Halden Tarn 100 Maksutov-Cassegrain, tube only

Specifications

Description

The Tarn 100 Maksutov-Cassegrain is a catadioptric telescope built around a thick meniscus corrector plate, a spherical primary mirror, and a secondary mirror formed as an aluminized spot on the back of the corrector. With 100 mm of aperture and 1200 mm of focal length, it works at f/12. That ratio gives a narrow field and high magnification, which suits lunar detail, planetary disks, and close double stars.

Because the secondary is part of the corrector, the light path has no spider vanes, and the sealed tube keeps dust off the optics. Light reflects off the primary, returns to the spot on the corrector, and passes back through a hole in the primary to the focuser at the rear of the tube. Both the corrector and the mirror are coated to limit light loss. The thick glass element and closed tube hold heat, so allow about an hour for the tube to reach outdoor temperature before you use high power on the Moon or planets.

The tube weighs 4.2 kg, so it suits a light alt-az mount or a small equatorial mount. The 2 in rack-and-pinion focuser accepts a 1.25 in adapter for lighter eyepieces, and the fine-focus knob gives smooth control at high magnification. An 8x30 right-angle finder helps you locate targets before you move to the eyepiece. Typical targets include lunar craters along the terminator, Jupiter's belts, the rings of Saturn, the phases of Venus, and close doubles such as Epsilon Lyrae and Sigma Orionis. Wide-field eyepieces show less of large clusters than they would through a refractor, so this tube suits detail more than sweeping the sky.

About this configuration

The Halden Tarn 100 Maksutov-Cassegrain 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. A matte white finish reduces glare from nearby lights while keeping the tube easy to see at night.

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 Halden Tarn 100 Maksutov-Cassegrain.

What's in the box

• Optical tube with dust cap
• Vixen-style dovetail bar
• 2 in star diagonal with 1.25 in adapter
• 8x30 right-angle finder
• Front and rear dust caps
• 24 mm wide-field eyepiece (1.25 in)
• UHC nebula filter (1.25 in)

Compatibility notes

• Accepts 1.25 in eyepieces through the supplied adapter.
• The Vixen-style dovetail bar fits most small and medium mounts.
• The focuser has a T2 thread for camera adapters once you remove the 2 in nosepiece.