This is a Kenko filter adapter ring (for 77mm diameter lenses) and a "100x125mm HALF ND PRO 4X" half ND filter. Purpose: To attach to a lens to prevent unwanted light from entering, suppressing flare and ghosting, and to use as an adapter for attaching filters. Size: Can be attached to lenses with a 77mm lens size. By replacing the inner ring, it can be applied to various lenses.