Nobody has mentioned so far that the A77 doesn't have an optical viewfinder. As far as I can make out you look through the viewfinder and you see an image on the OLED screen. The semi-transparent mirror is used send an image to the autofocus system. It's more like a bridge camera than a classic DSLR.

This is not a criticism. Sony are being original. Lets see how it works out in practice.