Explore Scientific 72° ED Series 25mm Waterproof Eyepiece (2")

Wide, low-power views for a 2-inch focuser

The Explore Scientific 72° ED Series 25mm Waterproof Eyepiece is a 2-inch low-power eyepiece for expansive views of big clusters and nebulae. It has a 72° apparent field, a 2" barrel, 18mm of eye relief and a 30.4mm 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 430g (15.2oz).

Key specs: 25mm focal length · 72° apparent field · 2" barrel · 18mm eye relief · 30.4mm field stop · 6 elements in 4 groups · H-FK61 ED glass · waterproof · 430g (15.2oz)

What you'll see

• The Double Cluster in Perseus, both clusters in one view.
• M81 and M82 together, and the Andromeda Galaxy with M32 and M110.
• Large nebulae: the Veil Nebula and North America Nebula in sections with a UHC or OIII filter.

In an 8" Dobsonian (1200mm) the 25mm gives 48x and a 1.45° true field. In an 80mm f/6 refractor (480mm) it gives 19x and a 3.63° 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.
• 18mm eye relief: comfortable for most eyeglass wearers.
• 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 nebula filter: a 2" UHC or OIII filter threads onto the barrel and makes the Veil and North America Nebulae stand out from suburban skies.
• A Barlow: the Tele Vue 2x Big Barlow doubles the magnification and turns this eyepiece into an effective 12.5mm.
• More of the series: pair it with the 30mm and 20mm 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 25mm eyepiece with dust caps

Diagonals, Barlows and filters are sold separately.

Explore Scientific 72° ED 25mm 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 25. In an 8" f/6 Dobsonian (1200mm) that's 48x; in an 80mm f/6 refractor (480mm) it's 19x; in a Celestron 8" SCT (2032mm) it's 81x.

Can I use it with glasses?

Yes. 18mm of eye relief is enough for most people who observe with glasses.

25mm, 20mm or 30mm?

The 20mm gives more magnification (60x in an 8" Dob) for smaller, brighter targets. The 30mm gives a wider, brighter view (40x, 1.78°). The 25mm sits between them at 48x.

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