I discovered recently (purely by accident), that you can get some pretty convincing refractive caustics using just the Sky shader.

Previously, I was under the impression that they could only be achieved using an emissive shader. However, using a HDR map with some high dynamic areas like a window or sun can give you some impressive results.

Tutorials here: MtoA, C4DtoA.

Autodesk Japan have made available the models used in the movie below from WOW inc.

‘Max Man’ and ‘Maya Man’ are made available free of charge for use within the software applications.

Below are Arnold renders of each model.