See link below.... there may be a revised (well another choice) ART 50mm coming... in an image sense this may be the OTUS 55mm / Leica 50mm APO killer... but certainly not in build quality. 
With "Fluorite similar" glass qualities... i heard a whisper of this a few months back and seen this link recently also.
http://egami.blog.so-net.ne.jp/2015-07-17
With "Fluorite similar" glass qualities... i heard a whisper of this a few months back and seen this link recently also.
http://egami.blog.so-net.ne.jp/2015-07-17
