The popularity of the National Geographic 8x42 Roof Prism Binocular is due to its large aperture that produces bright images and high resolution, enough magnification for serious nature studies and spectator sports, in a comfortable to hold roof prism design. Use the large rear wheel to keep your feathered friend in focus, and observe his behavior in crystal clarity through the coated BaK-7 lenses. Extended bird-watching sessions in the wild are a breeze, thanks to the lightweight, water-resistant body and lanyard to keep the binoculars at your fingertips while you hike through the brush.