This variable ND filter has been designed for use with the Canon Drop-In Filter Mount Adapter EF-EOS R and is an elegant solution for using a neutral density filter with an adapted lens—especially when the lens does not have a conventional filter thread. With an integrated wheel, you have the ability to adjust the strength of the filter as needed. A neutral density filter (ND filter), or gray filter, blocks a portion of the incoming light. By using a gray filter, you can significantly extend the exposure time, achieving effects such as blurred water or preventing overexposure of the image in bright midday sunlight with an open aperture.