This could be caused by the could age. As the Pyrocluster is based on particles, this age function could be fitted in a situation with a constant emitter. My scene create cloud with an irregular surface and the particles are just matrix without birthing and life. So there are no supplemental particles to keep the cloud displaying. To deal with this, I have to render again without cloud age. It might sacrifice some rolling effect, however the whole feeling of this shot would not be damaged.
Another thing is my showreel has began to be made. I want to begin with my previous work like this guitar player robot. Owing to my purpose to make it move, it can not be rendered by Keyshot. Consequently I attempt to use Mental Ray of 3ds Max to render.
In order to have better result, I watched Aaron F. Ross' tutorials to understand the renderer better. One thing really inconvenient is there is some annoying gains when rendering with depth of field using Mental Ray. It could only be removed a little bit when increasing bucket. But that movement will loose some detail and make the image murky. Hence I decided to render out rpf files with z-depth so that I can add some depth of field in After Effects. It could not be best solution, but considering the time arranging and the visual quality, this is a rational plan.

















