If you’ve ever cursed the gods while trying to obtain good and reasonably cheap caustics in Vray, then rejoice. You will breath a sigh of relief as you go through this video tutorial, found on 3D Total. In it, Ricardo Eloy explains what at first seemed to me like a highly implausible trick to obtain the unobtainable: Crisp, complex and clean caustics in Vray, literally in seconds and using the default quality settings. But it works. It essentially hinges on the curious fact that standard Max lights that have been set to exclude all objects in the scene continue to generate caustic photons, even as they do absolutely nothing else. Although the method has some limitations, it gives you what used to be a very expensive output in Vray basically for free, and as such, it is a tip worth a large multiple of its weight in gold.
Below for some context two images, the first calculated in Vray using the said method (the caustic photon map took, without kidding, seconds to calculate) and the second in Maxwell, which, as you will know, gives you free, physically accurate caustics out of the box (whether you want them or not) at the expense of rather long render times. So which do you prefer?