since it´s supposed to be released along with the nex7 and a77 the only info so far is on sonyalpharumors so it´s not real as yet obviously - apparently it´s to give the same focusing speed that the a55 has to the nex mount - the mirror diverts approx. 30% of the light to another sensor just as the slt cameras do - yep, it´s to adapt alpha mount to nex and rumored price is 400us