As an aside, the other reason I'll not use the Carrara built in refraction is shown above. Even though this globe has thickness and is hollow in the middle, Carrara renders it as a solid, like a marble. Now we've all seen big fish bowls or terrariums with plants in them and know that the distortion is only on the sides of the globe. Consequently, I just eliminate the refraction and engage the other features of fresnel with the tools described above. Personal preference. :)