Brightwell Orbit 5 mm planetary eyepiece, with hard case

Specifications

Description

The Orbit 5 mm is a six-element planetary eyepiece with a 58-degree apparent field and a 1.25 in barrel. It is designed to give high magnification with comfortable eye relief, which simple short focal length designs cannot do.

In a 1,200 mm Dobsonian, the Orbit 5 mm gives 240x. In a 700 mm refractor it gives 140x, and in a 1,500 mm Maksutov it gives 300x. Those magnifications suit the planets, the Moon, close double stars, and small planetary nebulae on nights when the air is steady.

The design places a negative lens group at the bottom of the barrel, which lengthens the eye relief to 16 mm. That lets you view with glasses and keeps your eye at a relaxed distance during long planetary sessions, when you wait for moments of steady air to reveal fine detail.

The lenses are fully multi-coated, and the internal surfaces are blackened to keep contrast high. A twist-up eyecup sets the eye position, and the 58-degree field gives a bit more time before an object drifts out of view in a telescope that does not track.

Magnification is limited by the atmosphere as much as by the telescope. On many nights, the air allows only 150x to 200x, so the Orbit 5 mm is a tool for the better nights. In a small telescope, it often runs close to the useful limit of the aperture, which is about twice the aperture in millimeters.

Pair the Orbit 5 mm with a medium-power eyepiece in the 10 mm to 15 mm range, so you can step down when seeing is poor.

About this configuration

All configurations of the Brightwell Orbit 5 mm planetary eyepiece share the same optical design; the options change the eyecup, the case, and the finish. The hard foam-lined case protects the eyepiece from knocks during travel and stacks neatly with other cases. A hard case keeps the eyepiece safe in a busy accessory box at a star party or an outreach event. A fold-down eyecup is simple and has no moving parts that can loosen in cold weather.

A color ring near the top of the body marks the focal length, which helps when you swap eyepieces in the dark. The optics in the 2024 edition match the other years; the changes concern the housing only. 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 twist-up eyecup
• Top and bottom dust caps
• Plastic storage case
• Hard foam-lined case

Compatibility notes

• Fits any 1.25 in focuser or diagonal.
• The barrel accepts standard 1.25 in filters (M28.5 x 0.6 thread).
• Gives 240x in a 1,200 mm telescope; check that this is within the useful limit of your aperture.