ED glass for optimum clarity. Dielectric coatings provide increased light reflectivity. Fully multi-coated optics to produce sharp images. Focus knob with 1.5 turn - close focus 6.6 ft. High resolution phase corrected BAK-4 roof prisms. Water repellent coating on objective lens. Lightweight rubber coated magnesium alloy chassis. Stay-on lens covers for maximum lens protection. Replaceable twist-up eyecups with position stops.