If you have room in your observing kit for only one long focal length wide angle eyepiece, this Explore Scientific 40mm argon-purged eyepiece may well be the one eyepiece for you.
This new 68° 40mm Explore Scientific is a high-quality and physically-impressive low power wide field 2" eyepiece for the serious deep space explorer. It comes with an unusual benefit. It is O-ring sealed and argon-purged to be 100% waterproof. This prevents internal fogging in the eyepiece; keeps the interior dust-and fungus-free; and makes it easier to clean, as there is no risk of excess cleaning solution getting trapped between the lenses.
Many observers feel that a 68° field eyepiece like this Explore Scientific hits the "sweet spot" between the affordable, but "looking down a tube" view of conventional 45°-50° field eyepieces, and the full-immersion, but very expensive, observing experience of an ultra-wide field 82° or 100° eyepiece.
Because of its long focal length, the 2" 40mm Explore Scientific is at its best with telescopes having a focal ratio of f/6 or longer (an f/6 scope gives it a 6.67mm exit pupil, about the largest most observers can fully utilize). A shorter focal ratio will waste some of your scope's light gathering capacity when used with the 40mm Explore Scientific. If your scope's focal ratio is f/6 or above, however, this wide field eyepiece can give you some truly excellent "big picture" views of deep space. It is ideal for observing galaxy clusters, large emission and reflection nebulas, and nebula remnants - no matter what your telescope type, as long as your telescope has a focal ratio of f/6 and longer. You can use the calculator in the "formula" tabe above to see just how wide the field will be with your particular scope.
With a huge 31mm of usable eye relief, the six lens/fully multicoated 40mm Explore Scientific can be used by eyeglass wearers with no vignetting of the field. The eyepiece has a soft fold-down rubber eyecup and comes with dust covers for both ends of the eyepiece.
This individually serial numbered Explore Scientific eyepiece is backed by a limited one year warranty, which will be extended to an Explore Scientific transferable lifetime limited warranty when its warranty card is registered with Explore Scientific within 60 days of purchase. Here's a link to the full details on this unique transferable lifetime warranty
