So I took the plunge and bought the VW-W4607H-K. It's a great lens and there's no vignetting when using just the lens, but if I put a filter in between then there is a little vignette.

Is there any way to attach a hood while using the lens? It doesn't seem like it's meant to have a hood on the lens since there is no threading.

I just shot with mine today. It's not designed to have a filter in front of it or behind it. The lack of threads on the front make it completely obvious that it's not designed to take a hood. Both of these facts are clearly stated in the instructions that come with it.

Always remove filters when you fit a wide-angle converter. That's because you're reducing the focal length and consequently increasing the depth of field, so any imperfections on any of the glass surfaces in front of your camera's front element are more likely to be in focus. And - as you've found out - vignetting is much more likely when you use filters.

Extra elements always up the flare levels too, so if you can find a clamp-on hood (I doubt that you will though) it's always a good idea to fit one.

tom.