Marathon NSN 8x40mm BAK-4 Prism Binocular Black. This model features a center focus with independent right ocular adjustment. Engineered with a premium BAK-4 prism it offers an excellent viewing experience with superior light transmission and less peripheral light being lost due to internal reflection. Specifications for Marathon NSN 8x40mm BAK-4 Prism Binocular: Manufacturer: Marathon Color: Black Magnification: 8 x Objective Lens Diameter: 40 mm Prism Material: BAK-4 Eye Relief: 0.7 in Exit Pupil: 7.1 mm Field of View Linear: 435 ft at 1000 yds Optical Coating: Fully Broadband Multi-Coated Binoculars Focus System: Center Focus Weight: 2.3 lb Package Type: Box Package Contents: Marathon NSN 8x40mm BAK-4 Prism Binocular Marathon BI030019: NSN 8x40mm BAK-4 Prism Binocular Black