Corvane Basalt 102 Dobsonian, tube only

Specifications

Description

The Basalt 102 Dobsonian is a Newtonian reflector mounted on a rocker-box base. Its primary mirror has an aperture of 102 mm and a focal length of 510 mm, which gives a focal ratio of f/5. At this ratio the tube is short enough to sit at a comfortable height on a low table, and the field is wide enough to frame large extended objects at low power. The rocker base turns in azimuth and tilts in altitude, so you can move the tube by hand to follow an object across the sky. Set the instrument on a flat, firm surface and it needs no tripod, which makes it practical for observing from a backyard or a park.

The primary mirror is coated with aluminum and protected by a dust cover, and the secondary mirror is held by a four-vane spider. The spider adds faint diffraction spikes around bright stars, a feature that is typical of this design. The 1.25 in rack-and-pinion focuser accepts standard eyepieces and holds them firmly at the focal plane. Because of the f/5 ratio, a 25 mm eyepiece gives a wide field for star clusters, and a 6 mm eyepiece takes you to higher power for lunar and planetary work. Collimation, the alignment of the two mirrors, is adjusted with three screws at the back of the mirror cell. Check it at the start of each session, since a well-collimated mirror gives sharper images of Jupiter and Saturn.

The tube weighs 6.9 kg and the rocker base carries it without strain on a level surface. Typical targets include the Orion Nebula, the Ring Nebula in Lyra, and the globular cluster M13 in Hercules, which show more detail under dark skies. Plan your session around the Moon, since moonlight reduces contrast in faint nebulae and galaxies. Let the tube reach outdoor temperature before observing, which takes about thirty minutes for a closed-tube reflector of this size.

About this configuration

The Corvane Basalt 102 Dobsonian is offered in several configurations, and the notes below describe what this particular combination adds or changes. This is the optical tube on its own, so you need to supply a mount that can carry its weight steadily. Buying the tube alone makes sense if you already own a suitable mount or plan to choose one separately. The carbon fiber tube expands less as the temperature drops, so the focus point drifts less as the night cools.

The deep-sky kit adds a wide-field eyepiece and a UHC filter for emission nebulae such as the Lagoon and the Orion Nebula. The 2023 edition uses the same optical design as later years, with small differences in fittings and labels. The optical figures in the specifications table apply to this configuration and to every other version of the Corvane Basalt 102 Dobsonian.

What's in the box

• Optical tube assembly
• Rocker-box base with altitude and azimuth bearings
• Pre-aligned primary and secondary mirrors
• 1.25 in rack-and-pinion focuser
• Red-dot finder
• Dust cover
• 24 mm wide-field eyepiece (1.25 in)
• UHC nebula filter (1.25 in)

Compatibility notes

• Accepts 1.25 in eyepieces directly in the focuser.
• The rocker base works best on a firm, level surface such as a patio or a sturdy table.