I forgot to mention that I'm including a super cool, 21mm shade that I found on Shapways. It was designed for the newer 35mm Ultron Vintage Aspherical type II. The 21mm f/3.5 and the Vintage 35mm share the same Voigtlander lens hood. When I asked the designer of this super compact hood, he thought there might be cut off but placing the camera into bulb and looking through the back of the camera, I'm not seeing any physical vignetting with the lens wide open.
It is super compact, just perfect for the lens. The only drawback is the front lens cap does no longer fits inside the hood. For me its a worthwhile trade-off.