Quillon Marlin 21 mm Plössl eyepiece, with hard case

Specifications

Description

The Marlin 21 mm is a four-element Plössl eyepiece with a 52-degree apparent field and a 1.25 in barrel. It sits in the middle of the focal range, between the low-power eyepieces that frame wide objects and the higher-power eyepieces that split close doubles and show planetary detail. Its 18 mm field stop sets the true field in each telescope, so the width of the view changes with focal length. It suits an observer building a set of three or four eyepieces.

A 21 mm eyepiece gives 33x in a 700 mm refractor, 57x in a 1,200 mm Dobsonian, and 97x in a 2,032 mm Schmidt-Cassegrain. In the 1,200 mm telescope, the true field is about 0.9 degrees, enough to frame a small open cluster or a compact group of galaxies. Moderate power gives a bright image with enough magnification to separate stars in open clusters and to show structure in brighter nebulae.

The Plössl design uses two cemented doublets facing each other. It gives sharp stars across most of the field in telescopes slower than about f/6, with some softening at the edge in faster Newtonians. The lenses are fully multi-coated, and the edges are blackened to reduce internal reflections that lower contrast under dark skies.

With 16 mm of eye relief, the Marlin 21 mm suits most observers, including many who wear glasses when the eyecup is folded down. At 80 g, it balances well on a diagonal and works in a binocular viewer. Pair it with a 10 mm eyepiece for higher power and a 32 mm eyepiece for wider fields.

About this configuration

The Quillon Marlin 21 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. The fold-down rubber eyecup blocks stray light, and you can fold it back if you observe with glasses.

A color ring near the top of the body marks the focal length, which helps when you swap eyepieces in the dark. The 2025 edition keeps the same optical figures as the earlier years of the Marlin 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
• Plastic storage case
• Hard foam-lined case

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.