Am 04.08.2016 um 18:23 schrieb udyank:
>> At the same time, the direction of the
>> rays is adjusted in the opposite direction, so that each ray still
>> passes through the same point on the plane of sharpness that it would
>> have passed through without the jittering.
> 
> Are you saying that we presume there is a finite-aperture lens in the middle b/w
> the camera plane and the scene, which bends the rays? Supposing there is a lens
> in the middle, the rays from the camera bend through the lens and go to the
> scene at some point P, does the "adjustment" mean that all jittered rays will
> also go through P or points scattered around P (as per the jitter on the other
> side) ?

I'm not sure if we're saying the same.

Note that in a somewhat idealized lens camera, all light rays from (or
passing through) an arbitrary point P on the plane of sharpness meet at
a specific point P' on the image plane, but they might pass through any
other arbitrary plane through different points Q_i.

POV-Ray picks such an arbitrary plane parallel to the image plane (and
also parallel to the plane of sharpness), and jitters the point Q_i,
while keeping constant both P' (which is trivial because it's the pixel
currently being rendered) and P (which requires some math but isn't too
difficult).

Where that arbitrary plane is located doesn't really matter; it could
indeed be the plane of the lens. However, it makes sense to instead
pretend that it's the plane of the diaphragm, since it's the size of the
diaphragm that corresponds to the jitter radius.

The only conceptual problem there is that the diaphragm is usually
somewhere between the physical lenses within the lens assembly, so
instead of the physical diaphragm the truly relevant entity is the
"virtual diaphragm", i.e. the diaphragm as and where it appears to be
when seen through the front of the lens assembly.

>> To compare this with a real camera lens, the camera location can be
>> thought of as the center of the diaphragm (or, more precisely, the
>> diaphragm's virtual image as seem through the lens), and the jittering
>> of the rays accounts for the fact that the diaphragm's aperture is not
>> infinitesimally small.
> 
> I didn't really get this part. How would jittering account for the aperture
> size? Would it be possible for you to explain this with the help of an image?
> It would be really helpful.

I'll try to throw together something.

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