Technical Specs
The EQM-35i is based on the regular EQ-3 mount, which has essentially the same generic design as the Celestron CG-4 and Orion SkyView Pro mounts but with electronics added. It shares their 1.75” steel tripod legs (also used by the HEQ5i Pro) and other basic mechanical features. It’s easy to tell that the EQM-35i was a bit of an ad hoc design, as the motor housings awkwardly budge from the sides of both the right ascension and declination axes, with cables required to connect the declination axis to the right ascension motor board or housing, which itself plugs into a computer control hub attached to the tripod legs rather than an internal board on the mount head. These cables can get caught on the mount/tripod if you are not careful.
For visual use, the EQM-35i is rated to a 22-pound capacity. In reality, the limit is closer to 15 lbs. or so. An 8” Schmidt-Cassegrain (slightly over 15 lbs when loaded with accessories) is too heavy for the mount, as is an 8” Newtonian or 6” refractor. A 6” Newtonian, 6” Schmidt-Cassegrain, 5” Maksutov, or 4-5” refractor would be our recommendations for the largest telescopes that can be comfortably loaded onto the mount for visual use.
Astrophotographers usually consider ½ to ⅔ of the stated weight capacity of an equatorial mount to be the limit for deep-sky imaging. The stepper motors and 180-tooth worm gear in the EQM-35i would theoretically provide accurate tracking for an 11- to 15-lb payload, but are limited by the small size of the gearing. In practice, 9 lbs or so, corresponding to a 5” Newtonian or a lightweight doublet 80mm refractor, is about as much as you should expect to be able to achieve good results with (provided you use an autoguider, of course). You get two standard 7-lb counterweights with the EQM-35i, which is all you should ever need, though the counterweight shaft accepts any ¾” diameter counterweights from other mounts.
Unusually, the EQM-35i’s entire declination axis can be simply removed and replaced with parts from the Sky-Watcher Star Adventurer to convert it into a simpler tracker and reduce weight/volume for travel. In practice, this would still make little sense due to the bulky nature of the EQM-35i’s tripod and the difficulty in adapting the mount head to another one. Like many equatorial mounts, you can also take the counterweight shaft off the mount head for transport to save space.
For attaching your telescope, the EQM-35i includes a relatively basic Vixen-style dovetail saddle, and a polar scope is built into the mount for alignment, though the reticle is not illuminated and can be difficult to see in the dark.
Software Compatibility
To control the mount, the EQM-35i includes a SynScan Wi-Fi dongle, which allows for wireless control through the SynScan Pro app or similar apps such as SkySafari Pro on Apple, Android, or Windows devices. A SynScan hand controller can also be plugged in, or you can directly connect the EQM-35i to your computer with an EQDIRECT USB adapter cable, which is the preferred choice of most astrophotographers. An ST-4 port is built into the control hub attached to the tripod leg for autoguiding, though you’d need yet another long, snag-prone cable to plug it in, and guiding through an EQDIRECT cable would make more sense.
Using the EQM-35i for Visual Astronomy & Planetary Imaging
The EQM-35i is fairly easy to use for visual astronomy, and its setup is only slightly more complex than that of an alt-azimuth GoTo mount such as the AZ-GTi or Virtuoso GTi. The only differences are the added steps of polar alignment and balancing on two axes instead of just one axis. When using it for solar, lunar, and planetary imaging, you should follow the same procedures as you would with any other mount and use an eyepiece in your telescope to align and center your target object the same as you would for visual observation.
To set up the EQM-35i, you simply assemble and level the tripod, put the counterweights and telescope on, balance it, and then perform alignment. Balance is required in both the right ascension and declination axis: you balance the telescope in the declination axis (either with the Vixen-style dovetail itself or within tube rings), and balance the right ascension axis by sliding the counterweights on their shaft. You then polar align the mount with the polar scope as best you can (accuracy is less critical for planetary imaging or pure observation), and power up the mount. The SynScan app will then prompt you to do a GoTo alignment, which is a straightforward process that involves centering your telescope on two or three bright stars. After completing the alignment, you’re ready to begin using the mount.
Using the EQM-35i for Deep-Sky Astrophotography
While it’s possible to operate the EQM-35i for deep-sky imaging without a PC, doing so does not allow for autoguiding the mount, which is necessary to keep it on target during long exposures. It is generally considered best practice to run everything with a computer and via a direct cabled connection. This will allow for minimal fuss and maximum control over all of the mount’s abilities.
Using an EQDIRECT cable allows you to operate the EQM-35i with the ASCOM protocol, EQMod control software, and capture software such as NINA or Sequence Generator Pro, along with software such as PHD2 to control autoguiding. NINA, SGP, and other sequence/capture software lets you bypass doing a GoTo alignment once the mount is suitably polar aligned and powered up by simply attempting to slew to your target and plate solving with short camera exposures until you have achieved perfect centering and framing. The software will then autonomously run your mount, guiding, cameras, and any other accessories like filter wheels, and even perform functions like a meridian flip or going to additional targets on its own. You can go to sleep or otherwise leave your EQM-35i to run itself once you have properly configured such a system.
Should I buy a Used Sky-Watcher EQM-35i?
A used EQM-35i (or EQM-35 Pro, which is identical apart from including a SynScan hand controller instead of a WiFi dongle) can be a great choice, provided it is fully functional and not missing any parts, as replacement parts for these mounts are harder to find than for larger and more well-supported models. Thankfully, many of the parts meant for the Celestron CG-4, such as its polar scope, are compatible as spares. Always try to buy from a reputable vendor or a seller who has used it before.
Alternative Recommendations
The EQM-35i is a great mount, though there are a few other options which may be worth considering:
- The Sky-Watcher HEQ5i Pro is essentially the same in form factor and weight as the EQM-35i but has significantly better weight capacity for both visual and astrophotography use as well as more versatile accessory/upgrade options, fewer exterior cables and other hardware, a polar scope illuminator, and better tracking/guiding accuracy.
- The Celestron Advanced VX offers far more weight capacity for visual use than the HEQ5i Pro or EQM-35i but is noticeably inferior to the HEQ5i pro in tracking/guiding accuracy with performance limitations making its actual capacity similar to that of the EQM-35i.
- The Sky-Watcher EQ6Ri Pro offers far greater payload capacity than smaller Sky-Watcher mounts with high-quality belt drives and stepper motors as well as various other integrated features.
- The Sky-Watcher Star Adventurer GTi’s more modular and portable design than the EQM-35i is ideal for traveling astrophotographers, but it’s inferior for carrying a telescope.
- For non-imaging use, the Celestron CG-4 is mechanically identical to the EQM-35i but lacks a GoTo system or drives by default.
Aftermarket Accessory Recommendations
A Polemaster and suitable adapter for the EQM-35i can make polar alignment for imaging a lot easier than attempting to use the non-illuminated stock polar scope, though it’s an expensive upgrade, especially when you could spend the money on getting a larger mount. You’ll also need either an AC power cord or some kind of power supply to run the EQM-35i, such as the Celestron PowerTank Lithium or generic rough equivalent.
