PanoTools:
Re: entrance pupil - nodal point
Dave 360texas.com 2004-Nov-12 19:19:59
As I have followed this discussion with great interest from the
beginning I offer these two pictures.
Image 1. I borrowed and modified the your lens picture so that I
could display it here. This is the way we have our equipment
arranged. Notice that the fisheye lens is center point in the drawn
optic glass.. at which point the image is inverted. We do rotate
about this point and get good stitching results.
Image 2. The next picture is of a fisheye with no iris or aperature
with groups of optics which channel the incoming light rays. It
appears that the image is inverted about mid center of the lens.
I suspect that the point where the image is inverted is a nodal
point.
Image 1 http://360texas.com/images/nodalpt.jpg
Image 2 http://360texas.com/images/fe.jpg
/s/
dave @360texas.com
--- In #removed#, "Erik Krause" <#removed#>
wrote:
> On 12 Nov 2004 at 14:21, John Houghton wrote:
>
> > > What you show here is the example of a pinhole camera. If you
follow
> > > the light rays further to the right, you would see that there
is only
> > > one rotational position of the lens, where A and B are
together on
> > > the film - the position where A, B and N1 are on the same
straight
> > > line. Such a narrow aperture in front of the lens simply
limits the
> > > field of view...
> >
> > Erik, Of course there is only one position where A and B are in
line
> > when you rotate about the nodal point. This is why it is the
wrong
> > point to choose for the no parallax point. The example is no
more a
> > pinhole camera than any lens stopped down to f/16. The light
rays
> > get refracted by the glass just the same. The aperture
certainly
> > limits the field of view, but I still get a full image with such
an
> > aperture in front of a 50mm lens on my D60.
>
> You're right with your experiment, since you get a projection of
the
> hole in front of your lens as a circle of confusion (as is the
case
> for any aperture). But see what happens if you focus to the
> previously out of focus object - The objects move away from each
> other...
>
> It makes a difference whether the aperture is inside the physical
> lens or outside. If it is inside you must calulate with it's
> projection (what is called 'virtual image' by dan) not with the
> actual physical location.
>
> best regards
> --
> Erik Krause
> Ressources, not only for panorama creation:
> http://www.erik-krause.de/
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