Aperture for deep-sky observing
The 508 mm primary collects light for observing galaxies, nebulae and globular clusters. Dark skies, atmospheric conditions and careful setup determine the detail you can see.
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Hubble Optics
Hubble Optics UL20 20 Inch Premium Ultra Light Dobsonian Telescope
$10,690.00
20-inch aperture. Three focal ratios, three ways to point.
The Hubble Optics UL20 is a 508 mm parabolic reflector for observers planning a serious large aperture visual setup. Choose f/4.2, f/3.7 or f/3.3, then Manual, Guided Push-To or Automatic Go-To control.
A ventilated sandwich mirror at the centre of the UL20.
The sandwich primary mirror has an open internal structure that promotes heat exchange. Letting the mirror approach the surrounding air temperature helps reduce the turbulence that can soften the image. Cooldown still depends on the starting temperature and observing conditions.
Official UL20 primary-mirror photograph, showing the open sandwich structure.
How the UL20 supports and focuses the image.
18-point mirror support
The flotation cell distributes the rear support of the primary mirror. Lateral support and collimation are separate, so alignment does not rely on distorting the mirror edge.
Dual-speed focusing
The 2-inch linear-bearing Crayford focuser gives you coarse adjustment followed by fine focus. Eyepieces are selected separately to suit the targets and magnifications you use.
Choose how you find and follow objects.
Manual
Locate targets yourself and move the telescope by hand.
- PointingBy hand
- Following an objectBy hand
Guided Push-To
Digital position guidance helps you locate a target; you still move the telescope yourself. Push-To does not add motorised tracking.
- PointingGuided, moved by hand
- Following an objectBy hand
Automatic Go-To
After setup and alignment, the drive moves to selected objects and follows them as the sky turns. A suitable power source is required.
- PointingMotorised
- Following an objectMotorised
These are separate Telescope Control choices. Compatible hardware and software are required for phone or tablet control. Power requirements depend on the supplied control system.
Choose focal ratio for your observing position.
The lower focal-ratio option places the eyepiece lower. The higher focal-ratio option uses a smaller secondary mirror. Each focal ratio is available with all three Telescope Control choices.
f/4.2
- Focal lengthapproximately 2134 mm
- Eyepiece at zenithapproximately 2000 mm
- Secondary diameter90 mm
f/3.7
- Focal lengthapproximately 1880 mm
- Eyepiece at zenithapproximately 1745 mm
- Secondary diameter100 mm
f/3.3
- Focal lengthapproximately 1676 mm
- Eyepiece at zenithapproximately 1490 mm
- Secondary diameter100 mm
Eyepiece heights are approximate, with the telescope pointing straight up. Your height and observing position determine whether a step is needed.
Plan the space and handling.
Assembled weight, Manualapproximately 39.9 kg (88 lb); f/4.2 approximately 40.4 kg (89 lb)
Eyepiece height at zenithf/4.2: approximately 2000 mm; f/3.7: approximately 1745 mm; f/3.3: approximately 1490 mm
Manual telescope figures exclude added control equipment and observing accessories. Plan carrying, storage and eyepiece access for your chosen configuration.
Good to know.
Choose eyepieces and finder separately
Eyepieces and a conventional optical finder are not included. Shrouds and other light-control accessories are separate options.
Check collimation after assembly
Collimation aligns the mirrors. Check it after reassembly and before observing. UL20 assembly and setup manual.
Allow for balance weights
The longer focal-ratio configuration can require additional counterweight at the lower end. Counterweights are not included.
Keep this telescope away from the Sun
Never point the telescope or finder at the Sun without the correct purpose-made solar protection. Unfiltered viewing can cause permanent eye damage.
Specifications.
Optics
Optical Design
Reflector
Optical Diameter
508mm
Focal Length
~1676mm (f/3.3), ~1880mm (f/3.7), ~2134mm (f/4.2)
Focal Ratio
f/3.3, f/3.7, f/4.2
Eyepiece Height at Zenith
f/4.2: approximately 2000 mm; f/3.7: approximately 1745 mm; f/3.3: approximately 1490 mm
Optics Type
Parabolic
Optical Quality
Diffraction limited (Strehl 0.95+, 1/10 wave PV secondary)
Focuser
2" dual-speed linear bearing Crayford
Secondary mirror diameter
f/4.2: 90 mm; f/3.7 and f/3.3: 100 mm
Structure and controls
Tube Material
6063-T6 Aluminium Alloy, structural steel mirror cell
Optical Tube Length
73" (f/3.3, f/3.7), 83" (f/4.2)
Mirror support
18-point flotation cell
Assembled weight (Manual)
approximately 39.9 kg (88 lb); f/4.2 approximately 40.4 kg (89 lb)
Eyepieces
Not included
Conventional finder scope
Not included
Telescope Control
Manual; Guided Push-To; Automatic Go-To
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20-inch aperture. Three focal ratios, three ways to point.
The Hubble Optics UL20 is a 508 mm parabolic reflector for observers planning a serious large aperture visual setup. Choose f/4.2, f/3.7 or f/3.3, then Manual, Guided Push-To or Automatic Go-To control.
A ventilated sandwich mirror at the centre of the UL20.
The sandwich primary mirror has an open internal structure that promotes heat exchange. Letting the mirror approach the surrounding air temperature helps reduce the turbulence that can soften the image. Cooldown still depends on the starting temperature and observing conditions.
Official UL20 primary-mirror photograph, showing the open sandwich structure.
How the UL20 supports and focuses the image.
Aperture for deep-sky observing
The 508 mm primary collects light for observing galaxies, nebulae and globular clusters. Dark skies, atmospheric conditions and careful setup determine the detail you can see.
18-point mirror support
The flotation cell distributes the rear support of the primary mirror. Lateral support and collimation are separate, so alignment does not rely on distorting the mirror edge.
Dual-speed focusing
The 2-inch linear-bearing Crayford focuser gives you coarse adjustment followed by fine focus. Eyepieces are selected separately to suit the targets and magnifications you use.
Choose how you find and follow objects.
Manual
Locate targets yourself and move the telescope by hand.
- PointingBy hand
- Following an objectBy hand
Guided Push-To
Digital position guidance helps you locate a target; you still move the telescope yourself. Push-To does not add motorised tracking.
- PointingGuided, moved by hand
- Following an objectBy hand
Automatic Go-To
After setup and alignment, the drive moves to selected objects and follows them as the sky turns. A suitable power source is required.
- PointingMotorised
- Following an objectMotorised
These are separate Telescope Control choices. Compatible hardware and software are required for phone or tablet control. Power requirements depend on the supplied control system.
Choose focal ratio for your observing position.
The lower focal-ratio option places the eyepiece lower. The higher focal-ratio option uses a smaller secondary mirror. Each focal ratio is available with all three Telescope Control choices.
f/4.2
- Focal lengthapproximately 2134 mm
- Eyepiece at zenithapproximately 2000 mm
- Secondary diameter90 mm
f/3.7
- Focal lengthapproximately 1880 mm
- Eyepiece at zenithapproximately 1745 mm
- Secondary diameter100 mm
f/3.3
- Focal lengthapproximately 1676 mm
- Eyepiece at zenithapproximately 1490 mm
- Secondary diameter100 mm
Eyepiece heights are approximate, with the telescope pointing straight up. Your height and observing position determine whether a step is needed.
Plan the space and handling.
Assembled weight, Manualapproximately 39.9 kg (88 lb); f/4.2 approximately 40.4 kg (89 lb)
Eyepiece height at zenithf/4.2: approximately 2000 mm; f/3.7: approximately 1745 mm; f/3.3: approximately 1490 mm
Manual telescope figures exclude added control equipment and observing accessories. Plan carrying, storage and eyepiece access for your chosen configuration.
Good to know.
Choose eyepieces and finder separately
Eyepieces and a conventional optical finder are not included. Shrouds and other light-control accessories are separate options.
Check collimation after assembly
Collimation aligns the mirrors. Check it after reassembly and before observing. UL20 assembly and setup manual.
Allow for balance weights
The longer focal-ratio configuration can require additional counterweight at the lower end. Counterweights are not included.
Keep this telescope away from the Sun
Never point the telescope or finder at the Sun without the correct purpose-made solar protection. Unfiltered viewing can cause permanent eye damage.
Specifications.
Optics
Optical Design
Reflector
Optical Diameter
508mm
Focal Length
~1676mm (f/3.3), ~1880mm (f/3.7), ~2134mm (f/4.2)
Focal Ratio
f/3.3, f/3.7, f/4.2
Eyepiece Height at Zenith
f/4.2: approximately 2000 mm; f/3.7: approximately 1745 mm; f/3.3: approximately 1490 mm
Optics Type
Parabolic
Optical Quality
Diffraction limited (Strehl 0.95+, 1/10 wave PV secondary)
Focuser
2" dual-speed linear bearing Crayford
Secondary mirror diameter
f/4.2: 90 mm; f/3.7 and f/3.3: 100 mm
Structure and controls
Tube Material
6063-T6 Aluminium Alloy, structural steel mirror cell
Optical Tube Length
73" (f/3.3, f/3.7), 83" (f/4.2)
Mirror support
18-point flotation cell
Assembled weight (Manual)
approximately 39.9 kg (88 lb); f/4.2 approximately 40.4 kg (89 lb)
Eyepieces
Not included
Conventional finder scope
Not included
Telescope Control
Manual; Guided Push-To; Automatic Go-To
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