A few days ago I received my copy of the Rokinon 12mm f2.0 for the Fuji x-mount. I spent some time over the weekend taking a look at it, so here is my take at a first look.
Overall distortion is low, easily corrected if need be, probably won't notice it in a lot of shots.
distortion is pretty well controlled for an ultra wide in the price range.
Soft at f2 but get better at f2.8 and beyond. Corners much better at f5.6
Vignetting at f2, like I expected and it cleans up well at f4 and mostly gone by f5.6
Smooth focusing and half stop detents from f2 to f22
Slightly smaller the Fuji 14mm f2.8
My copy seems to have a yellowish cast in part of the image in the center area, not visible in all circumstances. I am thinking this may be a coating issue but still investigating. It is not a raw conversion artifact, it was visible in the viewfinder. I will probably return it and try another copy after I run some more tests.
It looks like a nice lens, especially for the price, but I would not replace my Fuji 14mm f2.8 or 10-24mm with it.
Some more details and samples can be found here:http://www.aps-photo.com/2014/04/rokinon-12mm-f2-0-for-x-mount-a-first-look/
Thanks and hope you find this useful.