You absolutely do NOT want to use a FX fisheye on a DX camera. The fisheye effect is mostly gone in that constellation. You'll just have a 24mm lens with strong distortion, but not really much of a fisheye effect. But the other way around works nicely, especially if you also circumcise the 10.5mm DX. Then you *almost* have a circular fisheye. Plus the DX fisheye is cheaper than the FX fisheye. Plus if you cut the fisheye potion out and leave the black borders out, you can use 1:1 format instead of 3:2 which makes the fisheye effect even more visible. Plus of course fisheye lenses dont really have that much resolution in the first place, so thats not really that much of a loss either. Thats also the cheapest way to get a fisheye. Since I'm not sure how often I will even be using this specific effect, I have prefered this option.