This Rear Filter Adapter Ring for Select Sigma Art Lenses for Canon EF from Haida allows select Haida filters to be installed behind the rear element of a lens that doesn't have traditional filter threads on the front end. Simply remove the existing rear ring from the lens using the included mini-screwdriver, then install this precision engineered aluminum adapter ring is installed in its place. Then the corresponding filters made to fit the adapter ring can be easily installed when needed and removed when finished. Once this rear filter adapter ring is installed there is no reason to remove it, it may be left in place indefinitely without affecting the operation or performance of the lens.