The Relativistic Black Hole Shader is a plug-in for Maya. The plug-in allows you to render gravitational lens effects caused by black holes in 3D. The shader uses a fast geometrical approximation. The implemented method is exact for weak fields of gravitation (Schwarzschild metric). The nearer you are at the black hole the less accurate the result will be. But you can achieve very nice results.
The shader must be used on a sphere object (nurbs, polygons or subdivs). In the picture on the left side you can see a scene without distortion. The grey transparent circle is a nurbs sphere. The picture on the right shows the scene after applying the black hole shader on the nurbs sphere. Note, that the red sphere now appears twice in the picture. It even can happen, that you see an object more often and from different sides at the same time.