Halden Cascade 20 mm wide-field eyepiece, with hard case

Specifications

Description

The Cascade 20 mm is a seven-element wide-field eyepiece with a 70-degree apparent field and a 2 in barrel. Its 23.5 mm field stop sets a wide true field, and its 16 mm of eye relief lets most observers, including many who wear glasses, see the full field without pressing the eye against the lens. The eyepiece is intended for telescopes with a 2 in focuser or a 2 in diagonal.

A 20 mm eyepiece gives moderate magnification in most telescopes: 50x in a 1,000 mm f/5 refractor, 30x in a 600 mm reflector, and 100x in a 2,000 mm telescope. In the 1,000 mm telescope, the 23.5 mm field stop gives a true field of about 1.35 degrees, enough to frame open clusters and the bright core of a large nebula with the surrounding stars in view. The wide apparent field also keeps the stars near the edge of the view, which helps you keep your bearings while you move across the sky to a target.

The optical design has seven elements with fully multi-coated surfaces to reduce reflections and light loss. Image sharpness is strongest near the center of the field. In telescopes faster than about f/5, expect slight softening and field curvature toward the edge, because the light cone reaching the eyepiece is steeper. In slower instruments, from about f/8 to f/10, the stars remain sharp across most of the field.

The eyecup folds down for use with glasses and folds up to block stray light from the eye side of the barrel. The 2 in barrel weighs 520 g, a moderate load for a 2 in focuser. The barrel accepts standard 2 in filters for use with light pollution or moon filters.

About this configuration

All configurations of the Halden Cascade 20 mm wide-field 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. The fold-down rubber eyecup blocks stray light, and you can fold it back if you observe with glasses.

Titanium gray shows dust and fingerprints less than black, and it keeps a uniform look over time. The 2026 edition carries the optics over unchanged and updates small parts such as the caps and the markings. To find the magnification, divide the focal length of your telescope by the eyepiece focal length in the specifications.

What's in the box

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

Compatibility notes

• Fits any 2 in focuser or diagonal.
• Accepts standard 2 in filters.
• Sharp across most of the field at f/8 and slower; softer at the edge in faster telescopes.