The Haida Square Filter Holder allows you to use 100mm square filters as opposed to traditional screwtype circular filters. These filters are compact and easy to store in the side pockets of your camera bag, so you can bring more to every shoot. The holder has 3slots so filters can be stacked to create a stronger effect (especially when used with neutral density filters). The HD2500 fits lenses from 77mm-82mm with the use of Haida’s metal adapter ring (sold separately). Square filters are also available in a variety of types, including Circular Polarising and Neutral Density.