Technical Specs
As with the larger Celestron Advanced VX (which replaces the old CG-5) the Celestron CG-4 German Equatorial Mount has a decades-long history, starting with its origins as a stripped-down clone of the Vixen Super Polaris mount (the original CG-5 and now Advanced VX were based on the larger Great Polaris). The CG-4 has been roughly the same for the past 20 or so years, though it has undergone a few different tripod changes (often consisting of low-quality extruded aluminum and plastic parts) and paint jobs before settling on today’s white finish and 1.75” steel leg tripod. You can get the CG-4 on its own or bundled with one of the various 4-6” telescopes from the Celestron Omni XLT line.
The present-day Celestron CG-4 resembles a number of other nearly identically designed equatorial mounts, all of which are variants on the “EQ3” design, such as the Orion SkyView Pro and the Sky-Watcher EQM-35i, the latter of which is basically just a CG-4 with GoTo. The CG-4 has a 1.75” steel-legged tripod and features the same standard Vixen-style dovetail saddle, polar scope borehole, slow-motion cables and attachments, 0.75” diameter counterweight shaft, and other such standard hardware as many of the mounts manufactured by Synta for Sky-Watcher and Celestron. There are no plastic parts other than the fine adjustment knobs/cables in the entire CG-4 mount. Most of the metal parts are well-machined and
For visual use, the CG-4 is rated to be able to handle a 20-pound weight capacity. However, in practice, the heaviest telescope that the mount can possibly handle is around 15 lbs. An 8” Schmidt-Cassegrain, for instance, at around 16 lbs with typical eyepieces and accessories, is too heavy for the mount, as would be something like an 8” Newtonian or most 6” refractors. We recommend using a 6” Newtonian, 6” Schmidt-Cassegrain, 5” Maksutov, or 4-5” refractor on the CG-4, as well as smaller telescopes; larger scopes belong on something like the Celestron Advanced VX or Sky-Watcher EQ6Ri Pro.
The CG-4 includes a 4 lb counterweight and a 7 lb counterweight, which are all you are likely to need, though the ¾” diameter counterweight shaft will fit additional counterweights designed for other mounts so long as they have the same diameter. You can unscrew the counterweight shaft for transport. The CG-4 fits any telescope with a Vixen-style dovetail in its attached saddle.
Using the CG-4 for Visual Astronomy
The Celestron CG-4 is a manual mount, so you have to move it around the sky by unlocking its clutches, even with the optional motor drive kit, which can only be used for tracking and fine adjustments. You set up the CG-4 by extending and leveling the tripod legs, putting the mount head and spreader tray on, and then attaching counterweights, followed by the telescope. You then balance the mount by sliding the telescope along the dovetail saddle (or in its tube rings) to balance in declination, leaving the clutches unlocked, and adjusting until the telescope no longer moves under its own weight. The same process is repeated with the right ascension axis by adjusting the counterweights. After you’re done balancing the telescope for the first time, you can label the positions on the dovetail bar and counterweight shaft for quick repeated assembly.
Polar alignment of the CG-4 can be achieved by roughly sighting through the empty polar axis hole in the mount or with a polar scope, which we highly recommend purchasing. After polar alignment is done, you’re ready to use the mount. The CG-4 glides smoothly around the sky with the clutches unlocked thanks to its metal ball bearings, and you can use the provided slow-motion knobs for fine adjustment as well as tracking on the right ascension axis after you lock the clutches. The fine adjustment knobs are attached to smooth worm gears to minimize backlash or play when they are turned. You can replace them with longer cables if need be.
Using the CG-4 for Astrophotography
The Celestron CG-4 mount can be used with a telescope for planetary astrophotography, though it’s going to require constant manual adjustment for tracking or the purchase of the motor drive kit. The motor drive for the CG-4 allows for some long-exposure astrophotography capabilities with small telescopes and telephoto lenses, though you can’t control it with a PC or autoguide, and the amount you’d be spending would be nearly enough to just buy a Sky-Watcher EQM-35i or Celestron Advanced VX, either of which will have these features and superior tracking quality.
Should I buy a Used Celestron CG-4?
A used Celestron CG-4 EQ mount can be a great mount for a smaller telescope. Older versions may have aluminum tripod legs or wooden ones, but they are generally the same apart from slight functionality differences in the tripod designs and in general appearance. You can easily find spare parts, and there is little that can be damaged in these mounts besides dents to the tripod legs or outright broken metal castings (which are rare and immediately obvious).
Alternative Recommendations
The Celestron CG-4 is a nice mount, but it’s obviously not very useful for astrophotography, and visual observers may want to consider a different mount.
- The Sky-Watcher AZ-GTi has essentially the same payload capacity as the CG-4, but its alt-azimuth design is easier to aim and more compact. You also get fully motorized tracking and GoTo capabilities, but can aim the GTi manually without ruining your GoTo alignment thanks to its FreedomFind encoders.
- The Explore Scientific Twilight I can carry slightly heavier payloads than the CG-4 and has a similar well-constructed design, albeit in an alt-azimuth configuration.
- The Sky-Watcher EQM-35i is literally identical to the CG-4 apart from the addition of stepper-driven GoTo and motorized tracking, controlled via your smartphone or directly with a PC connection. It’s ideal for visual use with smaller telescopes like the CG-4 but is great for astrophotographers with smaller rigs too.
- The Sky-Watcher HEQ5i Pro shares many of the features of the EQM-35i and CG-4 but has a higher payload capacity, superior mechanical design, better tracking, and features such as an illuminator for its polar scope and a retractable counterweight shaft, despite taking up hardly any more space and weighing just a few extra pounds.
- The Celestron Advanced VX offers far more payload capacity than the HEQ5i Pro or CG-4 for visual use and planetary imaging, though for deep-sky astrophotography it’s hardly much better than the EQM-35i due to its mediocre tracking and guiding quality.
Aftermarket Accessory Recommendations
A polar scope is a must for the CG-4 to accurately polar align, and the CG-4 motor drive allows for simple hands-free tracking and replaces the provided slow-motion knobs with variable speed push button controls. There are various GoTo upgrades available for the CG-4 as well, but at that point you’d just be getting a lower quality, ad-hoc servo-driven copy of the Sky-Watcher EQM-35i at hardly any savings compared to the EQM-35i.
