[Sylvain]

I own the 9-18 and it's quite a pleasant lens. It's a nice performer but I'm sometimes skeptical about its retracting construction, some play appeared over time. It doesn't seem to have a visible effect on IQ but I still wish it had a conventional construction. Other than that, lightweight, silent, really nothing to complain about. 9mm is wide enough for me because I still don't have proper 12-xx lenses (the 12-35 doesn't have a wide enough range for my taste and the 12-50 is totally unimpressive optically). If you would end up owning the 12-35, I'd probably think it's not worth swapping to a 9mm lens.