Rokinon Samyang also supposedly now have a 10mm for the x mount. I am trying to find out more about this lens as it's $529.00 F2.8.
Has a big outer element, won't be filter friendly.
Paul the Samyang 10mm is one of their APS c dslr lenses with a mount adapted. Big and heavy. Their 12mm looks like it was designed for the mirrorless cameras. I have heard they will start shipping mid April, that is at least according to B&H even though they had an earlier date. It also looks like Samyang redesigned their fisheye 8mm and added another element and ED glass.
I have heard a lot of good things about the 10-24mm from fuji.