I put an image "Sea Patrol :: just checking" in the gallery, and I was criticized for lack of underwater effect. If that means that I didn't use a "caustic" to simulate the effect of refraction thru waves: in the course of over 300 scuba dives I haven't seen caustics on the bottom much. If (1) the bottom is shallow and so within the range of the focal lengths of the curves that the surface of the water assumes as the waves pass (multipled by the sine of the altitude angle of the sun), and (2) if the water is clear enough, and (3) the sun is not behind a cloud, then caustics are to be expected. But in low-visibility UK waters I am usually out of visibility range of the surface even in quite shallow water and the light from above is diffuse, and the weather is often cloudy. And in the Red Sea I was usually too deep for caustics to show, and anyway they are often hidden by the color patterns of the bottom.