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Astro-Tech’s 20mm XWA: An Affordable Extreme-Field Eyepiece

The Astro-Tech XWA comes in a plain vanilla box, with rubber end caps each the same size so they can be interchanged. Credit: Alan Dyer

A 20mm eyepiece with a 100° field for only $300 seems too good to be true!

In eyepieces, models with the extreme apparent field of 100° rank at the top for performance – but also price! Some models sell for as much as $700 to $1,000 each. When I saw that Astronomics, under their Astro-Tech house brand, was now offering a series of 100° eyepieces for $300 or less each, I was curious enough to buy one. 

I selected the 20mm XWA (for eXtreme Wide-Angle) which, at the time I purchased it, was on sale for $50 off the regular price of $299.95, making it even more of a bargain. It is the longest focal length in the series of six XWAs, which extends to a 4.7mm 110° model.

The 20mm XWA is 6.25 inches (15.8 cm) tall and weighs 1.52 pounds (691 grams), lighter than all competing 20mm 100° eyepieces, often by a wide margin, minimizing balance issues. Credit: Alan Dyer

XWA OPTICS

Having used top-of-the-line 100° eyepieces from Explore Scientific, Stellarvue (their Optimus series) and Tele Vue (their Ethos series), I knew what to expect from such an extreme-field eyepiece. I was fully expecting the XWA to provide performance commensurate with its low price, with stars not really sharp over the entire field but instead begin to fuzz out perhaps halfway toward the edge, making the wide field less than impressive.

I was pleasantly surprised to discover otherwise. Sharpness across the field came very close to matching the best. I did not have a Tele Vue 21mm Ethos to compare the XWA to, but I did do A-B tests against a 17mm Ethos. I used them on a 94mm f/5.5 Sharpstar apo refractor, a 105mm f/6 Astro-Physics apo refractor, and a Sky-Watcher 8-inch f/6 Newtonian reflector telescope.

In the Newtonian, stars in the XWA remained pinpoint across the central 75 percent of the field, softening only slightly in the outer 25 percent, though without growing noticeable “wings” from astigmatism or coma. This was only slightly worse than the much more costly Ethos, where stars also softened in the outer 25 percent, but remained a little tighter at the edge.

In the refractors, the XWA also performed almost as well as the 17mm Ethos for edge-of-field sharpness, with the XWA showing only slightly more star bloating at the very edge. I was impressed!

The XWA showed a trace of lateral chromatic aberration at the edge of the field, adding false-color fringes to star images. The field stop was sharply defined but had a blue tint to it. But that was also true of the Ethos.

When panning across the sky, the XWA exhibited only minimal pincushion distortion. When present to a large degree, this can make the sky look as if it is on the inside of a bowl, a disconcerting effect when scanning around. There was also very little “kidney-bean” darkening of the field as I moved my eye around, again similar to the Ethos.

 

The XWA’s nine lens elements are stated as being fully multi-coated (the FMC designation), which appeared to be the case. Credit: Alan Dyer

 

I saw no ghost images or errant reflections in the field when the Moon was near the edge of the field or just outside it. The multi-coatings and internal blackening did their jobs well. I also saw no imperfections such as scratches, paint flecks or dust on the interior lens elements.

Eye relief is stated as 15mm, a figure I confirmed, as measured from the top of the rolled-down rubber eyecup. This is on par with other 100° eyepieces of this focal length, and was more than sufficient for a comfortable view of the entire field without glasses on. 

But with glasses on, even with the eyecup rolled down, the whole field was not visible, which isn’t surprising with such a wide field of view.

XWA Mechanics

While the eyecup just clips into a groove around the top of the eyepiece, it remained secure and did not pop off with normal use. Even so, there’s nothing as fancy as a click-stop eyecup, as with some long-eye-relief eyepieces.

The eyecup is soft, pliable rubber that should withstand frequent rolling up and down. Credit: Alan Dyer

 

The upper barrel is wrapped in a ribbed rubber grip ring which can slide around the barrel. Perhaps with frequent use and exposure to the elements it might break and fall off, but I found no problems with it in the short time that I used the XWA.

As expected, the bottom of the barrel is threaded for standard 2-inch filters.

Love them or hate them, the XWA’s 2-inch barrel has a “safety undercut” for securing it in a focuser. Credit: Alan Dyer

 

The eyepiece is said to be sealed and waterproof, but that’s a claim I’m never willing to put to the test. My test nights were not dewy enough to get the eyepiece soaking wet to see if any moisture penetrated into the eyepiece.

The XWA’s cosmetic look is plain, but it is enhanced by two engraved silver rings around the top. Credit: Alan Dyer

 

The labeling at the top of the barrel appears to just be painted on, so could wear off with time, unlike premium eyepieces where all markings are engraved for lasting use. There’s also nothing as luxurious as the large glow-in-the-dark labels some brands offer. 

Recommendations

The bottom line is that the 20mm XWA eyepiece offers very good construction and gives spectacular views.

 

This simulates the actual field of view of the XWA 20mm eyepiece on two of the test telescopes used: an 8-inch f/6 reflector (the inner red ring) and a 94mm f/5.5 refractor (the outer blue ring). Credit: Alan Dyer

 

It provided an actual field in the 8-inch Newtonian of 1.7° at 60 power, ideal for good definition of deep-sky targets, while maintaining a “spacewalk” style field. In the 94mm refractor, the field was an even more impressive 3.9° at 26 power, great for sweeping along the Milky Way.

While I did not test the XWA on a Schmidt-Cassegrain, I know from experience that a 20mm eyepiece was my most used eyepiece on my 8-inch f/10 SCT. While the XWA would require the use of a 2-inch star diagonal, on an 8-inch SCT it would still provide an impressive 1° field even at 100 power, making the XWA a superb choice for most deep-sky viewing.

I can highly recommend the 20mm XWA for any telescope able to accept 2-inch eyepieces. At $300, the Astro-Tech XWA provides an astounding value in a 100° eyepiece.

 

PLUS

Excellent image sharpness across the field

Good eye relief

Reasonably light for the design 

Low price for a 100° eyepiece 

 

MINUS

Plain cosmetics and finish

Lacks the prestige of costly brands!

 

MSRP: $299.95
Website: www.astronomics.com

 

About Alan Dyer

Alan Dyer is an astrophotographer and astronomy author based in Alberta, Canada. His website at www.amazingsky.com has galleries of his images, plus links to his product review blog posts, video tutorials, and ebooks on astrophotography.

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