Leica Summilux-M 21mm f/1.4 ASPH.

Technical details
The Summilux-M 21mm f/1.4 ASPH. consists of ten lenses in eight groups and incorporates five separate lenses with anomalous partial dispersion. As a result, vignetting and distortion are both excellently corrected. The floating element retains the lenses’ high resolution, even in the close-up range. A patented, rectangular lens hood fits Series VIII filters.