Sony NEX DSLR via Leica Visoflex
Sony NEX-3, Leica Visoflex I, and a Leitz 280mm/f4.8 ver.2 Lens
Here is NikonD200 's Sony NEX DSLR with the use of the Leica Visoflex I from 1956. The Visoflex is attached to the NEX-3 using a Leica M to E-mount lens adapter.
Below shows how a Leica bellows can be used for macro shots using the NEX and the Visoflex.
Sony NEX-3, Leica Visoflex I, Bellows I and a Leitz 280mm/f4.8 ver.2 Lens
The focusing and composing is done through the Leica Visoflex viewfinder. A lever flips up the mirror and then hits the shutter release button.
Leica Visoflex in Action
So if you are looking for a viewfinder for your NEX, hunt down a Leica Visoflex.
Pictures from NikonD200 and video from Lowcomotive.