Hubble Optics Dobson telescope N 508/1880 UL20 f/3.7 Premium Ultra Light DOB (53628)

Ultra-Light 20-Inch Telescope Designed for Maximum Portability

The Hubble Optics UL20 is a high-quality, large-aperture telescope engineered into an exceptionally light and compact design. Built for serious observers, it remains easy for one person to transport to dark-sky locations. Weighing only 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 back of a vehicle. It delivers breathtaking views of the night sky and offers a lifetime of rewarding observing experiences.

True 20-Inch Optical Surface

The UL20 features a parabolic primary mirror with a full 20-inch optical surface and an overall diameter of 20.4 inches. Unlike mirrors cut from a 20-inch blank with heavy beveling and reduced usable area, this design provides about 4% more effective optical surface 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 pointed at the zenith, the eyepiece is only about 69 inches above the ground. The result is spectacular views across the entire sky without ladders or uncomfortable observing positions.

Two Optical Configurations Available

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

Advantages of f/4.2

• Sharper images with nearly 50% less coma compared to 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 provide excellent visual performance. A coma corrector is required for the f/3.7 version. 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 allows rapid cooling and exceptional structural rigidity. This technology, proven in research environments and advanced amateur telescopes, minimizes “mirror seeing” by allowing the mirror to reach thermal equilibrium quickly, resulting in sharp and stable images.

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

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

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

• Linear Drive Crayford Focuser
  The precision linear-bearing Crayford focuser offers zero backlash and extremely smooth operation. It easily supports heavy modern eyepieces and accessories. A 1:10 fine-focus control allows precise focusing for high-power visual observing.

Optical Quality Assurance

Every UL20 telescope is delivered with a Foucault test report for the finished primary mirror, documenting its optical quality.

Technical Specifications

Optical System

• Design: Newtonian reflector

• Aperture: 508 mm

• Focal length: 1880 mm

• Focal ratio: f/3.7

• Resolving power: 0.23 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: 1880 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