UL20g 20" Premium Ultra Light GoTo Dobsonian Telescope

UL20g 20" Premium Ultra Light GoTo Dobsonian Telescope

f/4.2: $7,195

f/3.7: $7,995

f/3.3: $8,895

F/# Deposit (50% of the base system)

Choose your f/#
  • A quantum leap in optical performance - the UL20g Truss Dobsonian telescope's huge 20" diameter primary mirror gathers more than 6 times more light than popular 8" reflectors or almost three times of the light grasp of a 12" telescope
  • A Premium, Light, Compact and Portable Design - About half the weight of traditional Dobsonian telescopes
  • Preinstalled with the state of art Onstep GoTo controller designed by Howard Dutton (wwww.stellarjourney.com).


UL20g Specs

  • Optical diameter:508mm
  • Focal length : ~1676mm (f/3.3), ~1880mm (f/3.7), ~2134mm (f/4.2)
  • Eyepiece height at zenith: ~1490mm(~59 in, f/3.3), 1745mm (~69 in, f/3.7), 2000mm (~79 in, f/4.2)
  • Optics type: Parabolic
  • Eyepieces: Not included
  • Optical quality: Diffraction limited++ (Strehl 0.95+ for the primary mirror, 1/10 lambda or better in PV for the secondary mirror)
  • Finder scope: Not included
  • Focuser: 2" dual-speed linear bearing Crayford
  • Secondary mirror obstruction: 100 mm (f/3.3, f/3.7), 90mm (f/4.2)
  • Secondary mirror obstruction by diameter: 19.7% (f/3.3, f/3.7), 17.7 (f/4.2)
  • Secondary mirror obstruction by area: 3.9% (f/3.3, f/3.7), 3.1% (f/4.2)
  • Mirror coatings/over-coatings: 96% Enhanced coating on both of the primary and secondary mirrors
  • Tube material: 6063-T6 Aluminum Alloy tubes with black zinc plated steel knob screws; Aluminum Alloy main structure (OTA and mount) and structure steel mirror cell.
  • Length of optical tube : 73 in (f/3.3, f/3.7), 83 in (f/4.2)
  • Weight, optical tube : 76 lbs (f/3.3,f/3.7), 77 lbs (f/4.2)
  • Weight, fully assembled : ~99 lbs. (f/3.3, f/3.7), ~100 lbs (f/4.2)
  • State-of-art GoTo with Built in WiFi and Bluetooth
  • Power Supply: 12-15V 2A, 5.5-2.1mm center positive
  • Dawes Limit(arcsec): 0.23
  • Rayleigh Limit(arcsec): 0.27
  • Limiting Mag: 16.0
  • Maximum Magnification: 1000
  • Additional, optional accessories: 8x50 Finder, Shroud, Wheelbarrow, Vinyl foam Cushioned Grips
  • Other features: Sling lateral support and deluxe push-pull brass knob collimation screws

Features of the UL20g:

Exclusive Sandwich Mirror Technology:

Our sandwich mirror technology has been used to manufacture research-grade optical elements and proven by over a half dozen years of successful applications at research facilities such as NASA, California State Polytechnic University San Luis Obispo, for the US Army, and in amateur telescopes around the world. Hubble sandwich mirror’s open core and close back design not only allows air to circulate through the mirror, but also provide the maximum structure strength to allow a simpler mirror cell design. Our sandwich mirror will reach thermal equilibrium up to 10 times faster than a traditional solid mirror and means the mirror can deliver great views even as the air around the telescope is changing temperature.

Why is thermal equilibrium so critical? The main issue is "mirror seeing," the turbulence seen through the eyepiece of the telescope when the air above the mirror is different from the mirror itself. Since a sandwich mirror cools far more rapidly than a solid mirror of the same thickness, this major source of distortion is eliminated quickly, giving you sharp and stable views. With ever- changing temperatures during observing or imaging, your thick and solid mirror may never reach equilibrium, and never reach its full optical potential. This is one of the major reasons why our lightweight-sandwich mirror has superior optical performance in real world situations, even without an active cooling system. (Active cooling systems, such as fans, introduce their own problems, such as micro vibration, which may seriously degrade the image quality.) Our sandwich mirrors reach equilibrium extremely fast, and without any external disturbing aid.

The state of art OnStep GoTo controller is extremely powerful and feature rich. The Hubble OnStep GoTo controller supports:

  • The INDI Drivers to use with CdC, KStars, and Ekos.
  • ASCOM drivers with IP and Serial support under the LX200 protocol.
  • WiFi 802.11n /g/n connection with built-in website accessible from any browser from any platform and the direct WiFi support for the Sky Safari and Stellarium
  • Bluetooth classic 4.2 support to host computer for the ASCOM connection and the direct wireless support to Sky Safari & Stellarium
  • iOS App and Android Virtual Handpad Apps to control the scope with initialization, configuration, alignment, and movement (Slewing and GoTo).
  • Smart Hand Controller with about 30,000 objects. You can fully control the scope with initialization, configuration, alignment, and movement control (Slewing and GoTo) with this Hand Controller
  • The Telescope Encoders for the extra accuracy in pointing and tracking
  • Real Time Clock (RTC): The RTC module maintains seconds, minutes, hours, day, date, month, and year information.
  • Advanced 1-9 star alignment; 3 stars alignment usually gives good results and is less difficult to do
  • Park/Unpark function
  • Sideral/Lunar/Solar tracking rates
  • Spiral Search
  • Manual speed/guide speed rates:0.5x, 1x, 2x, 8x, 20x, 48x, 0.5 Max, Max (2dps)
  • Slewing Rates: 48x, Max (2dps, default), 2*Max (4dps)

Enhanced Optical Coatings:

The Hubble UL20g primary mirror and the secondary mirror are coated with the state of the art 96% Enhanced optical coatings to assure it collects as many (while scattering as little) photons as possible to focus it into a bright and contrast-rich image. The optimal 96% Enhanced coating has multiple over-coating of precision controlled dielectric layers to maximize the reflectivity and provide excellent chemical and mechanical protection for the mirror coating.

A Real Mirror Cell In A Real Mirror Box:

The UL20g has an extensively modeled and optimized 18-point flotation system that provides more than adequate support for the sandwich mirror. The three-point Push-Pull collimation system is completely independent from the sling lateral support. It will totally eliminate the often-found potato chip astigmatism introduced by sling belt when using the simple 3 pivoted bolts collimation system. In a simple pivoted bolts collimation system, the collimation of the primary mirror may cause the sling belt to pull the mirror axially on the mirror edge, bending the mirror to a potato-chip shape, causing annoying astigmatism. It also comes with a real mirror box for easy and safe mirror protection and transportation.

All Metal Construction:

The UL20g mechanical structures have been extensively modeled via 3D CAD and advanced FEA to provide the optimal structure strength and stability. Machined with Computer Numerical Control (CNC) technology and hand fitted to assure proper fit and finish. Super strong T6063-T3 aluminum alloy truss tubes, structure steel mirror cell and aluminum alloy OTA and mount structure. Completed with deluxe and environmentally friendly black powder coating, it is such a pleasure to look at, not to mention the enjoyment to look through.

Dual-Speed 2-inch Linear Drive Crayford Focuser:

The Hubble UL20g comes with a precision dual-speed, 2-inch diameter focuser. It's a beautiful piece of precision machining that enhances the viewing experience as well as the overall impression of a premium quality instrument you'll have with this telescope. This focuser is robust! It is a zero-backlash "Crayford-style" design further enhanced with modern "linear bearings" meaning you get a rock-solid, super smooth focusing experience that can handle the weight of even the heaviest of modern eyepieces. Its tension, the pressure on the drawtube, is preset to a very reasonable level, but adjustable to lock heavy equipment in place if desired. The smaller stainless steel focus control adjusts focus at a rate 8 times finer than the larger focus wheels. This fine adjustment allows for critical focusing during high power visual observing or for imaging applications. The focuser has 50mm of travel distance.

Should I choose the f/3.3, f/3.7 or f/4.2?

Advantages of f/4.2:

  • Sharper images. It has almost 50% less coma than UL20 f/3.7; a coma corrector will still be helpful, but many people may live without it.
  • With the special introduction offer, you save $1,300 over UL f/3.7!
  • Smaller central obstruction, 3.5” (f/4.2) v.s. 4.0” (f/3.7) secondary mirror
  • Easier to achieve perfect collimation

Advantages of f/3.3 and f/3.7:

  • No ladder is needed for f/3.3 at all; while you may need one-step ladder for an f/4.2 when close to zenith direction.
  • Wider FOV for f/4.2, and even wider with f/3.3!

The f/3.3, f/3.7 and f/4.2 will all provide you with excellent views. A coma corrector is recommended for the UL20 f/3.3.

With our unique two-section truss tubes for f/4.2 (one section truss for f/3.3 and f/3.7), f/4.2 is just as portable and strong as f/3.3 and f/3.7. At the end, it is really your personal preference. Please note that some counter weight (real and/or a virtual spring counter weight) will be required for f/4.2 at the bottom(and for f/3.3 at the top), which is NOT provided

Instructions Manual

Click here for the UL20g Setup instructions manual PDF.

Click here for the GoTo instructions manual PDF


Click here for the UL20 dimensions when folded.

Order and Shipping Info

There's a 50% deposit for the base system, and the full payment for the optional accessories at the order time, the rest including shipping will be paid before the delivery (about 60 days after the deposit) via a Paypal invoice.

Please note that the 60 days delivery is the estimated production lead time which does not include shipping transit time.

We offer very reasonable worldwide shipping costs (at least for most of the countries) for the total system. The Economy shipping is no longer available.

UL20g will be shipped in 4 boxes: the main structure 1 & 2, the truss tubes, and the primary mirror.

Country Economy(US$) Regular(US$)
US NA 995
US(Hawaii) NA 1062
Austria NA 894
Australia NA 965
Belgium NA 940
Brazil NA 2950(*)
Canada NA 915
Chile NA 1450
Denmark NA 850
France NA 875
Germany NA 860
Israel NA Contact Us(*)
Italy NA 910
Japan NA 590
Korea, South NA 565
Lithuania NA 1980
Mexico NA 1065
Netherlands NA 795
New Zealand NA 920
Norway NA 845
Portugal NA 965
Philippines NA 450
Poland NA Contact Us(*)
Romania NA 955
Russia NA 1495
Singapore NA 476
South Africa NA 1700
Spain NA Contact Us(*)
Sweden NA 830
Switzerland NA 860
Taiwan NA 510
UK NA 890

* Shipped via Fedex, the exact cost depends on your specific address.