Canon EF-EOS R Drop-In Filter Adapter with Drop-In Variable ND Filter ADrop In Filter Mount Adapter EF EOS R takes the functionality of Mount Adapter EF EOS R and adds the ability to use drop in filters, removing the need to fit filters on the front of a lens, especially useful for wide angles with a large front lens element. Its available with either a variable neutral density (V ND) filter or circular polarising (C PL) filter, and a clear (CL) filter is also available for shooting without filter effects.