Here's an interesting problem. I have a glass dome which I wanted to have the image of the universe not necessarily reflecting but coming off the glass surface as if it's in there. Now I created a number of tests with materials and even followed the advice here somewhere of putting the image through a luminance channel and so on. I wanted the black of the universe image become transparent so that you could see what was going on inside as well. Well that didn't work. I even alpha channelled the image so the the black disappeared but it still looked wrong as it didn't have that "inside a glass" feel to it.
So then I found a nice solution which was to put the image through the environment channel. It worked beautifully. There is more luminescence in environment channel than the luminance channel if you can believe that! Only one problem now. When I want to rotate the object in animation of course the environment stays where it is as it should. Is there any way to cheat that? Somehow I want the image to animate a slow roll on the dome surface?