Am 06.08.2016 um 13:25 schrieb pkrskr:

> I hope you can help with another small clarification. You mentioned to udyank
> previously that the virtual aperture plane could indeed be anywhere and could
> also thus be at the plane of the lens. But in your illustration, isn't there a
> change in direction of the ray between say Q1' and P1 because of the presence of
> the lens in between? Wouldn't it be incorrect to assume a ray straight from Q1'
> to P' without tracing the deviation caused due to refraction?

No, there is no such deviation through refraction.

First of all, it may be necessary to clarify a potential cause for
misunderstanding: POV-Ray does /not/ actually simulate a lens at the
position shown in the diagram.

Instead, POV-Ray uses the "virtual aperture" as the ray origin
/specifically/ to /avoid/ having to simulate the lens. The whole idea of
the virtual aperture is that (to the extent required by POV-Ray) it
gives the same results /without/ the lens as the true aperture does
/with/ the lens.


> If we were to assume that the virtual aperture was actually at the location of
> the (thin-)lens , then does this jittering exactly correspond to simulating a
> thin-lens by tracing multiple points on the lens and shooting rays towards P' on
> the object side and towards P on the image side?

I'm not sure I understand exactly what you are asking.

In a simple camera with no diaphragm, in which the lens opening also
constitutes the effective aperture, the aperture plane does indeed
coincide with the lens.

Consequently, in such a scenario, jittering of the ray origin does
indeed occur at the lens plane, and across the entire lens opening.

(Shooting rays toward P on the image side is not necessary, as P' is
computed from P using a quite simple formula, and there are no
intervening objects between the aperture and the image plane.)


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).

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