This 4×5.65 carbon fiber matte box is designed to attach to the lens itself instead of onto the camera’s rail system in order to be as lightweight and unobtrusive as possible. However, it comes with an optional 15mm rail attachment if you wish to attach to the rail system. It also comes with several different sizes of lens adapter rings to fit most front diameters of lenses. These adapter rings not only allow the matte box to directly attach to the lens itself but it also forgoes the need for lens donuts. Included in the package is one top French fag to provide flare protection.