The development of the Explore Scientific 20 mm 100-degree Series Nitrogen-Purged Waterproof Eyepiece was a collaborative effort of astronomers and engineers who tested our prototypes again and again, in the field and in the factory to make refinements to produce the final production eyepiece.

Inspiration for ultra-wide field eyepiece designs came from several designers. Wright H. Scidmore patented important ultra-wide angle eyepiece designs (one with long eye-relief) in the 1960s for the U.S. government. His influence can be seen in many eyepiece designs on the market today with eyepieces of 68 to 80-degrees apparent field and more. Carl Zeiss made eyepieces of 110 and 120-degrees apparent field for use in U-boat periscopes before World War II. These are but two notable designers who developed ultra-wide field eyepieces over the decades.

Like all Explore Scientific eyepieces, the lens elements of the 100 degree eyepiece are meticulously cleaned and aligned before being installed in their precision machined lens barrels.

Each lens and lens grouping have EMD (Enhanced Multi-layer Deposition) Coatings and are edge-blackened to eliminate light scatter and maintain image contrast.

Contrast is further enhanced with baffles that mask and deflect unwanted stray light.

These eyepieces with their huge apparent field of view not only gave the observer a panoramic visual experience, but they relax the eye so the observer could pay attention to subtle details for extended periods. These ultra-wide angle eyepieces played a critical role in the military for aiming at targets, and their long eye-relief counterparts helped reduce eye injury from recoil.

Each 100-degree Series Nitrogen-Purged Waterproof eyepiece is internally sealed and purged with inert, dry nitrogen gas to prevent internal fogging, to halt the intrusion of fine particulates and fungus, and to maximize the life of the internal coatings.

To make sure, every 100-degree eyepiece is tested by submerging them down to 1 meter of water for 30 minutes.

Years later such eyepiece designs transformed the visual experience for amateur astronomers, as they started using military surplus cannon sight eyepieces on their backyard telescopes. Al Nagler with his company Tele Vue introduced his Nagler 82-Degree eyepieces (and later introduced the 100-degree Ethos eyepieces), and then other commercial telescope companies such as Meade Instruments, Pentax, Celestron, and others made ultra-wide field eyepieces specifically for use in amateur telescopes. Since extreme performance eyepieces are expensive to make, they come with a relatively high price tag over standard eyepieces.

After announcing Explore Scientific's line of telescopes at the Astronomical League Conference in the summer of 2008, we decided to focus on extreme performance, ultra-wide angle eyepiece designs as well. We wanted to offer ultra-wide angle designs in popular formats at lower prices. Now more astronomers could experience the benefits of the amazing panoramic views these eyepieces provide.

Each and every Explore Scientific eyepiece is inspected both at the factory and again at our USA facility in California.

Here we are making final visual and cosmetic inspections where we check for assembly integrity, cleanliness, and optical performance (including a test for visual image edge consistency) before shipping them to our customers.

Developing our new eyepieces we wanted to take a fresh perspective and address several points. Our goal was to produce an ultra-wide angle design that provides pride of ownership at a great value:


Focus on Value - We invite direct comparison to any eyepieces on the market in their category.

Protection from the Outdoors - By making the eyepiece body nitrogen-purged and waterproof eyepiece internal elements will remain as pristine as the day they were assembled. 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.

Creating an Identity - We look at purchasing fine optical equipment as an investment, and it should be treated as such. With a unique serial number on each eyepiece we can track when a product was made, and the owner can document their equipment for insurance and warranty purposes.

Explore Scientific 20 mm 100-degree Eyepiece Specifications:

• Waterproof: Submersible to 1 meter for 30 minutes; Nitrogen-purged to prevent internal fogging
• Coatings: All lens-to-air surfaces are full multi-coated
• Eyecup: Soft rubber folding style; Replaceable
• Weight: 2.125-pounds

• Focal Length: 20 mm
• Apparent Field of View: 100-degrees
• Eye Relief: 14.5 mm
• Barrel: 2" diameter, tapered barrel-style, accepts 2" diameter standard filters