Sky-Watcher Stargate 20" f/3.9 Truss-Tube AZ Dobsonian Telescope

Sky-Watcher Stargate 20" f/3.9 Truss-Tube AZ Dobsonian Telescope

Sky-Watcher Stargate 20" f/3.9 Truss-Tube AZ Dobsonian Telescope

B&H # SK20STTD MFR # S11910

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Special Order
Expected availability: 7-14 business days

Product Highlights

  • Large 20" (508mm) Aperture
  • 2000mm Focal Length, f/3.9 Focal Ratio
  • Fused Borosilicate Primary Mirror
  • 2" Two-Speed Crayford-Style Focuser
  • Floor-Standing Manual Alt-Az Mount
  • 10mm, 28mm, Collimation Eyepieces
  • Large 9x50 Finder with Bracket
  • Three 2.3-pound (1kg) Counterweights
  • Easy-to-Manage Open Truss-Tube Design
  • Ribbed Fabric Truss Shroud
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Aperture: 20" f/3.9

18" f/4.2

Special Order

20" f/3.9 Stargate 20" f/3.9

Not available with current selections

Mount: Manual Alt-Az

Manual Alt-Az GoTo Alt-Az

Not available with current selections

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Price: $6,999.00

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Sky-Watcher Stargate overview

  • 1Description

With the largest light bucket in the series, the Sky-Watcher Stargate 20" f/3.9 Truss-Tube Dobsonian Telescope gives users exceptional performance with a low dollar-to-aperture cost. Proprietary aluminum mirror coatings ensure maximum reflectivity, and a fused conical parabolic primary mirror design allows for thinner mirror construction. This provides faster cooling and lighter weight while also correcting spherical aberration to eliminate distortion across the entire field of view, especially at the edges.

This telescope's large 20" aperture draws in a tremendous amount of light to reveal awe-inspiring details of the Moon and planets. Deep-sky objects will be visible even for inexperienced observers and bright star clusters can be resolved to their core. Its f/3.9 focal ratio and dual-speed Crayford focuser makes this an ideal choice for imaging. The fast focal ratio enables devices to capture images in less time than slower scopes, while the focusing mechanism gives it the ability to achieve tack-sharp focusing with zero backlash that rack-and-pinion focusers are generally unable to accomplish. This 2" focuser will accept larger eyepieces so users can enjoy a truly immersive visual experience and will ensure larger imaging sensors are completely covered.

Its truss-tube construction and simple assembly enable a virtually complete breakdown for easier transportation and storage, with an assembly time of less than 20 minutes. To help block stray peripheral light and internal reflected light, Sky-Watcher includes a ribbed fabric shroud that completely covers the open trusses, giving users the convenience of the truss system with the performance of traditional solid tubes. The rocker box weighs in at 70 pounds and provides a rock-steady observational platform with very low vibration.

Optical Tube
  • 20" (508mm) aperture
  • f/3.9 focal ratio
  • 2000mm effective focal length
  • Dobsonian reflector light path
  • Fused borosilicate mirror glass allows for thinner mirrors that reduce weight and increase cooling
  • Highly reflective aluminum mirror coatings
  • 134mm secondary mirror, 7% obstruction by area
  • Resolution: 0.28 (Rayleigh); 0.23 (Dawes)
  • Dual-speed Crayford-style focuser enables more precise focusing than conventional rack-and-pinion without backlash
  • Max eyepiece height: 79" (200.7 cm), when OTA is pointed at the zenith
  • Open truss tube design allows for easier breakdown and transportation, with reduced weight versus solid tubes
  • Manual alt-azimuth
  • Steel and Teflon azimuth and altitude bearings enable smooth movement with limited vibrations
  • Floor standing with adjustable feet for proper leveling
  • Included three 2.3-pound (1kg) counterweights enable precise balancing, especially when using accessories such as heavy eyepieces or imaging rigs
  • Weight: 138 pounds, fully assembled with counterweights
Included Accessories
  • 1.25" 10mm eyepiece yields 200x power, accepts most 1.25" astronomical filters
  • 2" long eye relief 28mm eyepiece produces 71x magnification, accepts most 2" astronomical filters
  • 1.25" collimation eyepiece enables the user to properly collimate the primary and secondary mirrors
  • 2"-to-1.25" reducer adapter allows the use of smaller eyepieces and accessories in the larger drawtube
  • 9x magnification ensures a wide field of view for faster alignment and easier star-hopping navigation
  • Large 50mm objective enables it to resolve dimmer objects
  • Covers the open portion of the truss assembly
  • Ribbed fabric absorbs internal reflected light
  • Blocks peripheral exterior and reflected interior light which can interfere with light transmission to the mirrors
  • Helps to produce higher contrast views and sharper images during astrophotography
In the Box
Sky-Watcher Stargate 20" f/3.9 Truss-Tube AZ Dobsonian Telescope
  • 9x50 Finderscope
  • 2" 28mm Eyepiece
  • 1.25" 10mm Eyepiece
  • 1.25" Collimation Eyepiece
  • Eyepiece Reducer Adapter
  • Ribbed Fabric Shroud
  • 3 x 2.3-lb Counterweights
  • Limited 2-Year Warranty
  • Table of Contents
    • 1Description

    Sky-Watcher Stargate specs

    Optical Design Dobsonian reflector
    Aperture 20.0" / 508.0mm
    Focal Length 2000 mm
    Focal Ratio f/3.94
    Eyepiece Barrel Diameter 2"
    1.25" with included adapter
    Diagonal None
    Finderscope 9 x 50
    Tripod None
    Mount Type Floor-mounted manual alt-az
    Power Source None
    Optical Tube Dimensions Height: 82.7" / 210.0 cm
    Horizontal radius: 59.1" / 150.0 cm
    Base diameter: 23.2" / 59.0 cm
    Weight Upper Cage: 12.0 lb / 5.7 kg
    Truss Poles: 16.0 lb / 7.3 kg, total; 2.6 lb / 1.2 kg, each
    Mirror Box: 70.0 lb / 31.8 kg
    Dobsonian Base: 40.0 lb / 18.1 kg
    Fully Assembled: 138.0 lb / 62.6 kg, with weights

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