Marathon 10x50mm BAK-4 Prism Binocular Black. The default focus distance setting is 70 feet (dependent on the user's eyesight). 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 10x50mm BAK-4 Prism Binocular: Manufacturer: Marathon Color: Black Magnification: 10 x Objective Lens Diameter: 50 mm Prism Material: BAK-4 Eye Relief: 0.7 in Exit Pupil: 7.1 mm Field of View Linear: 342 ft at 1000 yds Optical Coating: Fully Coated Binoculars Focus System: Fixed/No Focus Weight: 1.5 lb Package Type: Box Package Contents: Marathon 10x50mm BAK-4 Prism Binocular Marathon BI030029: 10x50mm BAK-4 Prism Binocular Black