Explore Scientific 20mm 68 degree Series Argon-Purged Waterproof Eyepiece. This eyepiece by the professionals at Explore Scientific uses advanced computer design combinations of low dispersion and high refractive index optical glasses and durable multilayer deposition coatings. The Explore Scientific 20mm 68 Series Hyper-Wide Argon-Purged Eyepiece is impervious to internal fogging and contaminants such as fungus growing in between the lens elements. With a long eye-relief and a 68 apparent field the Explore Scientific 20mm 68 Series Ultra-Wide Argon-Purged Eyepiece let's you enjoy your viewing experience for a longer period of time. Specifications for Explore Scientific 20mm 68 Series Ultra-Wide Argon-Purged Waterproof Eyepiece: Focal Length: 20mm Length: 69.6mm Width: 50.3mm Weight: 8.7oz; 247g Barrel Size: 1.25" Eye Relief: 15.3mm Field Stop Diameter: 22.8mm Package Contents: Explore Scientific 20mm 68 Degree Series Argon-Purged Waterproof Eyepiece 68 Series 20mm Argon-Purged Waterproof Eyepiece; 1.25-inch O.D.