The Polar Pro Iris filter system allows you to attach various gray filters to the camera of your iPhone. The filters are suitable for iPhone 6, 7, 8 and X and the plus models. You place the filter holder on your iPhone. Put the filters in the holder. This set contains an ND8, ND16 and ND32 filter. The ND8 corrects 3 stops, for example you use during the golden hour. When it is half cloudy and there is shade, use the ND16. This filter corrects 4 stops. The ND32 corrects 5 stops for sunny days.