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) filter is also available for shooting without filter effects.