Xtreme Wide Angle Eyepieces (XWA) 100°-120°
There is a moment that every astronomer experiences when they first look through an extreme wide-angle eyepiece. Instead of the usual circle of light surrounded by darkness, a view opens up that resembles a portal on a spacecraft - stars and nebulae spread in every direction, with no visible edge, as if you are truly floating through space. This is exactly the experience offered by XWA series ultra-wide-angle eyepieces with an apparent field of view of 100° to 120°. They represent the most extreme eyepieces available to amateur astronomers, and for many experienced observers they completely transform the way they look at the night sky.
What Does a 100° to 120° Field of View Actually Mean?
The standard eyepieces that most astronomers start with typically offer an apparent field of view between 50° and 60°. Wide Angle and Ultra Wide Angle eyepieces push this boundary to 68° to 82°. XWA eyepieces with 100° to 120° are in a category of their own - their apparent field of view is so large that the eye is physically unable to take in the entire image at once. The result is a complete sense of immersion in the object being observed.
Why does this field of view matter so much in practice? The true field of view of a telescope depends on the combination of the eyepiece focal length and the apparent field of view. An XWA 13 mm eyepiece with a 100° apparent field, for example, delivers more than twice the true field of view in the same telescope compared to a classic Plössl of the same focal length. This means that large objects such as the Andromeda Galaxy, the Pleiades, or vast emission nebulae fit entirely within the frame - while still maintaining useful magnification.
Optical Design - What Is Inside an XWA Eyepiece
Achieving genuinely high image quality across a field of view exceeding 100° is an extraordinarily demanding optical challenge. A standard five- or six-element design would fail at such an extreme viewing angle - the image would be blurred, distorted, and plagued by chromatic aberrations at the edges. XWA eyepieces therefore contain between eight and fourteen optical elements arranged in complex groups, with lenses made from specialist glass types with different refractive indices and dispersion characteristics.
The key technologies that make an extreme field of view possible while maintaining image quality include:
- Multi-layer anti-reflection coatings on all optical surfaces - minimising light loss and suppressing stray reflections that would otherwise drastically reduce contrast across so many optical interfaces
- ED glass (extra-low dispersion) combined with standard optical glass - controlling chromatic aberration, which becomes particularly pronounced at extreme field angles
- Precisely engineered aspherical surfaces - correcting spherical aberration and maintaining sharpness right to the edge of the field of view
- Fully sealed and nitrogen-purged construction in premium models - protecting the optics from moisture and preventing fogging during temperature changes
The result is an eyepiece that, despite its extreme angle of view, delivers surprisingly sharp and contrasty images. The best XWA models maintain acceptable sharpness across 95-100% of the field diameter - stars at the edge remain pinpoint or near-pinpoint, with no significant blur or coma.
Which Telescopes Are XWA Eyepieces Best Suited For?
Extreme wide-angle eyepieces can be used with virtually any type of telescope, but they truly shine in certain combinations. As a general rule, the faster the focal ratio of the telescope (lower f/ number), the more demanding it is to maintain sharpness across the entire field. An f/4 or f/5 telescope presents a significantly greater optical challenge for an XWA eyepiece than an f/8 or f/10 refractor. That said, premium XWA designs cope well even with fast Newtonians - manufacturers take this combination into account during development and optimise aberration correction for shorter focal ratios.
The most natural combination for XWA eyepieces is a large-aperture Dobsonian or Newtonian with apertures of 200 mm and above. It is precisely in these telescopes that the extreme field of view fully reveals itself - in a 12" or 16" Dobsonian with an XWA 17 mm eyepiece, sprawling emission nebulae, stellar associations, and groups of galaxies appear as a spectacular panorama that simply cannot be appreciated in the same way through a narrower field. At the same time, the aperture of the telescope ensures that even fainter objects are visible with good contrast during sweeping observation sessions.
XWA eyepieces are also an excellent choice for equatorially mounted refractors and catadioptric systems, where they work particularly well for wide-field surveys of star clusters, star-hopping navigation to fainter targets, or sweeping extended regions of the Milky Way.
How to Choose the Right XWA Focal Length
The choice of a specific XWA focal length depends on what you want to observe and on the specifications of your telescope. XWA eyepieces are available in focal lengths from approximately 3 mm to 25 mm, with each range having its own optimal application:
- 3-5 mm - high magnification for planetary and lunar observation, with a feeling of being immersed in the surface detail of the Moon or Jupiter's cloud belts
- 7-9 mm - medium magnification for globular clusters, planetary nebulae, and more detailed views of galaxies
- 13-17 mm - the most popular range for wide-field deep-sky observation, large emission nebulae, and open star clusters
- 20-25 mm - the widest true field of view, ideal for sweeping constellations, meteor watching, or simply enjoying sweeping views of the winter and summer Milky Way
When making your choice, we recommend calculating the true field of view for your specific telescope and eyepiece combination. Simply divide the apparent field of view of the eyepiece (100° or 110°) by the resulting magnification - this gives you the actual angular field in degrees and helps you estimate how large a section of sky will be visible.
Practical Aspects of Observing With XWA Eyepieces
Extreme wide-angle eyepieces tend to be larger in diameter and heavier than standard eyepieces. Before purchasing, it is worth checking whether the focuser on your telescope can hold the additional weight without slipping. Premium 2" XWA models can weigh between 400 and 700 grams - a lower-quality rack-and-pinion focuser may shift focus or allow the image to wobble under this load. With high-performance XWA eyepieces, a solid focuser is almost as important as the eyepiece itself.
The exit pupil of an XWA eyepiece can be relatively large at longer focal lengths. Under a dark sky this is an advantage, but when observing from light-polluted locations, a bright sky background can reduce contrast on faint objects. In such cases, an eyepiece with a shorter focal length and smaller exit pupil is the more practical choice.
Eye relief - the distance from the eye to the last optical element of the eyepiece - varies between XWA models. For comfortable observation, especially for eyeglass wearers, it is important to choose a model with at least 15-20 mm of eye relief. Many XWA eyepieces are very comfortable in this regard, but we always recommend checking this specification before purchasing.
XWA Eyepieces as an Investment in Your Astronomical Experience
XWA series eyepieces are among the most expensive eyepieces in amateur astronomy - and for good reason. Their optical complexity, the cost of premium glass, and precision mechanical construction are inevitably reflected in the price. Yet for many experienced astronomers they represent the single most rewarding purchase they have ever made for their telescope.
One quality XWA eyepiece can completely transform the way you experience your telescope. A globular cluster that appears as a compact ball of stars in a conventional eyepiece opens up in an XWA into a breathtaking three-dimensional swarm of stars filling the entire field. Vast nebulae such as the Orion Nebula or the Rosette, which rarely fit entirely into a standard eyepiece, suddenly appear in their full glory. And sweeping the Milky Way through an XWA eyepiece is an experience that simply cannot be described in words - it has to be seen.
If you are seriously considering purchasing an XWA eyepiece and are unsure which model and focal length will suit your telescope best, we are happy to help. Simply let us know the type and specifications of your telescope and, most importantly, what you most enjoy observing - and we will recommend a specific model that will bring you maximum pleasure every time you head out under the stars.
