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Explore Scientific Ultra Light Dobson 20" f/3.6


Quick Overview

Special Offer: get the Revelation Observer's Eyepiece Kit worth £124 FREE when you order this telescope!  Offer available while stocks last.

The Explore Scientific Ultra Light Dobson 20" f/3.6 GENERATION II is the largest of Explore Scientific's Dobsonians - offering enormous light gathering power in a comparatively portable package. If you're looking for a telescope that will actually delivery the types of deep sky views you've been dreaming of, without the necessity for permanent observatory mounting - then the Explore Scientific Ultra Light Dobson 20" f/3.6 GENERATION II could be for you.

Despite its large aperture the Explore Scientific Ultra Light Dobson 20" f/3.6 GENERATION II can be transported easily in small cars and is assembled within minutes without tools. The construction was optimized for maximum rigidity with a minimum of mass. The combination of big altitude wheels and an optimized aluminium-sandwich construction allows for small movements even at high magnifications. The focus position is already positioned to accept Explore Scientific's Coma Corrector (part No. 0510330), making it the ideal workhorse for the deep-sky enthusiast. A telescope with a 20-inch/ 500mm aperture gathers more than 5100-times more light than the naked eye. Details on planetary surfaces stand out even to unexperienced observers and countless deep-sky objects show details and traces of color. Bright globular clusters are resolved down to the core and the view of the lunar terminator will provide a unforgettable experience.

Both the fast 20" f3.6 main mirror and the large 120mm secondary mirror are made of high quality quartz material, which means cooling time is reduced to a minimum and the Dobsonian is quickly ready for use. Every main mirror is delivered with an individual optical test certificate, which guarantees the highest quality. A laser engraved center mark of the main mirror allows easy adjustment of collimation. The optical surface has a high-quality aluminum silvering with 94% reflectivity and an extremely resistant quartz protection layer. This overcoat allows the mirror to overcome frequently occurring fogging and dew residue cleanups without any fear of damaging the surface and guarantees a long service life.

A complete redesign of this Dobsonian was necessary to ensure the significantly increased requirements to stiffness and load bearing capacity of the optical components. All connections of the tube structure were made in the TIG welding process and no rivets and screws were used. This has made it possible for us to produce this 20" light weight Dobsonian so unbelievably stiff in spite of the low weight - a noticeably good quality which is searching for its match. The production of almost all mechanical components is carried out by our partners in Hungary and the final assembly of the optics and subsequent quality control takes place in Rhede, Germany.

The design and equipment specifications of the smaller Dobsonian models, which have on the market for years now, have been used as a basis for this design. First of all, of course, very easy deconstruction/reconstruction and transportability are paramount. Set-up and dismantling can be carried out without tools. The main and secondary mirrors are adjustable during the observation and only two adjusting screws have to be moved. Thanks to the use of precision ball-heads in the main mirror cell and a precision hinge for secondary mirror suppport, the adjustment is absolutely easy and guarantees excellent stability. All connecting parts of the tube trusses now consist of CNC machined aluminum and are attached by stainless steel dowel screws. The secondary mirror can now also be adjusted by the adjusting screws in the direction of the optical axis. The tried and tested 2.5 HEXAFOC focuser with 1:10 fine adjustment has been used for years - this allows vignetting-free observation despite the fast aperture ratio. A second 40° displaced installed mounting plate with a viewfinder shoe allows the rotation of the tube top in combination with a favorable position of the viewfinder tube, or the mounting of an additional TELRAD viewfinder. The 6 supporting feet underneath the rockerbox offer a perfect stability and guarantee a smooth tracking in azimuth. Four smaller fans are installed in the side of the mirror box, as well as a large fan installed under the main mirror. This allows an even quicker adaptation to the ambient temperature and reduces the tube seeing (boundary layer removal). The lateral altitude wheels can now be stowed comfortably in the foam layers of the mirror box.

Last but not least another plus point: the optical tube and the mirror cell are designed to be also used on heavy equatorial mounts.

Dimensions for mobile use:

DIMS total: 680x680x1790mm; Rockerbox 678mmx678mmx347mm; Mirrorbox 590mmx590mmx361mm; Trusses approx. 1084mm; Truss diameter: 25mm; Eyepiece height while pointing at zenith approximately 1,63m; 20“ Total net weight: 53 kg; 20“ Mirror Box + Altitude wheels: 35,8kg; 20“ Secondary Cage: 3,8kg; Rockerbox: 10,6 kg; 20“ 4 Truss pairs: 2,8kg; 20“ Primary mirror: 20kg

IMPORTANT NOTE: All current product pictures are showing the prototype. Many hints from our customers have pushed us to make some additional changes which will require some updates.


Truss-Dobsonian telescope in full Aluminium construction
Handcrafted in HUNGARY and GERMANY
Fast 20" f3.6 optics with 1800mm focal length
Large 120mm secondary mirror (short axis)
Quarz primary- and secondary mirror set
Laser engraved central mark on primary mirror
Eyepiece height while pointing at zenith approximately 1,63m
Full welded rigid telescope structure - no rivets and no screws
Telescope tube and rockerbox powder-coated
Collimation while observing with the delivered tooling
DeLuxe 2,5" HEXAFOC focuser with 1:10 gear-reduction
8x50 finder scope with red illuminated reticle
Slider bearings made from TEFLON und GRP for smooth and precise movement
Improved primary mirror cell with completely redesigned mechanics
High precision hinge system for secondary mirror holder
Secondary mirror holder with adjustment mechnism along the optical axis
6 larger feet to improve stability
Counter-weights (2 x 1.0 kg) included
2 universal finder slots to enable an easy finder position
Quick-lock fasteners with new springloaded design for comfortable use
Large powder-coated yellow altitude wheels for smooth tracking
Altitude wheels can be stored in the mirror box
5 cooling fans are speeding up the cool-down time


Truss Dobsonian Telescope
Individual optical test report for primary mirror
8x50 finder with red illuminated reticle
Stray light shield for secondary cage
Primary mirror collimation tool
Battery compartment with bag for fans
Extension tube for focuser
Reducer 2"/1.25"

Only 0 left

Availability: Out of stock


Field of application
Field of application

  • Deep Sky Observation

  • Planetary observation

Focus group
Focus Group

  • Advanced Amateurs

  • Specialists and Research

  • Visual enthusiasts

Product family
Product Family Reflector telescope
Optical design Newtonian Reflector
Magnification from 40
Maximum recommended magnification 1000
Material Primary mirror Quartz
Primary mirror diameter 500 mm
Material Secondary mirror Quartz
Secondary mirror diameter 120 mm
Focal length 1800 mm
Aperture ratio 3.6
Angular resolution 0.28 arc seconds
Finderscope 8 x 50 mm - illuminated
Mount Type Dobson
Batteries needed2 2x LR41, 1.5V
Batteries included
Material OTA Aluminium
Bearing in alt-azimuth / RA Teflon
Bearing in elevation / DEC Teflon
Focusing system 2.5" Hexafoc DeLuxe with 10:1
Colour black
Standard warranty 2
Ext. warranty after online registration 5 Years
Total length 68 cm
Total width 68 cm
Total height 179 cm
Net Weight total (incl. accessories) 53 kg
Eyepiece Barrel Diameter 50.8 mm

PLEASE NOTE: due to mechanical and optical checks made on each unit before shipping, timespan from placement of order, to delivery, is in the region of 1-2 weeks.

SHIPPING DIMENSION - truck shipment only in order to guarantee a safe transport: 

BOX1: 600x600x380 approx. 44 kg ; BOX2: 690x690x330 approx. 17 kg ; BOX3: 150x150x1150 approx. 4 kg

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