Canon - V-ND Drop-In Filter Mount Adapter EF-EOS Rhttps://photocineshop.com/en/products/CANON-V-ND-Drop-In-Filter-Mount-Adapter-EF-EOS-R-OINCQU?cat=764
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.
Neutral density filters help control the amount of light entering the camera which is useful for filmmakers looking to shoot with wide aperture/slow shutter speed combinations in bright light. It also lets landscape photographers use slower shutter speeds to blur movement in skies and water.