Explore Scientific 10-inch f/5 Hybrid Truss Tube Dobsonian Telescope

The 10-inch Dobsonian for Deep-Sky Exploration

A 10-inch Dobsonian is a significant step up in aperture: a 254mm mirror collects hundreds of times as much light as the naked eye. It is a manual telescope for the visual observer who wants aperture without electronics. Its simple, robust Dobsonian mount allows for intuitive "push-to" navigation of the night sky, making it an ideal workhorse for deep-sky observers.

The hybrid truss design addresses the primary challenge of large Dobsonians: portability. By allowing the optical tube to be disassembled, it makes dark-sky trips feasible without requiring a large vehicle. Disassembly does not require tools.

254mm of Aperture at f/5: The Light-Gathering Engine

The heart of this telescope is its 254mm (10-inch) parabolic primary mirror. This large aperture gathers hundreds of times more light than the naked eye, and bright star clusters are resolved to the core. The parabolic primary mirror is aluminum coated with a protective layer and 94% reflectivity.

The optical system's 1270mm focal length results in a fast f/5 focal ratio. With a 2-inch eyepiece the widest field at 1270mm is about 2 degrees, enough for the core of the Andromeda Galaxy (M31) or one arc of the Veil Nebula. The 68mm secondary mirror gives a central obstruction of 26.8% by diameter.

What You Can See with a 10-inch Telescope

With 254mm of aperture, you can explore a vast range of celestial targets. The included eyepieces provide magnifications of 51x (25mm) and 127x (10mm), offering flexibility for different objects.

• The Moon: Observe craters, mountains and maria, especially when less than half the Moon is lit and shadows along the terminator create a three-dimensional effect. The included Moon filter reduces the glare.
• Planets: On Jupiter you can see the cloud bands and the four Galilean moons, and sometimes a moon's shadow on the disc. The Cassini Division in Saturn's rings should be easily seen on nights of steady air, with Titan and up to six moons. Mars shows a small disc with a white polar patch, best near close approaches.
• Deep-Sky Objects: Bright star clusters are resolved to the core. The Great Orion Nebula (M42) shows structure, and under dark skies the core of the Andromeda Galaxy (M31) shows features. Galaxy fields such as those in Virgo and Coma become a hunting ground.

A Hybrid Truss Design for Portability and Stability

It is called a hybrid truss-tube Dobsonian because the secondary mirror is held inside a tube, like a traditional Dobsonian, rather than an open cage; the solid upper assembly protects the secondary mirror. It connects to the mirror box through four pairs of trusses, and the structure is optimized for maximum stiffness with minimal weight.

Disassembly does not require tools. Knobs lock the truss pairs to the mirror box, and small knobs secure the secondary mirror assembly to the trusses. The 15.8 kg optical tube breaks down into pieces that transport trouble-free, even in small cars.

Manual Motion with the Alignment Clutch System

The Dobsonian base, or rocker box, provides a simple and stable platform for the optical tube. The telescope pivots on large altitude wheels, allowing for smooth up-and-down motion. Two alignment clutches, one on each side of the rocker box, press a white tension pad against the altitude wheels.

Screwing in each large knob until the pad presses firmly against the wheel lets the telescope move up and down but not slip. The high altitude bearings and aluminum structures allow fine-adjustment flow at high magnifications. Because the base does not track, you nudge the telescope to follow objects as the Earth turns.

A 2-inch Focuser with 2 Plössl Eyepieces

The telescope is equipped with a 2-inch single-speed focuser, providing a wide light path for low-power, wide-field eyepieces. A 1.25-inch adapter is included to accommodate the two supplied Plössl eyepieces. A tension screw tightens a compression ring lock on the eyepiece, and loosening the three tension collar screws removes the 1.25-inch adapter for 2-inch eyepieces (sold separately).

To ensure eyepieces can reach focus, the telescope includes two extension tubes, a 25mm and a 20mm. The 25mm tube comes pre-installed, and the 20mm can be added as needed. The included eyepieces are:

• 25mm Plössl (1.25"): 51x, for locating objects and viewing star clusters and nebulae.
• 10mm Plössl (1.25"): 127x, for the Moon and planets.

Locating Objects with the Red-Dot Finder

Included with the telescope is a red-dot finder, powered by the supplied CR2032 battery. The finder projects a small, non-magnified red dot onto a glass window. When you look through the finder, you see the dot superimposed on the night sky.

Align it once it is dark, because the red dot is hard to see in daylight: center an object more than 800 yards away, such as a street lamp, in a low-power eyepiece, then adjust the finder's two screws until the red dot sits on the same object. Once aligned, you can simply move the telescope until the red dot is pointing at your desired star or planet, and it will be visible in the low-power eyepiece.

A 3-Step Process for Mirror Alignment

Collimation, aligning the telescope's mirrors, is needed for the sharpest images. It should take only a few minutes after reassembly if you have numbered your trusses.

1. Secondary Mirror Alignment: Look into the focuser. If the secondary mirror does not appear round, tilt it with the three collimation screws on the back of the secondary holder, then center the reflection of the small mark at the middle of the main mirror.
2. Primary Mirror Alignment: Look through the included collimation tool and adjust the primary mirror adjustment screws until the reflections of your eye and the secondary mirror are centered in the main mirror.
3. Fine Collimation (Star Test): Let the telescope adapt to the air temperature (up to 30 minutes), center Polaris at high magnification and adjust the primary mirror until the star image is concentric, recentering the star after each turn.

Transporting the 24.7 kg Telescope

The primary advantage of the hybrid truss design is its portability. The entire system has a total weight of 24.7 kg (54.35 lb), but it breaks down into lighter, more manageable components for transport.

• Optical Tube Assembly: The fully assembled OTA weighs 15.8 kg (35 lb). However, it disassembles into the mirror box (14.3 kg / 31.5 lb), the secondary cage (2.9 kg / 6.35 lb), and four truss pairs (0.45 kg / 1 lb each).
• Dobsonian Base: The altitude (rocker) box weighs 5.7 kg (12.5 lb).

Disassembly needs no tools and the scope transports trouble-free, even in small cars. Mark the altitude wheel and truss positions with luminous paint so reassembly at night goes right first time.

The Included Accessories

The included accessory set equips you to start observing immediately.

• 25mm and 10mm Plössl Eyepieces: A versatile pair for low-power searching and high-power viewing.
• Red-Dot Finder: For easy and intuitive aiming of the telescope.
• Collimation Tool: For aligning the main mirror.
• Moon Filter: Reduces the Moon's glare.
• Planisphere and Moon Map: For finding constellations and identifying lunar features.
• 25mm & 20mm Extension Tubes: Added as needed so the eyepiece can focus.

First Light Guide: Setup, Safety, and First Observations

Your first night with a new telescope is an exciting experience. Start during dusk to familiarize yourself with the assembly and alignment of the red-dot finder on a distant land object. Once it's dark, begin with an easy target like the Moon or a bright planet like Jupiter or Saturn. Use the 25mm eyepiece first to get a wide view, center the object, and focus carefully. Then you can switch to the 10mm eyepiece for a closer look.

SUN WARNING: Never attempt to observe the Sun with this device, and do not point the telescope or its finder at or near the Sun. Observing the Sun, even for a moment, will cause instant and irreversible damage to your eye or even blindness. Eye damage is often painless, so there is no warning until it is too late. Children should always have adult supervision while observing.