Multicoated, aspherical eyepiece lenses and BaK4 prisms Deliver bright, high-resolution images under all lighting conditions. Generous eye relief For a clear and comfortable view, especially for eyeglass wearers. Includes turn-and-slide rubber eyecups. Fully waterproof/fogproof Nitrogen-filled and O-ring sealed. Smooth central focus knob Fast range of focus for quick viewing. Durable and protective, rubber-armored coating Provides a sure, non-slip grip, wet or dry.