Astro-Tech 20mm 100° field waterproof XWA 2" eyepiece


Availability: In stock

The 100° apparent field of the Astro-Tech 20mm waterproof 2" eyepiece provides superb maximum field/medium power observing in all scopes, from small apo refractors to the largest Dobsonians and catadioptrics . . .
Our Product #: ATXWA20
Astro-Tech Product #: ATXWA20

Product Description

The 20mm Astro-Tech eyepiece, has high contrast, comfortable eye relief, and full field sharpness - with well-controlled astigmatism, field curvature, and lateral color. Its nine element optical system is designed for maximum field/medium power deep space use with telescopes having focal ratios down as low as f/4. It is exceptionally effective on nebulas with fast f/ratio reflectors, such as Dobsonians, as it gives both an immense field and a bright exit pupil (almost 4.5mm with the typical f/4.5 Dob). Its very wide field also makes it convenient for moderate power lunar and globular cluster observing with Dobsonians, as you have much longer to observe before the planet drifts out of the field and the scope has to be repositioned than you do with a 60° or 70° (or even 82°) field eyepiece. In addition to Dobs, the new 20mm Astro-Tech is marvelous for observing open clusters, nebulas, galaxy clusters, and globular clusters with any telescope capable of using a 2" eyepiece.

The 100° apparent field of this new 20mm Astro-Tech eyepiece is nearly 50% larger in area than an 82° field eyepiece. You could get a similar true field with a longer focal length (but narrower apparent field) conventional eyepiece, but the 20mm Astro-Tech has the benefits of the higher power and darker sky backgrounds that are inherent in its shorter focal length.

The 20mm Astro-Tech 100° field 2" eyepiece is O-ring sealed and to be waterproof.  While waterproofing might seem important only for observing underwater, waterproofing serves several useful purposes for the astronomical observer as well.

Internally sealing the eyepiece helps prevent internal fogging in the eyepiece when observing at sub-freezing temperatures. For observers in dusty climates, sealing keeps wind-blown dust and fine particulates from getting into the eyepiece body. For observers in very humid climates, sealing prevents the growth of fungus on the internal lens elements. For all observers, complete sealing maximizes the life of the internal optical coatings and makes the eyepiece easier to clean, as there is no risk of cleaning solution migrating from the top of the lens and seeping around edges to be trapped in between elements.

There is a soft rolldown eyecup to shield your eye from ambient light (from a neighbor's security light, for example) and improve the image contrast. With an eye relief of 15mm, the 20mm Astro-Tech would normally somewhat vignette the field of view for eyeglass wearers. However, since the 100° field is so wide that you can't see the full field without having to move your head from side to side to take it all in anyway, vignetting in the conventional sense is not a problem.

The 20mm Astro-Tech fits 2" focusers only. A safety groove is machined into the 2" chrome barrel to engage your focuser thumbscrew. This helps prevent the eyepiece from falling should the thumbscrew accidentally loosen while observing.

Tech Details

Barrel Size 2"
Eye Relief 15mm
Field of view 100
Focal Length 20mm
Number of optical elements 9
Weight 24 ounces/690 grams
Warranty 1 year


Review by:
With my Fast 100mm F4.5 Achro RFT I did a side- by- side test with the Astrotech XWAS 20mm 100 degree and a 23mm Celestron Luminos 82 degree . First surprise was that the Astrotech required about 3/4 inch more in travel than the Celestron. My daylight target was a brick building 50 yards distant The math said the Astrotech would have a 6% increase in FOV over the Celestron, however the FOV was the same. The main difference was that the Astrotech had much better edge correction probably due to its 9 elements over the Celestrons 6. In addition it provides a 15% increase in magnification while reducing the exit pupil 12% which is great for my Bortle 7 skies. Final comment great build and optical quality at a fantastic price. (Posted on 4/1/2022)
Review by:
Orion nebula, M42, Trapezium 4 stars were looking good at 75x, nebula clouds visible, 12" dob, 1500mmFL. Maybe stars at edge of view were at a different focus, but my quick use tonight was not with a perfect sky. Just nice to roll down the eyepiece cup, put my glasses up to it and fall into the star field. (Posted on 1/30/2022)
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