I agree that the Werra cameras are a beautiful (and slightly quirky) design. The tessar and flektogon lenses have an especially nice character to them. The flektogon lens can vignette slightly with the prestor shutter so even if you managed to engineer a mounting solution you could find that a problem with an even wider lens. The lens is mounted in front of the shutter unit and I would think this could be the cause of the the vignetting problem. Also the rear lens element must not protrude too far back to interfere with the shutter.