Caustic

http://www.truecg.com/index.php?option=com_content&task=view&id=42&Itemid=29

A good tutorial resource, from Maya to Blender. this link is about how to render Caustic of glasses(refractions) in maya. simple and direct.

http://www.interstation3d.com/maya/tutorials/mray_caustics/caustics_example0203.htm

another more detailed site about doing Caustic of ocean, reflective object