The Hoodman HoodMAG 3 is designed to replace the standard eye cup that comes with the HoodLoupe 3 LCD screen magnifier (not included). HoodMAG has a tighter fit than the original eyecup and will stay in place once mounted while providing 3.0x magnification. The slip ring mounted within your HoodMAG eyecup will allow diopter adjustment without rotating the eyecup. Diopter adjustment remains the same, just twist the HoodLoupe viewing end in or out to set for your vision.