The scene below results odd and disturbing black artifacts (black 
pixels) in blurred areas. The reason is too high variance: 1e-5 is not 
small enough. One can get rid of these artifacts by setting variance to 
0. This happensi in most scenes and basically means that in order to 
have good looking FB one has to use variance 0 allways.

The question is: what causes POV-Ray not to react when trying to set a 
lower variance than 1e-5 that is still >0?  If I write 1e-6, for 
example, the resulting image will be identical. Is this a bug or a 
feature? And is it caused by focal blur calculations, parsing the float 
or simply lack of precision in 64-bit floats - or something totally 
different?

*Testing more*

Oddly, when I set variance 2.0133175e-322 or smaller, the artifacts 
disappear. I didn't want to iterate more digits :)

PS. Version 3.5 on Windows.

Regards,
Severi Salminen

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camera{
     location <3,3,-5>
     look_at <0,0,0>
     aperture 30
     blur_samples 100
     variance 1e-5
     focal_point <0,0,0>
}

plane{y,0
     pigment {checker rgb 1 rgb 0}
     finish {ambient 1}
}

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