High-power planetary eyepieces have a reputation problem: the higher the magnification, the narrower the view, and the faster the planet drifts out of the field. With a standard 50-degree eyepiece at 300×, Jupiter crosses your field of view in seconds. You spend more time nudging the scope than actually observing. The Astro-Tech 3.5mm XWA solves this the direct way — it delivers 110 degrees of apparent field, nearly 50% more viewing area than an 82-degree eyepiece at the same magnification. The planet still moves at the same rate, but you have a much wider window to watch it in. On a Dobsonian without tracking, that's the difference between glimpses and sustained observation.
The View at 110°
One hundred and ten degrees of apparent field is not like looking through a tube. It's closer to looking through a window. The field edge is in your peripheral vision — you're aware of it, but you're not bumping into it. At 3.5mm in an f/5 Dobsonian (1,250mm focal length), you're observing at 357× with a true field of roughly 0.31 degrees. In a conventional 50° Plössl at that magnification, the same true field would require constant tracking adjustments. With 110°, Jupiter or Saturn stays centered long enough to study belt detail, follow a moon transit, or wait for a moment of steady seeing.
The optical design uses 8 elements with full broadband multi-coatings on all air-to-glass surfaces and blackened lens edges to control stray light. The result is good contrast and well-controlled astigmatism, field curvature, and lateral color across the field — important in a design this wide, where off-axis aberrations can compromise the outer third of a lesser eyepiece. This eyepiece is designed to perform in fast telescopes down to f/4, so it handles the steep light cone of short-tube Newtonians and fast refractors without falling apart at the edges.
Built for the Field
The entire eyepiece is O-ring sealed against moisture. That matters for astronomy more than it might sound. Sealed construction prevents internal fogging during cold-weather sessions when temperatures drop rapidly. It keeps dust and fine particulates out of the optics in windy conditions. It blocks fungal growth in humid climates. And it means you can clean the exterior without worrying about solution seeping between elements. Five practical benefits from one engineering decision.
The barrel is dual-diameter — a 1.25" barrel with a removable 2" collar, so it fits either focuser size without an adapter. A safety groove machined into the barrel engages your focuser thumbscrew, preventing the eyepiece from falling out if the thumbscrew loosens during use. At 19 ounces, this eyepiece has real weight to it. That's the tradeoff for 8 elements and 110 degrees of field. On a solid mount it's a non-issue, but on a lightweight tabletop Dob or small refractor, you may need to rebalance.
The soft rolldown eyecup shields your eye from ambient light — helpful when a neighbor's security light or a fellow observer's headlamp wants to wreck your dark adaptation. Fold it down for eyeglass use.
What's Included
- Astro-Tech 3.5mm 110° waterproof XWA eyepiece
- Removable 2" barrel collar (1.25" barrel underneath)
- Dust caps
Features
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110° apparent field of view — The widest AFOV in the Astro-Tech lineup. Nearly 50% more viewing area than an 82° eyepiece, and more than four times the area of a 50° Plössl. Planets stay in view dramatically longer on untracked mounts.
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3.5mm focal length for serious high power — Delivers 257× in an f/6, 343× in an f/8, 357× in an f/5, and 571× in an f/10 SCT. This is the eyepiece for nights when the seeing is rock-steady and you want to push the magnification.
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8-element fully multi-coated optics — Full broadband multi-coatings on all air-to-glass surfaces keep internal reflections low and contrast high despite the complex multi-element design. Blackened lens edges further suppress scattered light.
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O-ring sealed / waterproof — Prevents internal fogging in cold, keeps out dust and moisture, blocks fungal growth in humid climates, and makes cleaning the exterior safe and simple.
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15mm eye relief — Comfortable for extended observing sessions, including use with eyeglasses. Soft rolldown eyecup adjusts for glasses-on or glasses-off viewing.
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Dual 1.25"/2" barrel — Removable 2" collar reveals a 1.25" barrel underneath. Fits any focuser without adapters. Safety groove engages the thumbscrew so the eyepiece can't fall out.
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Designed for fast telescopes (f/4 and above) — Well-controlled astigmatism and field curvature at fast focal ratios. Works with short-tube Newtonians, fast refractors, and Dobsonians without edge-of-field breakdown.
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6.7mm field stop — Determines the true field of view in your telescope. Divide 6.7mm by your telescope's focal length (in mm) and multiply by 57.3 to get your true field in degrees.
Observing Tip
The first time you look through a 110° eyepiece, your instinct will be to press your eye tight against the lens to see the whole field. Don't. Hold your eye at the full 15mm of relief, relax, and let the field fill your vision naturally. It takes a session or two to learn the viewing technique — the field edge is in your peripheral vision, not centered. Once you stop trying to "find" the edge and let the view come to you, the spaceship-window effect clicks, and you won't want to go back to a narrow field.
FAQ
Q: Is 3.5mm too much magnification for my scope?
It depends on your focal length and your sky conditions. A useful rule: divide your aperture in millimeters by 0.5 to get the theoretical maximum useful magnification. So a 200mm scope can handle up to 400×. But the atmosphere usually limits you to 200–300× on most nights. The 3.5mm XWA is built for the nights when the seeing cooperates and you want to push the limits. On average nights, it may be more magnification than the atmosphere supports — that's normal. Pair it with a longer XWA for nights when the seeing is less steady.
Q: How does 110° compare to an 82° eyepiece at the same focal length?
At the same focal length, you get the same magnification. The difference is field width. A 110° eyepiece shows nearly 50% more sky area than an 82° eyepiece. In practical terms, a planet drifts through the 110° field roughly a third longer before exiting. That extra time is the whole point — more observing, less nudging.
Q: Will it work with eyeglasses?
Yes. The 15mm eye relief accommodates most eyeglasses. Fold down the soft rolldown eyecup to bring your eye closer to the lens. You won't see the full 110° with glasses on — expect to lose some edge — but the usable field is still wider than most conventional eyepieces deliver at any focal length.
Q: The eyepiece weighs 19 ounces — will it tip my scope?
It might, on a lightweight setup. If you're using a small tabletop Dobsonian or a light refractor on a photo tripod, test the balance before loosening your altitude lock. On a solid equatorial mount or a full-size Dobsonian, 19 ounces won't be an issue. If you're concerned, have a counterweight ready or check the balance before pointing to zenith.
Q: Do I need the 2" barrel, or can I use it in a 1.25" focuser?
Both. The 2" collar is removable — unscrew it and you have a standard 1.25" barrel underneath with a safety groove. If your scope has a 2" focuser, use the full collar for a secure fit. If it only accepts 1.25", remove the collar. No adapter needed either way.
Final Thoughts
The 3.5mm XWA is not for every night or every scope. It's a specialized tool — the eyepiece you reach for when the atmosphere settles down and you want to push serious magnification without losing the target every few seconds. On a good night, with a scope that can feed it enough light and resolution, 110 degrees at high power is unlike anything a conventional eyepiece can deliver. The planet just sits there, suspended in a wide dark field, while you watch the details unfold. Sealed, dual-barrel, built for fast scopes. For the observer who already knows what magnification they need and wants the widest possible view when they get there.
