It's a great lens on the D7100, I have it.
The ultra ultra wide angles like the Tokina are a different animal altogether and have a definite learning curve. For example, if I'm shooting a sunset but the clouds are only on the horizon then a wide angle is not what I would use due to how far away everything is pushed. But, if I have clouds/color that is rising up and wrapping back to to me this is great for the lens. The point, it's pretty easy to fill the lens from side to side, but the vertical axis can at times be difficult. And you want to have the camera held level or as you tilt up or down it will curl the corners of the shot (however it can be a cool effect). I am not trying to dissuade you from the lens. Simply sharing the excellent information that was shared prior to my purchase and my crash course learning curve on a very wide angle lens.