Explore Scientific 72° ED Series 20mm Waterproof Eyepiece (1.25")

Wide, low-power views in a 1.25-inch eyepiece

The Explore Scientific 72° ED Series 20mm Waterproof Eyepiece is a low-to-mid power wide-field eyepiece for scanning the sky and taking in large objects whole. It has a 72° apparent field, a 1.25" barrel, 15mm of eye relief and a 24.8mm field stop, and its optics include H-FK61 ED glass to keep color fringing low and contrast high. Explore Scientific builds the series to be waterproof, and this eyepiece weighs 330g (11.6oz).

Key specs: 20mm focal length · 72° apparent field · 1.25" barrel · 15mm eye relief · 24.8mm field stop · 6 elements in 4 groups · H-FK61 ED glass · waterproof · 330g (11.6oz)

What you'll see

• The whole Moon with space around it in most telescopes.
• Large nebulae and galaxies: the Orion Nebula with its outer wings, the core of the Andromeda Galaxy with M32, and the Lagoon and Trifid Nebulae together in shorter telescopes.
• Star clusters: the Double Cluster, the Beehive Cluster and M35 with NGC 2158.

In an 8" Dobsonian (1200mm) the 20mm gives 60x and a 1.18° true field. In an 80mm f/6 refractor (480mm) it gives 24x and a 2.96° field. For comparison, the full Moon is about 0.5° across.

Why the 72° ED series

• Wide without the bulk: 72° is wide enough to frame objects with plenty of sky around them, while keeping the eyepiece smaller and lighter than 82° and 100° designs.
• ED glass: an H-FK61 fluorophosphate element (Abbe number 81.6) reduces color fringing on bright stars, the Moon and planets. Coatings are multi-layer.
• 15mm eye relief: comfortable without glasses, and usable with them by many observers.
• Waterproof: dew and damp nights are less of a worry, and the eyepiece is easier to keep clean.

What to add for the best results

• A good diagonal: for refractors and Schmidt-Cassegrains, the Celestron 1.25" Dielectric Star Diagonal has a twist-lock that holds the eyepiece securely.
• A Barlow: the Celestron 2x Omni Barlow doubles the magnification, turning this eyepiece into an effective 10mm.
• More of the series: pair it with the 25mm and 15mm for a matched set with the same 72° field and feel.

Which 72° ED eyepiece is right for you?

See all our eyepieces.

What's in the box

• Explore Scientific 72° ED 20mm eyepiece with dust caps

Diagonals, Barlows and filters are sold separately.

Explore Scientific 72° ED 20mm FAQ

Will it fit my telescope?

It has a 1.25" barrel, which fits nearly every telescope, including those with 2" focusers when you use the 1.25" adapter they come with.

What magnification will I get?

Divide your telescope's focal length by 20. In an 8" f/6 Dobsonian (1200mm) that's 60x; in an 80mm f/6 refractor (480mm) it's 24x; in a Celestron 8" SCT (2032mm) it's 102x.

Can I use it with glasses?

It has 15mm of eye relief, which works without glasses and for many glasses wearers. If you need more, the 15mm and 25mm models have 18mm, and the 30mm and 40mm have 25mm and 31mm.

20mm, 15mm or 25mm?

The 15mm gives more magnification (80x in an 8" Dob) for smaller, brighter targets. The 25mm gives a wider, brighter view (48x, 1.45°). The 20mm sits between them at 60x.

Is it really waterproof?

Explore Scientific sells the 72° ED series as waterproof eyepieces, which helps on dewy nights and when cleaning. Dry it before putting the caps back on.

Specifications