Hubble Optics Dobson telescope N 508/1676 UL20 f/3.3 Premium Ultra Light DOB (87499)

Ultra-Light 20-Inch Telescope for Extreme Portability

The Hubble Optics UL20 is a high-quality, large-aperture telescope engineered into a remarkably light and compact design. Built for serious observers, it remains easy for a single person to transport to dark-sky locations. Weighing about 90 pounds, it is roughly one third the weight of a traditional Dobsonian of similar size and folds into a compact package that fits into almost any car.

This is the telescope you will actually take out and use often—whether from the garage or the trunk—delivering stunning views of the night sky and a lifetime of observing enjoyment.

Premium Optics with a True 20-Inch Light-Gathering Surface

The UL20 features a parabolic primary mirror with a full 20-inch optical surface and a generous 20.4-inch overall diameter. Unlike mirrors made from a beveled 20-inch blank with a smaller effective surface, this design provides about 4% more usable optical area and light-gathering power than most other 20-inch telescopes on the market.

Thanks to its fast focal ratio, the eyepiece position is almost always reachable while standing flat-footed. When aimed at the zenith, the eyepiece height is only about 69 inches above the ground. The result is spectacular views across the entire sky without ladders or awkward positions.

Two Optical Configurations

The UL20 is available in two focal ratios: f/3.7 and f/4.2.

Advantages of f/4.2

• Sharper images with nearly 50% less coma than the f/3.7 version

• Smaller central obstruction

• Easier to achieve precise collimation

Advantages of f/3.7

• No ladder required for most observers

• Wider field of view

Both versions deliver excellent visual performance. A coma corrector is required for the f/3.7 configuration. Please note that the f/4.2 version requires additional counterweight at the bottom (physical or spring-based), which is not included.

Key Design Features

• Sandwich Mirror Technology
  The open-core sandwich mirror design promotes rapid thermal equilibrium and exceptional structural strength. This technology, proven in research environments and advanced amateur instruments, minimizes “mirror seeing” by allowing the mirror to cool quickly, resulting in stable, sharp images.

• Semi-Enhanced Optical Coatings
  The primary mirror uses a 92% semi-enhanced reflective coating with a precision dielectric overcoat for maximum reflectivity and long-term protection. The secondary mirror features a 96% enhanced coating, ensuring excellent brightness and contrast.

• Engineered Mirror Support System
  A carefully modeled flotation and support system provides optimal support for the primary mirror. The independent three-point collimation system eliminates astigmatism commonly caused by sling-based supports pulling on the mirror edge during adjustment.

• All-Metal Construction
  The telescope structure is designed using advanced CAD and finite element analysis for maximum rigidity and stability. CNC-machined components, strong aluminum alloy truss tubes, a steel mirror cell, and a durable powder-coated finish combine strength with refined appearance.

• Linear Drive Crayford Focuser
  The precision linear-bearing Crayford focuser offers zero backlash and extremely smooth operation. It easily supports heavy modern eyepieces and imaging accessories. A 1:10 fine-focus control allows critical focusing at high magnifications or during imaging.

Optical Testing and Quality Assurance

Each UL20 primary mirror is delivered with a Foucault test report, documenting the optical quality of the finished mirror.

Technical Specifications

Optical System

• Design: Newtonian reflector

• Aperture: 508 mm

• Focal length: 1676 mm

• Focal ratio: f/3.3

• Resolving power: 0.27 arcseconds

• Limiting magnitude: 15.3

• Light-gathering power: 5270×

• Maximum useful magnification: 1016×

Optical Tube Assembly

• Truss tube construction

• Tube material: Aluminum

• Tube weight: 35 kg

Primary Mirror

• Shape: Parabolic

• Optical quality: 1/10 wave

• Material: Pyrex glass

• Reflectivity: 92%

• Adjustable collimation: Yes

Secondary Mirror

• Diameter: 100 mm

• Central obstruction: 19.7%

Focuser

• Type: Crayford

• Fine focus reduction: 1:10

• Eyepiece connection: 2 inch

• Focusing travel: 50 mm

Mount

• Type: Dobsonian

• GoTo capability: No

Included Accessories

• Finder: Red-dot finder

• Optical test report: Included

• Eyepieces: Not included

General Information

• Total weight: 40 kg

• Eyepiece height at zenith: 1490 mm

• Series: Ultra Light

Recommended Use

• Moon and planets: Yes

• Nebulae and galaxies: Yes

• Astrophotography: Not recommended

• Nature observation: No

• Solar observation: No

User Level

• Beginners: No

• Advanced observers: Yes

• Observatory use: No