Most old lenses have optics in groups that can be removed very easily. In this particular lens, it has the front and the rear group. Despite the different looking lens barrels, the optical element groups are identical in both lenses. Took the optics out from the Exakta mount lens, and put them in the M42 lens barrel. Works beautifully.
The lens itself isn't too bad. In fact, it's quite nice. A bit slow with the f2 maximum aperture, but can't complain about the cheap price of $5.
Left shows dismantled Exakta mount of the lens, right shows the transplanted M42 version
Street Crossing - NEX-6 & Isco-Gottingen Westagon 50mm f2. Click for larger.
Umbrella - NEX-6 & Isco-Gottingen Westagon 50mm f2 @ f2.8.