CGEM/CGEM DX StellarTune™

Now features StellarDrive™-SPX ultra precision wormgears, Hybrid-Ceramic worm-gears, and StellarDrive™RX Axis bearing set as standard build in all StellarTune™ models

Our new StellarDrive™ CGEM/DX for 2020 goes even further with reprocessed crown-rings, StellarDrive™FX axis bearing set, and optimised reduction gearboxes!

CGem Options:

Standard CGem StellarTune™                      £469.00

CGem/DX StellarDrive™ SPX Wormgears      £699.00
(Stated prices are for upgrade/tune to customers own mount)

Please choose your option and pay via the website or drop your mount off and pay when you arrive - please call or e-mail to arrange drop off  02392 570283 - dave@darkframe.co.uk. 


We are proud to announce that we offer a 2 year limited warranty on all StellarTuned Celestron EQ and AZ Mounts, re-engineered to our enhanced Bonneville Build Type.


Book your mount in now - Book it in when it's cloudy not clear!

Celestron Equatorial mounts by nature are precision made products. However, due to mass production and to keep the prices lower, they are often not fettled to the best of their ability due to the variances in each mount. Various improvements can be made to transform the performance of your mount from what is a median production build this will save you the need to upgrade to a more expensive mount, providing you are happy with the payload you have. 

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EQ mounts are subject to being outside and often in the damp, so renewing the grease is often a first port of call, using a better type of grease more suited to our climate can help reduce friction. This means the motors can drive the mount a lot more accurately both unguided and guided compared to a stock mount. We service the gearboxes from what we have developed with our Ambient tuning techniques, and in doing so make them run quieter and smoother.

Also, with much more care in adjusting the worm-gears and motor drive train, they can often be made to run smoother and quieter throughout, which also benefits better tracking and periodic error reduction. 

What's the difference between a Service and a Tune and a Repair?

Our Mount Servicing is effectively to bring your tired mount back to a factory fresh setup with backlash adjustment and using standard greases and oils. However, if there is any damage, or wear, then new components may be required at extra time and cost to put right. Like a car, you cannot tune a sick motor, so we evaluate every mount before we attempt to tune it. 

Our Hypertuned mounts are better than new, with more response and less friction than a factory mount. This equates to better guided and tracking performance, as proven by our customers PHD2 guide data and their amazing images! Not only are nearly all mounts independently tested by our customers, they paid to find out how good they are. The guide logs we get back from them have helped us produce what is the most cost-effective and reliably performing mount that gives an EQ8 a run for its money!

Check out how your mount compares in our performance charts.

Our tuning methodology provides a more detailed approach, using higher performance lubricants that help the mount perform better, which have been tested extensively over several years. 
We also clean up the castings and can upgrade the worm-gear bearings for a better drive response.


If required, we can also upgrade the main DEC and RA axis bearings as an option, but  this is rarely needed if the mount is new, as they only rotate 180º. We also load test the mount and take sound profiles, as well as stripdown/rebuild photos and video as part of the tune-up record.

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Celestron CGem Tuning Notes:

The CGem mount typically runs at 20-50 arcsecs from new unguided in independent tests. Once tuned our mounts run circa 4-6 arcsecs, and circa 0.5-1.0 arcsecs guided is often reported by our customers. In PHD2, your hypertuned mount is up to twice as responsive to guide commands. Backlash is virtually eliminated, which also improves pointing accuracy. The CGem has a specific customised build called v6.3.2C which generates the NEQ6 as a benchmark for all our mounts, a providing consistent level of engineering across the range in this Build Type.

Our latest DarkFrame Generation Tuned EQ6/NEQ6-AZ EQ6 GT mounts typically run at a Peak-to-Peak Period Error of circa ±8 ArcSec), which is 3-4x better from factory spec. Guided, all our mounts are now sub-arcsecond capable under PHD2, running typically 0.5 arc-seconds RMS, with a guided PE of ±1.5 arc-seconds, depending on seeing. This is proven Customer supplied data across several mounts, not a factory test.

The worm-gear shaft just spins with upgraded low-friction SKF bearings compared to the standard bearings, and even better still with our new Hybrid Ceramic bearings. These reduce the end-float, and provide a very solid feel to the mount, which in turn virtually eliminates the well known rocking motion in both RA/DEC. We calibrate the end-float to an accuracy of 0.01mm, to ensure a consistent dial-out of backlash and minimised play in the gear-train. 

Cleanup and de-burring of the castings is often needed as they are quite rough in places, and the mating surfaces contribute to better engagement of the worm-gear. We don't often change the main axis bearings, but we test them and replace if not smooth. These only move 180º over the course of an evening, so replacing them with ones tested to 20,000rpm is largely academic! :)

Once tuned, 10-15min subs are more than possible with this mount with very few if any lost frames. 30 minute exposures is near the mechanical limit but is achievable with lighter OTA setups with this mount without substantial re-engineering of the mount or the worm gears. This is currently under research and development. 

The AVX is better engineered, and tests have shown this to run up to 40 mins but is largely unwarranted the UK, unless you're narrowband imaging, or running long focal lengths. Check out our testimonials page, for examples of our work.

Celestron Performance:

Upgrading the worm gear bearings to Hybrid-ceramic items and belt-driving the motors substantially reduces backlash and improves periodic error. Tuned mounts run typically at circa 5-6 arcseconds RMS, and can be autoguided to consistently perform sub-arcsecond tracking with practice, especially when allied to a QHY Polemaster, and well driven via PHD2. We will advise you of the new settings as a basis to get the most out of your rebuilt mount.

We have CG-5-GT, AVX and CGem Reference mounts that are utilised to constantly improve our Zero Drop Frame tuning methodology, and demonstrate the benefits of enhancing the mount. That's the point, you can do more imaging with our mounts.

Here is a customer supplied PHD graph of one of our EQ6 Mounts. Other customer supplied examples are available upon request, and we will be updating them with Celestron versions as they become median values.

Work includes:

Each Celestron EQ Mount is examined externally for any damage and owners are notified for any extra-parts if needed. We photograph dis-assembly and reassembly of key components, and video before and after with a sound check that creates a unique sound signature for each mount. A unique report is available for an extra charge.


The Mount is stripped back in both axis to component level, inspected for damage or wear, and degreased. Owners are notified if any extra-parts are required or upgraded by request.

Axis bearings are degreased, checked for wear/damage and ultrasonically cleaned and re-lubricated, as are the bearing cone surfaces checked and cleaned in the mount. The Crowns are StellarDrive™ reprocessed to reduce friction in the casting, and to promote smooth running. We do not use sandpaper on brass, or endorse it's use in any of our mounts!

All external threaded bolts on mount and tripod (if supplied) are degreased, ultrasonically cleaned and re-lubricated. 

Mount is reassembled using upgraded greases and oils which operate in all temperatures from -25ºC to +50ºC (we use them in our Export Service and our own products so have been tested at these temperatures!). 


The Mount is then bench tested and adjusted to dial out backlash and to ensure operation of mount, for 4-6 hours to bed the mount in, then checked again prior to boxing for dispatch.

GoTo Handset and Mount is checked for Firmware updates and updated with latest code as required and tested for operation.

In the case of axis repairs and tuning we carry out a load test on every mount with either an 8 inch reflector or 100mm f9 refractor - or 70mm refractor for smaller mounts. Worm backlash is then dialled out as much movement a possible so to ensure the mount is performing as it should under real-world conditions. 

The mount is videoed/photographed during evaluation, disassembly and rebuild - for own own use only, with a soundwave check to confirm drivetrain signature.  All work carried out is now covered by our 24 month limited warranty.


E&OE - Mount Build Specification and components used subject to change without notice. Example EQ mount tracking performance is not guaranteed, and is subject to the age and condition of the Donor Mount.