Am 09.11.2016 um 05:28 schrieb Mike Horvath:
> http://wiki.povray.org/content/Reference:Camera#Focal_Blur
> 
> The docs say, "The center of the zone of sharpness is specified by the
> focal_point vector. The zone of sharpness is a plane through the
> focal_point and is parallel to the camera. Objects close to this plane
> of focus are in focus and those farther from that plane are more
> blurred. The default value is focal_point<0,0,0>."
> 
> How can a plane be parallel to the camera? Can't a plane only be
> perpendicular to a vector?

Interpret it as "parallel to the image plane" -- or, in other words,
"perpendicular to the camera axis".

> Also, I don't understand why a plane is used at all. All points
> equidistant from focal_point should form a sphere, don't they?

Uh, yes, technically, all points equidistant from _any_ given point form
a sphere, but how would a sphere centered around focal_point (= an
arbitrary point by which the location of the zone of sharpness is
defined) be of any relevance?

Presuming that you mean "all points equidistant from the camera
location", the answer is: Yes, that would also be a sphere -- but the
zone of sharpness in a normal camera is _not_ the set of points
equidistant to the camera lens; rather, in a real-life camera it is the
set of points equidistant to the image plane, and that's also the case
for POV-Ray's camera.

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