Explore Scientific 72° ED Series 8.5mm Waterproof Eyepiece (1.25")

A high-power eyepiece you can use on more nights

The Explore Scientific 72° ED Series 8.5mm Waterproof Eyepiece is a high-power eyepiece that's a little more forgiving than the 6.5mm when the air is unsteady. It has a 72° apparent field, a 1.25" barrel, 18mm of eye relief and a 10.5mm 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.

Key specs: 8.5mm focal length · 72° apparent field · 1.25" barrel · 18mm eye relief · 10.5mm field stop · 7 elements in 5 groups · H-FK61 ED glass · waterproof

What you'll see

• Planets on average nights: Jupiter's belts and moons, Saturn's rings and Mars when it's close.
• Globular clusters: M13 and M92 begin to resolve into individual stars in larger telescopes.
• Planetary nebulae and doubles: the Ring Nebula, the Cat's Eye Nebula and Albireo.

In an 8" Dobsonian (1200mm) the 8.5mm gives 141x and a 0.50° true field. In an 80mm f/6 refractor (480mm) it gives 56x and a 1.25° 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 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 4.25mm.
• More of the series: pair it with the 11.5mm and 6.5mm 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 8.5mm eyepiece with dust caps

Diagonals, Barlows and filters are sold separately.

Explore Scientific 72° ED 8.5mm 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 8.5. In an 8" f/6 Dobsonian (1200mm) that's 141x; in an 80mm f/6 refractor (480mm) it's 56x; in a Celestron 8" SCT (2032mm) it's 239x.

Can I use it with glasses?

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

8.5mm, 6.5mm or 11.5mm?

The 6.5mm gives more magnification (185x in an 8" Dob) for smaller, brighter targets. The 11.5mm gives a wider, brighter view (104x, 0.69°). The 8.5mm sits between them at 141x.

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