Halden Ridgeline 100 Dobsonian, with Dobsonian base

Specifications

Description

The Ridgeline 100 Dobsonian is a 100 mm Newtonian reflector mounted on a simple alt-azimuth base. Its parabolic primary mirror has a focal length of 500 mm, giving a focal ratio of f/5. At that ratio, low-power eyepieces produce a wide field suited to star clouds and large open clusters, while a 6 mm eyepiece reaches about 83 times magnification for lunar craters and the rings of Saturn.

The tube is a one-piece rolled steel design with a matte black interior and a baffled light shroud at the front, which limits stray light from nearby streetlights. Three collimation screws on the mirror cell let you align the primary mirror with a laser collimator or a sight tube. Because the mirror is open to the air, it reaches outdoor temperature within about an hour, which helps keep images steady during the evening.

The Dobsonian base uses a Teflon-faced altitude bearing and a plywood azimuth platform, so the tube moves smoothly by hand without a motor drive. The 2 in dual-speed rack-and-pinion focuser accepts 2 in eyepieces directly and 1.25 in eyepieces through a supplied adapter. A 6x30 right-angle finder helps you locate targets at low power before you switch to a higher-magnification eyepiece. The tube weighs 6.5 kg, and the base packs separately, so you can carry the two sections to an observing site.

Typical targets include the Orion Nebula, the Double Cluster in Perseus, and M13 in Hercules, which resolves into individual stars at moderate power under dark skies. The 100 mm aperture gathers about four times the light of a 50 mm instrument, so fainter galaxies such as M81 and M82 show more structure than they do in smaller telescopes. Planetary detail is best during steady air, when Jupiter's bands and the Cassini Division in Saturn's rings are easiest to see.

About this configuration

The Halden Ridgeline 100 Dobsonian is offered in several configurations, and the notes below describe what this particular combination adds or changes. The Dobsonian rocker base keeps the telescope low and stable, and you aim it by pushing the tube gently by hand. A Dobsonian base needs no alignment, so you can set it on level ground and start observing within a few minutes. The matte black finish hides scuffs and keeps reflections from porch lights and streetlights to a minimum.

A UHC filter from the deep-sky kit darkens the background sky around emission nebulae, especially under suburban light. This is the 2025 edition, which updated the knobs and clamps so you can operate them with gloves on cold nights. Check the specifications table for the optical figures, since they stay the same across every configuration of the Ridgeline line.

What's in the box

• Optical tube assembly with primary mirror cell
• Dobsonian alt-azimuth base
• 2 in dual-speed rack-and-pinion focuser
• 2 in star diagonal with 1.25 in adapter
• 6x30 right-angle finder
• Front and rear dust caps
• Dobsonian rocker base with altitude bearings
• 24 mm wide-field eyepiece (1.25 in)
• UHC nebula filter (1.25 in)

Compatibility notes

• Accepts 2 in eyepieces directly and 1.25 in eyepieces through the supplied adapter.
• The base is designed for the tube alone and does not require a separate mount.
• The focuser has a T2 thread for camera adapters once you remove the 2 in nosepiece.