Tim Attwood wrote:
> The origin of a ray is perturbed semi-randomly X,Y along the "film",
> from there it passes through the focal point until it has some
> color from raytracing the scene. Aperture controls the amount of
> random displacement of the origin of the ray. Each final pixel on
> the "film" is the weighted average of the sample rays cast. At certain
> sample sizes the displacement pattern is pre-set to provide a good
> hexagonal grid, as more samples are used they are added randomly
> positioned in addition to the pre-set grids. So for example if you
> have 50 samples, 37 of the samples will be the largest pre-set
> pattern, and 13 samples will be random patterned. In general the
> pre-set patterns are weighted so that rays that are displaced farther
> from the actual pixel origin have less contribution to the final pixel
> value. That's why it's considered arbitrary, the falloff data comes
> from an array instead of a function.
> Overall it's close to being recpirocal of displacement distance.
> 
> Unfortunately this means that there is no easy way to set DoF without
> accounting for differences based on samples, and general POV scales.
> 
> The results are also not diminished in luminance over distance
> like with a RL camera, so far away blurred objects can look brighter.

Very interesting.  Do you know what these "certain" sample sizes are? 
Is there any benefit (performance or otherwise) to using certain 
blur_samples values?  (I'm thinking of how there are certain "optimal" 
values for adaptive area light sizes.)

-- 
-The Mildly Infamous Blue Herring

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