The hoodman hoodmag 30 is designed to replace the standard eye cup that comes with the hoodloupe 30 lcd screen magnifier not included hoodmag has a tighter fit than the original eyecup and will stay in place once mounted while providing 30x 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