PanoTools:
Re: entrance pupil - nodal point
sdubose99 2004-Nov-09 08:24:02
Manfred, guten tag... for all intents and purposes of producing a
panorama images with little parallax, nodal point and entrance pupil
are the same.
Scott
The following is from John Houghton in the UK:
Nodal point: When you have a lens made up of two or more elements,
the resulting combination of lenses will have an effective focal
length "f". On either side of the lens will be the two focal planes
where objects located at infinity will be focused. If you measure a
distance f back towards the lens from the focal planes, you will
arrive at the principal planes. In a simple lens, these will
conicide, but in a complex lens they will be separated. The points
where these principal planes cross the lens axis are called the
principal points. These points are also where the nodal points are
located. A light ray incident towards the front nodal point will
emerge as from the rear nodal point in a direction parallel to the
incident ray. In a camera, if the lens is rotated about the rear
nodal point, the image will remain stationary on the film located at
the focal plane. This is an important factor in the design of
panoramic cameras in which the lens rotates rather than the camera.
Entrance pupil: Somewhere between the elements of a complex lens
will be the iris. If you look through the front of a lens, you will
see a virtual image of the iris formed by the front elements and
this is called the entrance pupil. Likewise, there is an image of
the iris formed by the rear elements of the lens called the exit
pupil. All light rays passing through the lens pass through the
entrance and exit pupils. The front entrance pupil is therefore the
centre of perspective of the lens. Rotating the camera about this
point will avoid parallax errors.
In the context of stitching multiple image panoramas, all the
practical methods described for determining the position of the
nodal point in fact find the position of the entrance pupil, not the
nodal point. Since it is the entrance pupil that is required, then
the methods give the desired result.
--- In #removed#, "manfredgruber"
<#removed#> wrote:
>
>
> Hi,
>
> Can someone explain in easy words what`s the difference between
> lens entrance pupil (centre of perspective)
> and
> nodal point
> ? Or is there a good reference somewhere in the internet (i didn`t
> find)
>
>
> Regards
> Manfred
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