Halden Tarn 100 Maksutov-Cassegrain, tube with alt-az mount

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

This listing covers one specific configuration of the Halden Tarn 100 Maksutov-Cassegrain, defined by its bundle, finish, accessory kit, and edition year. An alt-az mount keeps setup short: level the tripod, attach the tube, align the finder, and start finding targets. Manual alt-az motion suits visual observing, though you need to nudge the tube now and then to follow objects as the sky turns. The gloss white tube reflects sunlight, which helps it stay closer to air temperature while you set up before dusk.

Color filters from the planetary kit can bring out surface markings on Mars and the cloud belts of Jupiter. This is the 2024 edition, which revised the packaging and the accessory fittings of the Tarn line. 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
• Alt-az mount with aluminum tripod
• 6 mm planetary eyepiece (1.25 in)
• Four color filters (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.