Canon Drop-In Filter Mount Adapter EF-EOS R with Variable ND Filter ACanon Drop In Filter Mount Adapter EF EOS R with Variable ND Filter A Drop 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. It's available with either a variable neutral density (V ND) filter or circular polarising (C PL) filter, and a clear (CL)