Metabones + Dr Brian Caldwell announced their new "Speed Booster",
actually a well known principle from astronomy, a focal reducer or telecompressor.
See here: Metabones - Metabones and Caldwell Photographic introduce Speed Booster
White Paper is here: http://www.metabones.com/images/meta...te%20Paper.pdf
Test is here: An adaptor which claims to make your lens, faster, wider and better!! This is NOT an April Fool’s! | Philip Bloom
Done that before for my sort of photography, see on my BLOG: Photography of the Invisible World: Search results for reducer
overall system changed from f4 to f1.6 and the focal length from 84mm to 34mm!