Halden Arcus 13 mm ultra-wide eyepiece

Specifications

Description

The Arcus 13 mm is a seven-element ultra-wide eyepiece with an 82-degree apparent field and a 1.25 in barrel. The wide field gives an immersive view, where the edge of the field sits at the edge of your vision and the sky seems to fill the eyepiece.

In a 1,200 mm Dobsonian, the Arcus 13 mm gives 92x and a true field of about 0.87 degrees. That is medium magnification with nearly the field of a 25 mm Plössl, so globular clusters and galaxies appear larger while still surrounded by sky. In a telescope without tracking, the wide field also gives more time before an object drifts out of view.

The design corrects astigmatism and field curvature well, keeping stars sharp to near the edge in telescopes as fast as f/5. In faster Newtonians, a coma corrector sharpens the outer field, since coma comes from the telescope rather than the eyepiece. The lenses are fully multi-coated with blackened edges.

The eye relief of 15 mm suits observers without glasses. Some glasses wearers can see most of the field, but the full 82 degrees requires your eye to be close to the lens. A winged eyeguard helps hold your eye in the right position.

The Arcus 13 mm has a 1.25 in barrel with a 2 in skirt, so it fits either focuser size. At 300 g, it is heavier than simple eyepieces; check the balance of light telescopes after you insert it.

The Arcus line is designed for observers who spend long sessions on deep-sky objects and want the field to feel open.

About this configuration

All configurations of the Halden Arcus 13 mm ultra-wide eyepiece share the same optical design; the options change the eyecup, the case, and the finish. This configuration comes without a case, which suits observers who keep their eyepieces in a shared foam box. No case is included, so the eyepiece ships in a simple box with its two dust caps fitted. A fold-down eyecup is simple and has no moving parts that can loosen in cold weather.

The black body with a color ring lets you tell focal lengths apart quickly under a red flashlight. This is the 2024 edition, which revised the undercut on the barrel and the grip rings of the Arcus line. The true field in your telescope is roughly the apparent field divided by the magnification you reach with this eyepiece.

What's in the box

• Eyepiece with fold-down rubber eyecup
• Top and bottom dust caps
• Foam-lined storage case

Compatibility notes

• Fits 1.25 in focusers directly and 2 in focusers through its 2 in skirt.
• The barrel accepts standard 1.25 in filters (M28.5 x 0.6 thread).
• Sharp to the edge at f/5 and slower; use a coma corrector in faster Newtonians.