52° 40mm Waterproof Eyepiece

Features Using advanced computer design, combinations of low dispersion and high refractive index optical glasses, and durable multilayer deposition coatings, Explore Scientific 52° Series Argon-Purged Waterproof eyepieces are optimized to produce high contrast, high resolution, and superior flat field characteristics. The 52° Series eyepieces are par-focal (meaning they focus at near the same point regardless of the focal length you select) and come with a removable and foldable soft silicone rubber eyecup for the comfort of the observer, and as experienced astronomers know, eye comfort is critical when trying to observe at the visual limits of the telescope. Protection from the Outdoors - By making the eyepiece body Argon-purged, the waterproof eyepiece internal elements will remain as pristine as the day they were assembled. Argon atoms are larger than that of Nitrogen and therefore they are less likely to leak or diffuse their way through the seals over the life of the eyepiece. The atomic radius of Argon is larger than Nitrogen by 0.13 angstroms and has a larger atomic volume by 11.2 cubic centimeters/molecule. Argon also has superior inertness vs Nitrogen (i.e. forming few or no chemical compounds with other elements) that prevents adverse reactions with eyepiece components and therefore extends the longevity of the internal components, and also prevents chemical reactions with other elemental contaminants that may be introduced through a weakened seal. And, finally because Argon is less conductive of heat than Nitrogen, Argon cools slower thereby buffering the effects of rapid temperature changes of the optics. The sealed, dry environment is impervious to internal fogging and contaminants such as fungus growing in between the lens elements. Our waterproof eyepiece is easier to clean, and there is no risk of cleaning solution migrating from the top of the lens and seeping around edges to be trapped in between elements. To insure a perfect seal we test every eyepiece in one meter of water for 30 minutes. The longest focal length in the 52° Series with the longest eye relief, the 40mm is also the only 2.0-inch O.D. eyepiece in this series. Explore Scientific now has three 40mm eyepieces in its collection, the other two are the 40mm 62° Series, and the 40mm 68° Series. At this focal length, this eyepiece is generally reserved for deep sky observers who challenge themselves to observe near the faintest observable limit of their telescopes. The huge true field of view is perfect for deep sky objects like the Andromeda Galaxy, the Rosette Nebula, as well as large star clusters, and comets. Explore Scientific Waterproof Eyepieces - Comfort, Quality, Value. The Explore Scientific 52° Series eyepieces are excellent flat-field multi-element oculars that can transform your visual astronomy experience. With an apparent field of view of 52 degrees, these eyepieces offer incredible value in a very nice eyepiece. Expect exceptional quality, eye relief and value versus a comparably priced Plossl.  Another great benefit of these eyepieces is the excellent contrast and ease with which you can gaze, not directly at an object, but slightly to either side. This skill, called using averted vision, is especially helpful when observing faint objects, because using averted vision puts the image on a part of your eye that is more sensitive to light, allowing you to see fainter images. Specifications Description 40mm 52° Series Argon-Purged Waterproof Eyepiece Item Number EPWP5240-01 Focal Length 40mm Length 96,6mm Width 61.8mm Weight 385.5 grams; 13.6 oz.  Barrel Size/Type 2.0? O.D. / Double Taper Eye Relief 27.1mm Field Stop Diameter: 36.3mm Coatings: EMD (Enhanced Multi-Layer Deposition) on all lens-to-air surfaces Lens Elements/ Groups 4 Elements in 2 Groups; Edge Blackened Filter Thread Fits Standard 2.0-inch Dia. Thread in Filters (48mm x 0.75mm) Waterproof O-Ring Sealed Argon Gas Purged; Tested Under 1 Meter of Water for 30 Minutes Eyecup Removable Flip-Down Style Soft Silicone Rubber Lens Caps Slide-on Top and Bottom Materials Optical Glass; Aluminum; Steel; Silicone Rubber Markings Laser Engraved: Focal Length; Series; Serial Number; Brand