I am using the z pro on a Canon 16-35 MKII and managed to completely eliminate the vignette problems, even at 16mm. What I did was take the four bolts out and disassembled the entire thing. I placed the adapter ring, in this case a 82mm, on the inside of the z pro assembly. In other words, instead of having the adapter ring between the lens and z pro, the z pro is now between the lens and adapter ring. I also removed one of the spacers, reducing my number of filter spaces from 3 to 2 (which is all I would ever use anyway) and then I turned the bolts backwards. I did that because after removing the spacers the bolts extend out a bit. Reversing them keeps them from jutting out into the photo. I will try to post a pic shortly.