This 8.5mm Explore Scientific LER 82° field argon-purged waterproof eyepiece is the right focal length to give you very useful exit pupil sizes and magnifications with all scope types and focal ratios - f/10 Schmidt-Cassegrains, short focal length f/6 refractors, and f/4.5 Dobsonian reflectors alike.
This 82° 8.5mm Explore Scientific LER is an excellent medium focal length/ultra wide field eyepiece 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.
The latest computer design programs have been used to optimize its performance. Its seven element/four group design uses low dispersion and high refractive index lenses and full multicoatings for high contrast, high resolution, and flat field images across a very wide 82° field of view. The lens edges have been blackened to improve contrast.
The 8.5mm 82° Explore Scientific works with any telescope, from a fast focal ratio reflector, to a catadioptric, to a long focal length refractor. With an 8" Schmidt-Cassegrain, for example, it gives you 227x, a 0.88mm exit pupil (very close to the 1mm exit pupil recommended for high magnification observing under average to good seeing conditions), and a 0.36° field of view (about three-quarters the diameter of the full Moon). With a 10" f/4.5 Dobsonian, it gives you 129x, a generous 1.95mm exit pupil suitable for nebula observing, and an equally generous 0.64° field of view (more than one and a quarter times the diameter of the full Moon). You can use the calculator in the "formula" tab above to see just how wide the field will be with your particular telescope.
At 15mm, the eye relief is surprisingly good for an eyepiece in this focal length range, although eyeglass wearers might see a somewhat vignetted image. This isn't as much a problem as you might think, as the 82° field of view is so wide that even non-eyeglass wearers have trouble seeing the whole field at once. This is an eyepiece that shows you a "picture window view" of space for a true full-immersion observing experience. With its unconstricted view, your eye relaxes, allowing you to easily use the "averted vision" technique to study faint details across a huge field of view.
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. This link will take you to full details on this unique transferable lifetime warranty.
