52° 25mm Waterproof Eyepiece

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.

Long considered the "standard" eyepiece that is often supplied with telescopes that are sold by various suppliers, the 25mm focal length category is perhaps the most used eyepiece in the world. Like the 20mm, these eyepieces are great for binoviewer devices, and the 25mm is probably the longest focal length of the mid-power range eyepieces before you get into longer focal lengths. 

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.