The straightforward way to build a 31mm wide-field eyepiece is to scale up what already works. TeleVue took one look at where that math led — a seven-lens design the size and weight of a bowling ball — and went back to the drawing board. What came out the other side is the Type 5: a six-element optical design with rare earth glass, 82 degrees of apparent field, and a weight of 35 ounces. That last number deserves a moment of your attention before you read any further.
Thirty-five ounces is not light. On a Dobsonian, switching from a short 1.25" eyepiece to this one may require rebalancing your scope. TeleVue makes a #TVEQC equalizing adapter specifically for this situation, and if you own a large Dob, it's worth having. That said: this eyepiece is heavier than you'd like, and it will likely become the eyepiece you reach for more than any other you own. These facts coexist comfortably once you've used it.
The engineering behind the Type 5 deserves a plain-English explanation. Some of the six optical elements are over 70mm in diameter — larger than the objective lens of TeleVue's own Pronto refractor. Four of the six elements use exotic glass formulations. The result is a 42mm field stop, the largest possible in a 2" barrel, delivering the widest true field you can achieve without going to a 3" focuser. TeleVue individually tests every eyepiece before it ships.
What's Included
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TeleVue 31mm Nagler Type 5 eyepiece (2" barrel)
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Fold-down eyeguard
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Rubber grip ring
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Eyeguard cover
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Undercut barrel
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2" filter thread compatibility
Features
82° Apparent Field of View — The Nagler standard — wide enough that experienced observers consistently describe it as looking through a porthole rather than a tube. Objects track across the field slowly enough that you notice the movement before they exit.
Six-Element Type 5 Design — The previous Nagler formula applied to a 31mm focal length would have produced something unacceptably large and heavy. The Type 5 design solves this with six elements and four exotic glass types, maintaining the contrast and edge sharpness the Nagler line is known for while keeping the package to a manageable size.
19mm Eye Relief — Comfortable for eyeglass wearers. Long enough that you're not pressing your eye against the glass, short enough that you're not hunting for the sweet spot. The fold-down eyeguard accommodates both.
Rare Earth Glass Elements — Multiple elements exceed 70mm in diameter — physically larger than some small refractor objectives. The glass choices are what make the Type 5 optically practical at this focal length.
Full Multi-Coatings, Blackened Lens Edges — TeleVue's proprietary coatings are tuned, not generic. Blackened lens edges reduce scatter. Together they contribute to the contrast that makes the 31mm Nagler the preferred choice for observers hunting faint nebulosity in large aperture scopes.
Filter Threads — The 31mm Nagler is threaded to accept 2" filters.
Anodized Aluminum Body — The barrel undercut provides a positive lock in any standard focuser. At 35 ounces, you want confidence that it's secure.
Under the Night Sky
In an 8" f/6 Dobsonian, the 31mm Nagler delivers a true field of about 1.4° — wide enough to frame the Pleiades with room to spare, or to sweep the Virgo Galaxy Cluster in a single field. In a 12" or larger Dob the exit pupil stays in the useful range and the field becomes genuinely immersive. The Veil Nebula, the North America Nebula, large open clusters — objects that fragment into pieces in a narrower eyepiece hold together here.
What Cloudy Nights Members Say
“The TMB92SS with the 31mm Nagler provides one of the most remarkable rich field views obtainable in portable telescopes available today. The views simply have to be seen to be believed — a celestial window through which to experience the Universe that is, quite frankly, breathtaking in extent.”
“Under dark skies, the 31mm gets far more eyepiece time — most of the time I am using the 35mm Pan is because the 31mm is in another scope. The 31mm Nagler takes it to the next level. It’s wider and even more perfect.”
“I have a 31 Nagler, and it’s an amazing eyepiece. I use it in my TeleVue 101, and it’s just a lovely combo for widefield views. I have no desire in trying out other wider eyepieces.”
Observing Tip
The 31mm Nagler shines brightest under dark skies where the large exit pupil works in your favor. In light-polluted suburban skies, the wide field can work against you on diffuse objects — the background sky brightens along with the target. For urban observers, an OIII or UHC filter makes a significant difference. The 2" filter threads are there for a reason.
FAQ
Is this eyepiece compatible with my focuser? — The 31mm Nagler uses a standard 2" barrel with an undercut for extra security. Any focuser with a compression ring or thumbscrew will hold it securely. The undercut prevents the eyepiece from being pushed up into the focuser — a thoughtful detail given the weight.
Will it balance on my Dobsonian? — Possibly not without adjustment, especially if you're switching from a light 1.25" eyepiece. TeleVue makes the #TVEQC equalizing adapter to address this. If you own a large Dob and plan to use this eyepiece regularly, the adapter is worth having.
What telescopes work best with this eyepiece? — The 31mm Nagler is most at home in telescopes with focal lengths between 1000mm and 2000mm — long enough to keep the exit pupil in a useful range. Large Dobsonians from 8" aperture and up are the classic pairing. It also performs beautifully in long-focal-length refractors and SCTs.
Is it worth it? — That depends on your observing habits. If you spend significant time under dark skies with a large aperture scope, and you value wide-field views of nebulae, clusters, and the Milky Way, the 31mm Nagler is the standard by which other wide-field eyepieces at this focal length are judged. If you're primarily a planetary observer, you'll get less value from it. We're happy to talk through whether it fits your situation — call us.
How does it compare to other wide-field 2" eyepieces? — The 31mm Nagler competes with a short list of eyepieces at similar price points. What distinguishes it is TeleVue's individual testing program and the proven field performance of the Type 5 design over many years. Alternatives exist. The 31mm Nagler remains the benchmark.
