Hi, I don't have time to trouble shoot this one today but there are two things to try: 1) Increase the Caustics filter size. It increases the fidelity of the caustics. I suspect that the lower/default caustic setting is allowing the jitter. This will increase render time though. 2) For the cube shapes, you're really not gaining anything by using caustics because of the flat sides - a curved shape would be different. Simply selecting light through transparency should be ok. If you want a caustic look, you can also create a gel for a light within the cubes. You can get all of the look with none of the speed penalty on render. Mark