The Explore Scientific 20-inch f/3.6 Truss-Tube Dobsonian is the telescope that seasoned observers save up for — a 500mm fast-cooling quartz primary mirror that gathers over 5,100× more light than the naked eye, packaged in a TIG-welded truss-tube structure that actually fits in a vehicle. The f/3.6 focal ratio is ferociously fast: wide, bright fields of view and a view of the night sky that puts faint nebulae and remote galaxies on a completely different level compared to anything under 16 inches.
The integrated fan system pairs with the open truss-tube design to bring 20 inches of glass to thermal equilibrium quickly — critical at this aperture because a mirror still cooling produces turbulent air that blurs fine detail. The 2.5" dual-speed HEX rack-and-pinion focuser handles any eyepiece combination without flex, and the rocker-box mount rolls smoothly on its bearings so one-handed tracking feels natural even at high power.
What you'll see:
- Galaxies — spiral arm detail, dust lanes, HII regions, and satellite galaxies in nearby systems
- Globular clusters — a snow-globe of individual stars resolved all the way to the very core
- Faint galaxy clusters — multiple members of the Virgo, Coma, and Fornax clusters visible simultaneously
- Planetary nebulae — complex shell structure, colour gradients, and the central white dwarf
- Dark nebulae — dark molecular clouds silhouetted against star-rich Milky Way fields
What's in the box:
- 500mm (20") fast-cooling quartz primary mirror — the telescope's light-collecting heart
- Secondary mirror assembly — redirects focused light to the eyepiece
- TIG-welded truss-tube poles and hardware — rigid, lightweight structural skeleton
- Dobsonian rocker box base — smooth altitude and azimuth bearings for alt-az tracking
- 2.5" dual-speed HEX rack-and-pinion focuser — stable, 10:1 fine focus ratio
- Integrated radial mirror fans — speed thermal equilibration of the large primary mirror
- Red-dot LED finder — helps you navigate to targets before zooming in
- Collimation assist tool and soft-light baffle — included accessories
Beginner note: A 20-inch Dobsonian rewards planning — you'll want dark skies, a selection of eyepieces for different magnifications, and a step stool for zenith objects. Collimation is required each session (mirrors must be aligned after assembly), but the included collimation tool makes it manageable. The payoff is a view of the universe that very few people ever experience.
Specs:
| Aperture |
500mm (20") — collects ~5,100× more light than the naked eye |
| Focal Length |
1,826mm — reach for both detailed galaxy views and wide deep-sky fields |
| Focal Ratio |
f/3.6 — extremely fast; very wide, bright views at low power |
| Optical Design |
Newtonian reflector — fast-cooling quartz optics, truss-tube Dobsonian |
| Focuser |
2.5" dual-speed HEX rack-and-pinion — 10:1 fine focus, handles heavy accessories |
| Cooling System |
Integrated radial fans + open truss-tube design — fast thermal equilibrium |
| Secondary Mirror Obstruction |
24% — minimal impact on contrast |
| Mount |
Dobsonian rocker box — smooth alt-az bearings, stable for manual tracking |
For observers who want the ultimate visual deep-sky experience in a transportable package, the Explore Scientific 20" Dobsonian is the scope that ends the aperture search.
