PanoTools:
Re: entrance pupil - nodal point
Erik Krause 2004-Nov-10 22:27:28
On 10 Nov 2004 at 8:59, John Houghton wrote:
> If you move the entrance pupil, by putting a small aperture a short
> distance in front of the lens, it is clear that this becomes the
> centre of perspective.
Sorry, but from optical geometry this can not be true. You don't
change refraction by putting an aperture somewhere, hence you can not
modify the location of nodal point with this technique.
You increase depth of field if you put an aperture somewhere in the
light path and you most likely introduce some vignetting (edge light
fall off) and limit the usable field of view, but the light rays pass
through the lens exactly the same way as they did without your
additional aperture.
> If you use the usual techniques for
> determining "the nodal point", then it is the position of the
> aperture that is found, NOT the nodal point, which hasn't changed.
Take a standard fisheye. The nodal point is somewhere inside the
front lens (if it was not'it couldn't cover 180°). The aperture is
far behind that point, as you can see in any lens diagram.
best regards
--
Erik Krause
Ressources, not only for panorama creation:
http://www.erik-krause.de/
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