The Voigtlander Ultron 21mm F1.8 ($1,149) captures an ultra-wide field of view when paired with a full-frame rangefinder or mirrorless camera, and also manages to capture a lot of light. When set to its f/1.8 aperture, its center sharpness is excellent with some softness at the edges of the frame. It can also lock on to subjects just a half meter (about 20 inches) away, which makes a shallow depth of field possible. When stopped down, the edges sharpen considerably, which is a must for landscape shooters. Its an excellent value, especially when compared with the $7,650 Leica Summilux-M 21mm f/1.4 ASPH. The Ultron ($1,149.00 at Amazon) can focus as close as 0.5-meter, which is beyond the 0.7-meter capability of most rangefinder cameras. If you're pairing it with the Leica M (Typ 240) ( at Amazon) you can use an EVF or Live View to confirm focus when you move in closer, and you won't have any concern about the limitation when using a camera with full-time Live View like the Sony ...
The Voigtlander Ultron 21mm F1.8 is a wide-angle lens that captures a lot of light, but you'll have to stop down for edge-to-edge crispness.
Wide-angle field of view; Wide aperture; Focuses to 0.5 meter; Excellent build quality
Some edge softness at wider apertures; Noticeable color fringing; Big for a rangefinder lens