o.k., thanks, mark. i was using one spot and one bulb, which gave bad shadows, so I killed the bulb, which wasn't present in the default carrara caustics scene. scene background/backdrop also made it look wacky, so I killed that. it worked better with the default ambient than with no ambient. had caustics at 100, but found varying photon count and filter size (whatever that is) didn't affect the caustics much. the gems in my case were all pretty big, ranging from 2 inches to 5 inches, which of course is absurd, but all of 'em did reflected caustics, actually better than in yer example, but it seemed as if only the emerald refr. index did refracted caustics, which were poor compared to antoine's example above. I also jacked up reflection/refraction raytracing to 8 or 16, but it didn't help much, except to slow down rendering.