PanoTools:
Re: Re: entrance pupil - nodal point
Milko Amorth 2004-Nov-09 18:42:30
Hi Manfred,
This is the wisdom (By Joseph S. Wisniewsky) I have been living by until
now:
Entrance pupil - The "center of perspective" of the lens. It is the center
of rotation for panoramic photography. Panoramic photographers sometimes
refer to it as the "nodal point", but it's not. This point is the virtual
image of the len's aperture.
Exit pupil - The point where light radiates from the lens to the film or
sensor. Useful of you're doing macro photography with a reversed lens.
This point is the virtual image of the len's aperture, as seen from the
back of the lens. This point also tells you how well the lens will work on
a digital SLR. If it's close to the sensor (50mm or so) you may see
vignetting even on an "APS sized" DSLR. It it's over 90mm, you won't see
vignetting, even on a full frame DSLR.
Front nodal point - The virtual location of the lens, from the object.
Used for calculating macro ratios and "effective" f stops in macro
photography. This point is not used for panoramic photography, use the
"entrance pupil" instead.
Rear nodal point - The virtual location of the lens, from the image side.
Used for calculating macro ratios and "effective" f stops in macro
photography.
This is, at least for me, the online bible to the panographers nodal point:
http://michel.thoby.free.fr/
Have a great day and fun learning new things.
Cheers und mit freundlichen Gruessen,
Milko
On Tue, 09 Nov 2004 09:24:21 -0000, manfredgruber
<#removed#> wrote:
>
>
> Thx for the attached description.
> For me, it`s not clear at all. But if all the measurement for "nodal
> point" and "entrance pupil" to avoid parallax error means the same at
> the end, it is ok for me.
> Is there a picture that could describe it for a visual thinking like
> me?
>
> I tried to translate it to german is it correct?
> entrance pupil -> Eintrittsblende
> nodal point -> Kontenpunkt, optisches Zentrum einer Linse
>
>
> Regards
> Manfred
>
>
> --- In #removed#, "sdubose99" <#removed#> wrote:
>>
>> 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
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
--
Milko Amorth
360image.de
VRCanada.ca
Interactive Imaging for your Digital World
fon++49.711.3655318
fax++49.711.3513896
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