Thirteen millimeters is the sweet spot for a lot of telescopes. In a 10-inch f/5 Dobsonian, it gives you 96x — enough magnification to resolve the stars in globular clusters, split moderate double stars, and darken the sky background behind faint nebulae, while still holding nearly a full degree of true field. In an f/7 refractor like the AT102EDL, it delivers 55x with a 1.8° field — the Pleiades sit inside the view with room to breathe. The Astro-Tech 13mm 100° XWA puts that kind of range into a single eyepiece, with an apparent field wide enough that you stop noticing where the view ends.
The Optics
Nine elements in six groups, fully multi-coated with blackened lens edges. The optical design is corrected for telescopes as fast as f/4 — astigmatism, field curvature, and lateral color are controlled well enough that the field stays sharp into the outer zones. At f/5 and slower, the correction is excellent to the edge. On Cloudy Nights, the 13mm XWA (identical optics whether branded AT, APM, or Lunt) is one of the most discussed eyepieces in the line. CN members consistently describe the contrast as excellent, and multiple experienced observers — including those who own TeleVue Ethos eyepieces — report that the performance gap with premium alternatives is much narrower than the price gap. One CN member calls the 13mm his most-used eyepiece in the entire XWA set. One Yotpo reviewer put it directly: the 13mm XWA delivers about 95% of a TeleVue at a third of the price.
Dual 1.25"/2" Barrel
The eyepiece comes with a removable 2" collar. Remove it and you have a 1.25" barrel for smaller focusers and diagonals. Both barrels have a safety groove machined into the chrome to engage your focuser's thumbscrew — the eyepiece stays put even if the thumbscrew loosens during observing. At 19 ounces, it's a substantial eyepiece, and the safety groove matters.
Eye Relief and Eyeglass Use
Eye relief is 15mm — enough for comfortable viewing without eyeglasses. With glasses, you'll lose some of the outer field, but with a 100° apparent field, you're moving your eye around to explore the edges regardless. The soft rolldown eyecup shields against ambient light and folds flat for eyeglass wearers.
Waterproof
O-ring sealed and waterproof. The practical benefits for astronomy: no internal fogging when you bring a cold eyepiece indoors or observe at freezing temperatures, no dust or fine grit working its way into the optical assembly, and the internal coatings stay protected from humidity and fungus over the life of the eyepiece.
What's Included
- Astro-Tech 13mm 100° XWA 1.25"/2" eyepiece
- Removable 2" collar (installed)
- Lens caps (top and bottom)
Features
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100° apparent field of view — Nearly 50% more viewing area than an 82° eyepiece at the same focal length. Deep-sky objects sit in context with their surrounding star fields, not cropped at the edges.
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9 elements in 6 groups, fully multi-coated — Blackened lens edges reduce internal scatter. Designed for high contrast and edge sharpness at focal ratios down to f/4.
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13mm focal length — A versatile mid-power focal length. 77x in a 1000mm scope, 96x in a 1250mm Dob, 55x in a 714mm refractor. Useful on everything from nebulae and clusters to planets and the Moon.
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15mm eye relief — Comfortable for extended sessions. Usable with eyeglasses, though some outer-field vignetting may occur.
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Dual 1.25"/2" barrel — Removable 2" collar lets you use the eyepiece in any focuser or diagonal. Safety groove on both barrels engages the focuser thumbscrew.
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Waterproof, O-ring sealed — Prevents internal fogging, resists dust intrusion, protects coatings from humidity and fungus.
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Soft rolldown eyecup — Blocks ambient light. Rolls flat for eyeglass wearers.
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19 ounces — Heavier than a standard eyepiece. Check your balance on lightweight scopes.
Under the Night Sky
In a 10-inch f/5 Dobsonian, the 13mm XWA gives you 96x and just under a degree of true field. That's the magnification range where globular clusters come alive — M13 starts resolving individual stars across its face, not just at the edges. M22 in Sagittarius shows its slightly elongated shape and begins breaking into chains and knots of stars. Omega Centauri, if you can reach it, is a city of stars filling a good portion of the field.
Point it at the Orion Nebula and the nebulosity pops against a darker sky background than you'd get at lower power. The Trapezium is cleanly split, and the wings of M42 extend well out from center. Move to M1, the Crab Nebula, and the oval glow shows its slightly mottled texture — something that washes out at lower magnification.
On planets, 96x is a good starting point for Jupiter — the two main equatorial belts are obvious, the Great Red Spot is visible when it transits, and the Galilean moons show as tiny disks rather than points. Saturn's rings are cleanly separated from the globe with Cassini's Division visible on steady nights. This isn't a high-power planetary eyepiece, but the 100° field gives you a long drift time on an untracked Dob before the planet exits the view.
In a shorter refractor like the AT86EDQ at 500mm, the 13mm runs 38x with a 2.6° field — open clusters like M35, M37, and the Double Cluster are framed beautifully, fully resolved against a dark background with plenty of surrounding star field for context.
Observing Tip
The 13mm XWA pairs exceptionally well with a UHC or O-III nebula filter on Dobsonians. At 96x in a 10-inch, you're at the sweet spot where the filter darkens the background enough to pull faint nebulosity out of the glow, while the magnification is high enough to show structural detail. Try it on the Veil Nebula — Pickering's Triangle and the thin filaments along NGC 6992 become visible in a way that lower-power views can't match.
FAQ
How does this compare to the Astro-Tech 13mm 82° UWA?
The 82° UWA is lighter (about 10 oz), less expensive, and has an 82° field. The 100° XWA has a wider field, more glass (9 elements vs. fewer), and is waterproof. If the wider field and sealed construction matter to you, the XWA is the upgrade. If weight and cost are the priority, the 82° UWA is excellent in its own right.
Is this eyepiece parfocal with other XWAs in the line?
The XWA eyepieces are close to parfocal with each other, though you may need a small focus adjustment when swapping between focal lengths. They're not guaranteed parfocal with eyepieces from other lines.
Can I use this with a Barlow?
Yes. A 2x Barlow effectively turns the 13mm into a 6.5mm with 100° apparent field — very high power with a wide view. Use the 1.25" barrel (collar removed) in a 1.25" Barlow, or the 2" barrel in a 2" Barlow. Be aware that a Barlow adds optical elements and may slightly affect edge performance.
Will 19 ounces cause balance problems?
On medium and large Dobsonians, no — the scope has enough mass to absorb the weight. On lightweight refractors, small tabletop Dobs, or alt-az mounts near their capacity, the eyepiece may tip the balance. Check before letting go of the tube.
Final Thoughts
The 13mm XWA occupies the middle of the magnification range in most telescopes — high enough for detail, low enough for context. It resolves globular clusters, shows planetary detail, and frames nebulae against dark backgrounds, all while holding a 100° field that makes tracking on a Dobsonian feel optional. At 19 ounces it's not a featherweight, and at 9 elements it's not optically simple. But it delivers a view that makes you forget about the hardware and focus on the sky, and that's the entire point of an eyepiece. Owners who've compared it to eyepieces at three times the price have come away impressed — and that tells you more than any spec sheet can.
