Am 08.08.2016 um 09:32 schrieb pkrskr:

>> In a scenario with a diaphragm in a different plane than the lens, this
>> simplification does not hold, as we would have to place the virtual
>> aperture at different X/Y coordinates depending on the point P (compare
>> the diagram, in which the red ray -- which should be at the center of
>> the virtual aperture -- passes through the lens at an offset from the
>> camera axis).
> 
> This is the most interesting point. In your first explanation, you mentioned
> that the red ray is originally drawn through the center of the nominal camera
> location (which is the virtual aperture), and I thus presumed that the ray went
> through the pole of this virtual aperture (since we were tracing through a
> pinhole). However, now that you mention it, I see that the pinhole ray was
> traced through the center of the real aperture and thus happens to be shifted in
> X/Y on the plane of the virtual aperture and the jitter is applied across this
> shifted point. This is indeed different from the above scenario where the lens
> and the diaphragm are at the same plane.

No, that's a misunderstanding there. The pinhole ray is also traced
through the center of the /virtual/ aperture.

> However, could you clarify how the locations of the real aperture and the
> virtual aperture are decided? And does this mean that the nominal camera
> location is the position of the real aperture?

As I said before:

"(1) The nominal camera location always corresponds to the center of the
virtual aperture."

As a matter of fact, POV-Ray /never/ actually "thinks" of the real
camera geometry in the first place, since the geometry is only specified
indirectly. When you set up a camera in POV-Ray, you are essentially
specifying:

- The camera location = center of the virtual aperture.
- The direction of the camera axis (via `direction` or `look_at`).
- The distance between the virtual aperture and the plane in focus
(again via `direction` or `look_at`).
- The effective horizontal and vertical opening angle of the camera
(either via `up`/`right` and `direction`, or via `angle`).

There is an infinite number of physical cameras that satisfy any given
combination of these parameters.

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