I have the 16-35. When I took some test shots I was a little disappointed in the corners. However when I actually took it out and used it I felt a bit better about it.
However, I had a 21mm CY distagon on a 5D in the past and as I remember it, it was a bit better than the 16-35. There isn't much out there in terms of comparing the 16-35 to anything else because, I suppose, it can only be shot on a sony and most of the high powered testers don't shoot sony.
I'm sure others, have shot both lenses as well. What are your observations? The advantage I see to the distagon is a bit less weight and a bit better resolution. The zoom of course has that zoom advantage but it is heavier and with the 21mm I could do the zooming with my feet if necessary.
The zf (not the zf.2) looks like it would be a fairly easy conversion since the register on the nikon is a bit longer and there are no electronics. It looks like the lens flange sits on top of the aperture ring and is not essential to its functioning as it is on the cy models. They are available from B&H for 1,490 right now which means I would be out of pocket around 2-300 dollars depending on how much I could sell the 16-35 for.
So what do those of you who have shot both think?