Explore Scientific 92° ED Series 20mm Waterproof Eyepiece (2")

Immersive deep-sky views with 20mm of eye relief

The Explore Scientific 92° ED Series 20mm Waterproof Eyepiece is a wide-field deep-sky eyepiece that balances brightness and magnification. It has a 92° apparent field, a 2" barrel, 20.2mm of eye relief and a 31.7mm field stop, and its 9 elements in 6 groups include H-FK61 ED glass to keep color fringing low and contrast high. Explore Scientific builds the series to be waterproof.

Key specs: 20mm focal length · 92° apparent field · 2" barrel · 20.2mm eye relief · 31.7mm field stop · 9 elements in 6 groups · H-FK61 ED glass · waterproof

What you'll see

• The whole Moon with sky around it in an 8" Dobsonian.
• The Double Cluster in Perseus and the Beehive Cluster, each filling a wide, sharp field.
• Big nebulae: the Lagoon and Trifid Nebulae together, and sections of the Veil Nebula with an OIII filter.

In an 8" Dobsonian (1200mm) the 20mm gives 60x and a 1.51° true field. In an 80mm f/6 refractor (480mm) it gives 24x and a 3.78° field. For comparison, the full Moon is about 0.5° across.

Why the 92° ED series

• A field you look into, not through: at 92° the edge of the view sits at the edge of your vision, so the eyepiece's field stop seems to disappear. On a Dobsonian or other undriven mount, objects also take longer to drift out of view.
• 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.
• 20.2mm eye relief: comfortable for most eyeglass wearers, which is rare in fields this wide.
• 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 2" diagonal or focuser (required): refractors and Schmidt-Cassegrains need a 2" diagonal such as the Explore Scientific 2" Diagonal or Celestron 2" Dielectric Star Diagonal. Most Dobsonians with a 2" focuser take it directly.
• A solid focuser: these are large eyepieces (164mm × 77mm), so a 2" focuser with a compression ring holds them best. Rebalance a Dobsonian or refractor after inserting one.
• A nebula filter: a 2" UHC or OIII filter threads onto the barrel for emission nebulae from suburban skies.
• A Barlow: the Tele Vue 2x Big Barlow doubles the magnification, turning this eyepiece into an effective 10mm.

Which 92° ED eyepiece is right for you?

Want something smaller and lighter? The 72° ED series uses the same ED glass in a narrower field. See all our eyepieces.

What's in the box

• Explore Scientific 92° ED 20mm eyepiece with dust caps

Diagonals, Barlows and filters are sold separately.

Explore Scientific 92° ED 20mm FAQ

Will it fit my telescope?

It has a 2" barrel, so it needs a 2" focuser or diagonal. It won't fit a 1.25"-only focuser.

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?

Yes. 20.2mm of eye relief is enough for most people who observe with glasses.

92° or 72°?

The 92° ED shows about 60% more sky at the same magnification and makes objects feel immersive, especially in a Dobsonian. The 72° ED series is smaller, lighter and less expensive, and easier to balance on small telescopes.

Is it really waterproof?

Explore Scientific sells the 92° ED series as waterproof eyepieces, which helps on dewy nights and when cleaning. Dry it before putting the caps back on.

Specifications