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POV-Ray can simulate focal depth-of-field by shooting a number of sample rays from jittered points within each pixel and averaging the results.
To turn on focal blur, you must specify the aperture keyword
followed by a float value which determines the depth of the sharpness zone.
Large apertures give a lot of blurring, while narrow apertures will give a
wide zone of sharpness.
Note: while this behaves as a real camera does, the values for aperture are purely arbitrary and are not related to f-stops.
You must also specify the blur_samples keyword followed by an
integer value specifying the maximum number of rays to use for each pixel.
More rays give a smoother appearance but is slower. By default no focal blur
is used, i. e. the default aperture is 0 and the default number of samples is
0.
The center of the zone of sharpness is specified by the
focal_point vector. Objects close to this point are in focus and those
farther from that point are more blurred. The default value is
focal_point<0,0,0>.
Although blur_samples specifies the maximum number of samples,
there is an adaptive mechanism that stops shooting rays when a certain degree
of confidence has been reached. At that point, shooting more rays would not
result in a significant change.
The confidence and
variance keywords are followed by float values to control the adaptive
function. The confidence value is used to determine when the
samples seem to be close enough to the correct color. The
variance value specifies an acceptable tolerance on the variance of
the samples taken so far. In other words, the process of shooting sample rays
is terminated when the estimated color value is very likely (as controlled by
the confidence probability) near the real color value.
Since the confidence is a probability its values can range from
0 to <1 (the default is 0.9, i. e. 90%). The value for the
variance should be in the range of the smallest displayable color
difference (the default is 1/128). If 1 is used POV-Ray will issue a warning
and then use the default instead.
Rendering with the default settings can result in quite grainy images. This can
be improved by using a lower variance. A value of 1/10000 gives a
fairly good result (with default confidence and blur_samples set to something
like 100) without being unacceptably slow.
Larger confidence values will lead to more samples, slower
traces and better images. The same holds for smaller variance
thresholds.
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