I made a quick animation to test my Houdini–>AE script, and noticed something weird in the particle bokeh. It's very clear around 6 seconds into this, when the particles start to get near the camera:

https://vimeo.com/227242596 [vimeo.com]

The particles have a weird—almost rose-petal-like—bokeh look. I've created a super-simple scene to illustrate the weirdness: just a particle emitter and a camera. When rendered with depth of field and motion blur, the bokeh seems to converge towards a peculiar pattern. Can anyone tell me what's going on? (might need to zoom in on it a bit)



I realise I'm asking a lot of Mantra - the particles are very small (0.02), hence the high Pixel Samples. But it's almost like something isn't being jittered that ought to be.

Any thoughts?

(my wife says I've always had a strange bouquet but I think she means something different)