Adding a big lens plus an electronic viewfinder onto a NEX camera body gives you one odd looking camera rig, although having the capacity to use your present collection of lenses onto a brand new mirrorless camera really is a big whopping deal with any luck, Canon and Nikon will come up with a similar adapter if they announce any mirrorless cameras shortly). The price on the LA-EA2 may be around $400 when it becomes available in November.
The LA-EA2 allows you to mount the big Sony Alpha SLR camera lenses onto a tiny NEX camera. This usually only involves not much more than creating a connecting tube with the proper fittings for lens to body. Sony’s smart move was to add a translucent mirror there to suck up a small amount of
illumination from the image going to the camera, which is then transmitted onto a phase-detection AF image sensor in the adapter base.
Consequently, you get fast, DSLR-speed focusing from a small, mirrorless camera. Typically the contrast-detection autofocus employed on a mirrorless camera is pretty darn slow by comparison,
particularly when using a lens not designed with the camera in mind. And of course, technically the camera is no longer "mirrorless" anymore, if you want to get picky.
This type of mirror, labeled a "pellicle" mirror was used in the 1960s cameras, is the identical type Sony already puts in its A55 and A33 camera bodies, so it's already been tried and proven. It really is a very clever idea to install into a lens mount adapter. It appears so obvious now that you think about it.