) mount as a separate part for those looking for a replacement or upgrade. They also offer a GPS module for the CEM26 that also work with the CEM40, the GEM28, and GEM45 mounts.

3.3 CEM40 Center-Mounted Equatorial Mount

With a payload capacity of 40lbs, the iOptron CEM40 carries moderately-large refractors, compound scopes, and Newtonians. For best performance for imaging, the total load on the telescope should not approach this specified payload limit but should be kept to below 25lbs, approximately. The mount itself, not including counterweight, weighs just 17.4lbs.

iOptron offers a number of packages based around the CEM mount head. Each package includes the mount head, Go2Nova® 8407 Hand Controller, and one or more of the following accessories:

• Heavy-duty stainless-steel tripod with 1.5” steel
• Upgraded LiteRoc tripod with a die-cast aluminum top and heavy-duty stainless steel tripod legs with a 1.75” diameter upper leg section and a 1.5” diameter lower section
• iPolar that includes a camera and software that guides the user through a precise polar alignment process (CEM40 packages do not come with the standard AccuAlign polar scopes)
• An aluminum hard case for the mount head

iOptron CEM40 mounts feature built-in GPS, optional WiFi, a positive lock gear engagement system which makes it easy to use even when wearing gloves, and a recordable permanent periodic error correction (PPEC) to repeat optimal PEC training sessions. Standard CEM40 mounts feature a periodic error of <±7 arcseconds. The CEM40 mount also includes a dual saddle that accommodates Losmandy or Vixen dovetails.

The upgraded ‘EC’ version of the mount includes a high-resolution optical encoder with real-time periodic error correction with a tracking accuracy of <0.25 arcsec RMS. The CEM40G version of the mount also includes a built-in iGuider camera. Some CEM40 packages include on the mount head a bracket to mount an Intel NUC minicomputer.

The LiteRoc tripod is also available as a stand-alone accessory.

Table 3 summarizes the current packages available for the iOptron CEM40 mount.

3.4 CEM70 Center-Mounted Equatorial Mount

With a payload capacity of 70lbs, the iOptron CEM70 carries large refractors, compound scopes, and Newtonians. For best performance for imaging, the total load on the telescope should not approach this specified payload limit but should be kept to below 40lbs, approximately. The mount itself, not including counterweight, weighs 30lbs.

iOptron offers a limited number of packages based around the CEM70 mount head. Each package includes the mount head, Go2Nova® 8407 Hand Controller, an iPolar polar alignment system, and a hard case. In addition to the standard CEM70, versions are available that include the iGuider autoguiding camera, EC (periodic error correction) for tracking down to <0.35 arcseconds, and a mounting plate for a NUC microcomputer. The CEM70 series also includes a cable management system and GPS. The CEM70 with integrated iGuider includes WiFi, and iOptron also has select other models of the CEM70 available with WiFi (see Table 4).

None of the current CEM70 packages include a tripod, so it must be ordered separately. iOptron offers a LiteRoc tripod for the CEM70 (which also works with the older iOptron iEQ45 and CEM60 mounts). iOptron also offers a combination tripod and pier - a Tri-Pier - that is available with a rolling case or without the case.

Some models of the CEM70 are available in an 'EC2' version with high-resolution encoders on each axis that enables the mount to perform precise dual-axis tracking. Using advanced sky modeling, the CEM70EC2 mounts also account and adjust for polar alignment error and changes in atmospheric (refractive) distortion. Fixed home sensors on each axis allow the mount to save alignment models after power off to be used on future nights.

Table 4 summarizes the current packages available for the iOptron CEM70 mount.

3.5 CEM120

The CEM120 is the largest-capacity mount in the iOptron product line with a rated capacity of 115lbs. It’s ideal for large telescopes or multiple telescopes. The mount head weighs 57lbs. The CEM120 series includes an advanced cable management system, WiFi, a LAN connection, GPS, and precision stepper motors. It comes with the Go2Nova® 8407 Hand Controller for go-to operation.

Figure 4 – The mount head of the iOptron CEM120 equatorial mount

Unlike the lighter-duty CEM mounts described above, the CEM120 mount head is not currently offered in packages with tripods, polar scopes, or guide cameras; these are sold separately. The mount head is available in three versions:

• The standard CEM120 (iOptron product code 7300) with a low periodic tracking error of +/-3.5 arcseconds
• The CEM120EC (iOptron product code 7301) with real-time periodic error correction with a tracking accuracy of <0.15 arcsec RMS
• The CEM120EC2 (iOptron product code 7302) has high-resolution encoders on each axis that enables the mount to perform precise dual-axis tracking. Using advanced sky modeling, the CEM120EC2 also accounts and adjusts for polar alignment error and changes in atmospheric (refractive) distortion. Fixed home sensors on each axis allow the mount to save alignment models after power off to be used on future nights.

To support this large mount, iOptron offers their Tri-Pier 360 for field use or their Permanent Pier.

4. iOptron German EQ Mounts

4.1 Overview

While iOptron is known for its center-balanced equatorial mounts, it also makes a series of German equatorial mounts (GEM) for those who prefer this more traditional design. These mounts also allow a higher altitude adjustment up to 70 degrees compared to about 60 degrees for CEM mounts. iOptron also applied their understanding and experience with center-balanced mounts to improve the ratio of capacity-to-weight of their German equatorial mounts, compared to many competitive offerings.

iOptron’s GEM series currently includes the GEM28 with a maximum capacity of 28lbs, and the GEM45 with a maximum capacity of 45lbs. As with most equatorial mounts, loading the mount to maximum capacity and careful balancing usually offers enough stability for visual observing. But for imaging applications, a lesser payload is recommended to ensure good stability and tracking.

While many iOptron GEM mount models can be ordered with the mount head only and then matched with a tripod and other accessories (as with their CEM mounts), iOptron offers most of their GEM series in a wide array of packages that make it easier to choose and order a mounting system as a single part number. As described in the following sections, the GEM systems include the mount head and a selection of other accessories such as a standard 1.5” or heavier-duty LiteRoc tripod, polar alignment scope or iPolar camera, and a hard case. Some GEM mount heads also come in versions that include built-in error correction (EC models), or a mounting plate for an Intel NUC minicomputer (NUC models).

4.2 GEM28 German Equatorial Mount

The iOptron GEM28 has a maximum capacity of 28lbs and makes an ideal match for observers and imagers with small refractors up to about 100mm aperture or compound telescopes up to 200mm aperture. For best performance for imaging, the total load on the telescope should not approach this specified payload limit but should be kept to below about 15lbs, approximately. The mount itself, not including counterweight, weighs just 10lbs giving it a payload-to-weight ratio of 2.8.

iOptron offers a number of packages based around the GEM28 mount head. Each package includes the mount head, Go2Nova® 8409 Hand Controller, and one or more of the following accessories:

• Heavy-duty stainless-steel tripod with 1.5” steel
• Upgraded LiteRoc tripod with a die-cast aluminum top and heavy-duty stainless steel tripod legs with a 1.75” diameter upper leg section and a 1.5” diameter lower section
• AccuAlign Polar Scope for manual polar alignment
• iPolar that includes a camera and software that guides the user through a precise polar alignment process (a mount comes with either a polar scope or iPolar, but not both)
• An aluminum hard case for the mount head

Like the CEM26 mount, the iOptron GEM28 features built-in WiFi, a positive lock gear engagement system which makes it easy to use even when wearing gloves, and a recordable permanent periodic error correction (PPEC) to repeat optimal PEC training sessions. Standard GEM28 mounts feature a periodic error of <±10 arcseconds. The upgraded ‘EC’ version of the mount includes a high-resolution optical encoder with real-time periodic error correction specifies accurate tracking of <0.3 arcsec RMS.

Table 5 summarizes the current packages available for the iOptron GEM28 mount.

iOptron offers the hand controller for the GEM28 mount as a separate part for those looking for a replacement or upgrade. They also offer a GPS module for the GEM28.

4.3 GEM45 German Equatorial Mount

With a payload capacity of 45lbs, the iOptron GEM45 carries moderately-large refractors, compound scopes, and Newtonians. For best performance for imaging, the total load on the telescope should not approach this specified payload limit but should be kept to below 25lbs, approximately. The mount itself, not including counterweight, weighs just 17.5bs.

Figure 5 – The iOptron GEM45 German equatorial mount with a mount for a NUC microcomputer

iOptron offers a number of packages based around the GEM45 mount head. Each package includes the mount head, Go2Nova® 8407 Hand Controller, and one or more of the following accessories:

• Heavy-duty stainless-steel tripod with 1.5” steel
• Upgraded LiteRoc tripod with a die-cast aluminum top and heavy-duty stainless steel tripod legs with a 1.75” diameter upper leg section and a 1.5” diameter lower section
• iPolar that includes a camera and software that guides the user through a precise polar alignment process (GEM45 packages do not come with the standard AccuAlign polar scopes)
• An aluminum hard case for the mount head

iOptron GEM45 mounts feature built-in GPS, a positive lock gear engagement system which makes it easy to use even when wearing gloves, and a recordable permanent periodic error correction (PPEC) to repeat optimal PEC training sessions. Standard GEM45 mounts feature a periodic error of <±7 arcseconds. The GEM45 mount also includes a dual saddle that accommodates Losmandy or Vixen dovetails.

The upgraded ‘EC’ version of the mount includes a high-resolution optical encoder with real-time periodic error correction with a tracking accuracy of <0.25 arcsec RMS. The GEM45G version of the mount also includes a built-in iGuider camera. Some GEM45 packages include on the mount head a bracket to mount an Intel NUC minicomputer.

Some GEM45 packages do not include a tripod, but the LiteRoc tripod is available as a stand-alone accessory. A separate WiFi module is also available as an accessory.

Table 6 summarizes the current packages available for the iOptron GEM45 mount.

4.4 SmartEQ Mounts

iOptron also offers more compact and affordable German equatorial mounts for visual observers or wide-field imagers with smaller scopes. The SmartEQ Pro mounts have the following key features:

• 11lbs payload (excluding the counterweight) in a mount that weighs 6.2 lbs
• Go2NovaTM 8408 controller with Advanced GOTONOVA® GoTo Technology
• Low power consumption (the mount can operate on 8 AA batteries for 16 hours of consecutive tracking)
• ST-4 compatible Guiding Port
• Vixen-type dovetail saddle

5. Hybrid Harmonic Mounts

5.1 Overview

Like other mount manufacturers, iOptron has developed a platform for telescope mounts with a harmonic drive which supports relatively high loads in a compact mount head that, in many applications, does not need a counterweight. iOptron's harmonic mounts are of a hybrid design that incorporates a strain wave gear on the polar axis and a more conventional backlash-free worm gear and belt on the declination axis. Worm gears have a significantly lower periodic error (PE) than strain wave gears, and the hollow shaft of worm gears allows for easier cable management and enabled the insertion of a polar scope in the mount. Worm gears cost less to manufacture, so iOptron's hybrid harmonic design offers the performance of a harmonic mount at prices that are less than competing designs.

iOptron also implements periodic error correction (PEC) on their HEM mounts. With a strain wave gear, PEC is trickier since the PE curve varies from point to point and according to conditions. iOptron incorporats sensors in the HEM mount to enable phase matching and special algorithms that make PEC more effective. iOptron HEM mounts are designed to work in equatorial mount only, with no AZ mode, and they require autoguiding because of the high intrinsic PE of the strain wave gear in the polar axis and the cable management layout in the declination axis. The PE in the polar axis, though unspecified, it typically 2-10x that of the declination axis.

Figure 7 – An iOptron HEM27 hybrid harmonic mount

5.2 HEM27 Harmonic Mount

iOptron's first hybrid harmonic mount, the HEM27, has a maximum payload of 13.5kg (29.7 lbs) without the need for a counterweight and up to 21kg (46lbs) with an optional counterweight. The mount head weighs about 8.2 lbs.

The HEM27 mounts is also available in an error-corrected (EC) version that use high-precision encoders to correct PE in real time. The high precision encoder used in HEM27EC, for example, is the same as in CEM26EC/GEM28EC and should be able to reduce the mount PE significantly, to a level similar to CEM26EC/GEM28EC, and are capable of imaging without autoguiding.

For observers in tropical locations, iOptron also offers a special version of the HEM27 mount that works at latitudes of 0-22 degrees latitude. These are available as special orders.

All HEM27 mounts include built-in WiFi.

The current packages of iOptron HE27 harmonic equatorial mounts include:

• HEM27A EQ Mount Head with iPolar scope and soft carrying case
• HEM27EC EQ Mount Head with high-resolution encoders and error correction, iPolar scope and soft carrying case
• HEM27 EQ Mount Head and soft carrying case

The HEM-series mount packages listed below do not include a tripod, but iOptron offers a dedicated carbon-fiber field tripod for the HEM27 that also works with several other iOptron CEM and GEM mounts.

6. Alt-Azimuth Mounts

For those who want the convenience of computerized Go-To operation but don’t need an equatorial mount, iOptron also makes a heavy-duty GoTo alt-azimuth mount, the AZ Mount Pro. It has a capacity of 33lbs for a primary payload and 13lbs for a counter-balanced secondary payload with a mount head that weighs only 13lbs. The mount includes a GPS receiver that facilitates a partially automated alignment procedure. It includes the Go2Nova® 8407 hand controller, a built-in WiFi adapter, and an aluminum hard case.

Figure 8 – The mount head for the iOptron AZ Mount Pro altazimuth mount.

7. Summary

As this buyer's guide shows, iOptron has a comprehensive line of equatorial and alt-azimuth mounts for amateur astronomy. These mounts are designed to suit a wide range of budgets and applications from nightscape imaging with small mirrorless cameras to astrophotography and research with large telescopes. As iOptron continues to introduce new products, this guide will be updated to reflect changes to their product line.