The 20mm Explore Scientific 100° field 2” eyepiece is O-ring sealed and nitrogen-purged to be 100% waterproof. To insure a perfect seal, Explore Scientific tests every eyepiece in one meter of water for 30 minutes before shipping.
Internally sealing the eyepiece and purging it with inert, dry nitrogen gas prevents 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.
The 20mm Explore Scientific 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 (using lenses of dense crown, light crown, dense flint, and lanthanum rare earth optical glasses) 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 Explore Scientific Explore Scientific 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 Explore Scientific 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 Explore Scientific Explore Scientific has the benefits of the higher power and darker sky backgrounds that are inherent in its shorter focal length. You can use the field of view calculator in the "formula" tab above to see just how much sky the Explore Scientific can reveal with your telescope.
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 14.5mm, the 20mm Explore Scientific 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 Explore Scientific 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.
This individually serial numbered Explore Scientific eyepiece is backedby a limited one year warranty, which will be extended to an ExploreScientific transferable product lifetime limited warranty when its warranty card is registered with Explore Scientific within 60 days of purchase.With the extended product lifetime warranty, this Explore Scientificeyepiece will be protected for as long as it continues to bemanufactured, plus an additional five years. Full details on this unique transferable lifetime warranty.