The angle finder is an attachment to the 645 AFD prism. You must rotate the camera to change the format but the angle finder rotates so that you are still looking down into it. See it here -http://www.mamiya.com/products2.asp?id=1&i...4=2179&id5=2180
that same angle finder device is available for Contax 645. (and other contax)
I have one.
nicely made, fits over the reflex viewer.