Here is one using a ball as a lens by flattening the ball to 40%. This is using only the refraction node and set to 1.000. All other material settings are either black or 0.0000 I tried giving the lens a greenish tint by putting some color in the Refraction color, but I am getting some sort of interferance pattern. I suppose I could play around with it some more, but I should call it a night.