Leica 21mm F2.8 Elmarit  Asph. The Widest Lens in the Leica M Lineup Superb Correction with Virtually No Distortion Very 3-Dimensional Images Super Wide Persepctive of 92 Degrees Accessory 21mm Viewfinder is Required The Best 21mm Lens that Leica has ever Produced   9 Elements in 7 Groups 1 Aspherical - 3 High Refractive - 2 with Partial Anomalous Dispersion Less Vignetting than any other 21mm lens, vignetting totally absent by F5.6 Filter Size is 55mm Snap on Hood & Cap included Apertures from F2.8 to F16 with clicks at half stops Focuses from .7 Meter to Infinity Only available in Black Super Wide Perspective, Great for Buildings, Architecture, Interiors, Scenics with Pronounced Foreground Subjects, Street Scenes & Photojounalism