Interesting idea. Kind of expensive, tho...http://www.metabones.com/info/105-info/ ... ed-booster
Speed Booster™, which mounts between a mirrorless camera and a SLR lens. It increases maximum aperture by 1 stop (hence its name), increases MTF and has a focal length multiplier of 0.71x. For example, the Canon EF 85mm f/1.2L II lens becomes a 59mm f/0.9 lens on a Sony NEX camera, with increased sharpness. The faster F-stop allows for shallow depth-of-field and a lower ISO setting for decreased noise.
It will be available in January 2013 from Metabones' web site and its worldwide dealer network for US$599 plus shipping and applicable taxes and duties.