Working on an university project I have run into trouble with mental ray. While I am fairly experienced in it, I have very little experience with GI and Caustics, especially in exterior scenes. So lets get to the problems.
This is my render as it is rendered by mental ray:
Scene is lit by a daylight system with mr Sun and mr Sky. Around 5M caustic photons and 2M GI photons. I am using a photon target for the sun with a diameter of 1500 cm.
As you can see there are a number of stray photons ending up on some surfaces makes small bright blue dots or cirkels. Also in the underwater area not lit by the sun, the photon solution is very very crude to say the least. I have already noticed these problems relate to the MR sky, or Mr physical sky environment as turning these off solves the problem (But obviously creates other problems).
So my first question is if anybody knows the reason why these stray photons appear? They seem quite random and appear in unexpected locations.
My second problem is the number of photons. I have been trying to see if the problems are the result of to few photons, but mental ray refuses to render if I increase photon numbers, both when calculating the photons at render time as with precalculating the photons to a photonmap. Mental ray will start calculating photons but simply stops around 4% in, caustics are completely absent in the following renders.
My second question is therefor if there is some sort of photon limit, or some known problem or reason why I cannot increase photon nummbers.