Well, fwiw I have both lenses and prefer the 7-14. It requires the 6" port so if packing space is critical that could be an issue, but overall I like the extra FOV and feel it is a bigger difference than it might seem just looking at numbers. I also feel the lens is a bit sharper, but if so it is probably all but insignificant. Sometimes I think the 7-14 is a a little weak in the corners, but am not sure if that is the lens or the port and it is a small thing. Generally I am not using it for shots where corner sharpness is critical and if the corners are water or sand or dark it doesn't matter and corners can also be cropped easily. The 9-18 works in the Nauticam 4" port. I have not yest used the Zen 100mm. I don't know if it matters to you, but the 9-18 also overlaps the FOV of the 12-50 quite a bit and both those lenses can be used in the same port.
The minimum focus distance on both is the same. I am not that fond of either for CFWA; I think the 8mm is much better for that.
I like my 8mm fisheye better, but the 7-14 is a lens I am reluctant to leave behind and I typically only use the 9-18 as an above-water travel lens. The extra FOV of 7mm is the big deal for me. I am not sure, but I might use the 12mm Oly lens before the 9-18...I don't have the 12mm yet so I don't know how noticeable the extra sharpness and speed are underwater.
Edited by Draq, 03 June 2013 - 09:47 AM.