The SMB-1 is a large studio matte box, it is designed for bigger wide-angle prime lenses, as well as zooms.
The SMB-1 covers the full ALEXA sensor area and allows the Master Prime 12 mm to be used with a 2-filter-stage, the Ultra Prime 10 mm with a 1-filter stage, and the Ultra Wide Zoom UWZ 9.5-18 mm with a 1-filter stage.