Leica 21mm f/3.4 Super-Elmar-M ASPH Includes a metal, screw-mounted lens hood to prevent flare effects and ensure perfect image sharpness. The sophisticated optical design and construction of the lens comprises eight elements - including one with two spherical surfaces and another four with anomalous partial dispersion. The sophisticated optical design and construction of the lens plays a decisive role in reducing distortion and vignette to an absolute minimum.