I am wondering what the best choice would be for me. I already have a Nikon 14-24, so I was wondering whether I should get both an adapter and a Speedbooster giving me two lenses in one: a 14-24 f.28 with phenomenal optics as well as 10-17mm f2.0. The disadvantage of course is the size. The Sony 10-18 is the most economical and comes in a small size, but at f4 it's two stops slower than the 14-24 plus Speedbooster. The Zeiss is in the middle: faster than the Sony, but not as fast the Nikon. It's least flexible at a fixed 12mm, which I do not find to be a very frequently used focal length.