HowTo:Manual focal blur
From a discussion on the newsgroups:
"I render the scene multiple times (often 200, 400 or more times), but each pass has a very simplified, but at the same time completely randomised, set of paramters. When all those renders are summed together into one image, the random elements all combine to give a final scene that looks like one with a much more complex set of parameters.
Critically, when there are multiple "features" that all usually interact to push render times sky-high, I try to construct a scene that has the interaction as low as possible, and can render a few hundred images very quickly (each pass taking anything from 10 seconds to maybe a minute or two).
On multi-core machines I simply fire off as many POV processes as I have CPUs (or is that ALUs?).
I really must post a set of examples of each kind of effect that created with the technique, and then some examples of combining them all together.
A really really old example of multiple area lights, blurred floor reflection, anti-aliasing, focal blur and blurred refraction all done with stochastic rendering: