I just started into yafray, and here is my latest render, where i FINALLY got transparancy and caustics right. 
interesting, could we get a 640x640 render to make critiqueing(sp) easier?
Thereās what appears to be artifacts around the edges.
Oh well, at least itās not like the images I make now which even @ndy said is CRAP.
I like it, though I might suggest trying photon lights from multiple angles to make it look much better, it looks good, but I honestly donāt see many caustics. Maybe you could pull the camera back some so we can see it better.
Kansas, remember what happened last time you went along this path. Prove him wrong.
Actually, I can see the caustics on the inner floor of the sphere. I think you could fix the artifacting on the edges by using āset smoothā on the sphere, but that may reduce the caustics.
Nice job. Iām pretty sure the the āartifactsā around the edge are not artifacts, but dark faces of the sphere where light is being refracted away from the camera. turning set smooth would get rid of it, but since itās rendered wtih sharp faces it appears as it should.
the āartifactsā were done on purposeā¦ using an icosphere. Having just a sphere with the position of the lamps would be too plainā¦