Features : Stack multiplier on top of SMC to get much more magnification wihle shorter working distance. Providing 3.5X magnification when using a 100mm/105mm macro lens on a full frame camera. Needed accessor to work with SMC: 81211 Flip holder for Multiplier I Uncompromised Optical Quality The multiplier is constructed from lenses are precision crafted of specially formulated low dispersion optical grade glass, ground to the most demanding standards. These exceptional measures, enhanced by broadband anti-refective coatings effectively reduce common optical issues such as chromatic aberrations, coma, spherical aberration, and field deformation associated with underwater macro photography using traditional magnifying lenses. These optics are assembled in a rugged hard anodized aluminum housing, and nitrogen purged during assembly to eliminate fogging.