The phot r grey camera lens filter for the gopro hero 4 3 and 3 attaches on to the dive housing of the hero 4 3 and 3 the main use for grey filters are for blurring water motion eg waterfalls rivers and oceans reducing depth of field in very bright light reduce the visibility of moving objects and to add motion blur to subjects solid colour filters are designed to enhance natural light with subtle colour wash or bold strong effectbr the filter snaps into place for quick tool free