PanoTools:
Re: entrance pupil - nodal point
Rik Littlefield 2004-Nov-12 03:19:01
--- In #removed#, "Erik Krause" <#removed#>
wrote:
> On 11 Nov 2004 at 16:35, Rik Littlefield wrote:
> > Is it more correct to say that the center of perspective
> > is the intersection of the lens axis and the plane containing
> > the entrance pupil?
>
> Yes, for a rectilinear lens this is absolutely true.
> For a fisheye it is not, since the focal length (and hence
> all the optical geometry) depend on the viewing angle.
> If your fisheye has 8mm focal length, this is only true
> for the center. The focal length gets smaller to the edges
> and is virtually zero at the very edge of the image circle.
> Otherwise it would not cover 180° field of view (or more).
But for a fisheye, the plane containing the entrance pupil moves
forward if you view from off-axis. All I am saying is that the
center of perspective (the no-parallax point) for an off-axis angle
still corresponds to the plane of the entrance pupil, in its new
position closer to the front of the lens as seen from that angle. I
do not see where a change in effective focal length challenges this
interpretation.
--Rik
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