The long 300mm telephoto lens at a distance of 1,000-Feet (300m) provides 21-Feet (6.5m) horizontal scene size when used with 1/2-Inch sensor camera. This lens system with F3.75 aperture provides high image quality in all usable light conditions. This model also features heavy duty design and build specifically developed by Marshall for use in law enforcement, military, and covert surveillance needing crystal clear viewing at long ranges.