Key features of the new Leica APO-Summicron-SL 50mm f/2 ASPH include 12 lens elements in 10 groups, and dust/moisture resistance. As Leica is part of the L mount alliance it will also be compatible with relevant Sigma and Panasonic cameras. A snip at £3,750 from authorised Leica dealers.
If nearly four grand seems a bit steep, Chinese maker 7 Artisans has announced a 75mm f/1.25 Leica M-mount lens for a more manageable £369. The lens, shown above, is manual focus only, with a 13-blade aperture, multi-layer lens coating to supress flare and boost contast. and an 80cm minimum focus distance. More details here.