The M4 filter holder allows for the use of a magnetic graduated ND filter that is more convenient than a traditional screw-in grad filter by allowing you to adjust the grad filter within the filter frame. With the M4 holder you get all the advantages of a traditional drop-in graduated filter without the need for the larger filter holder system. The grad filter can be adjusted vertically to better balance light in your image, and can also be rotated within the holder to help you get the perfect shot!