Brightwell Summit 4 mm Plössl eyepiece, with hard case

Specifications

Description

The Summit 4 mm Plössl is a four-element eyepiece with a 50-degree apparent field and a 1.25 in barrel. It is a high-power eyepiece. In a 500 mm refractor it gives 125x, in a 1,200 mm Dobsonian it gives 300x, and in a 2,032 mm Schmidt-Cassegrain it gives 508x. At these powers, small changes in focus, collimation, and tracking show quickly, so you will use it mostly on the Moon, bright planets, and close double stars.

The 3.2 mm field stop sets a narrow true field. In a 1,200 mm telescope it spans about 0.15 degrees, or roughly 9 arcminutes, which is enough to frame a planetary disk with some space around it. Because the apparent field is 50 degrees, the true field narrows quickly as focal length increases, so the eyepiece suits detailed views of small targets rather than wide sweeps of the sky. Start with a lower-power eyepiece to locate the object, then move up to this one once it is centred.

The Plössl design uses two cemented doublets facing each other. In telescopes slower than about f/6, it gives sharp stars across most of the field, with some softening at the edge in faster Newtonians. The lenses are fully multi-coated, and the barrel interior is blackened to reduce internal reflections that would lower contrast on the Moon and planets.

With 9 mm of eye relief, the eyepiece needs your eye close to the lens, so you will find the full field easiest to see with glasses off or with a short eyecup in place. The barrel is threaded for standard 1.25 in filters and fits any 1.25 in focuser or diagonal. The eyepiece weighs 45 g, which keeps it balanced on lightweight focusers in smaller telescopes.

About this configuration

The Brightwell Summit 4 mm Plössl eyepiece is offered in several configurations, and the notes below describe what this particular one adds. 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 winged eyeguard helps you hold your eye at the right position, which makes the edge of the field easier to see.

The black body with a color ring lets you tell focal lengths apart quickly under a red flashlight. This is the 2023 edition of the Summit line, the earliest version that is still listed in the catalog. 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
• Top and bottom dust caps
• Plastic storage case
• Hard foam-lined case
• Winged rubber eyeguard

Compatibility notes

• Fits any 1.25 in focuser, diagonal, or Barlow lens.
• The barrel accepts standard 1.25 in filters (M28.5 x 0.6 thread).
• Sharp across most of the field at f/6 and slower; softer at the edge in faster Newtonians.