PanoTools:
Re: entrance pupil - nodal point
Erik Krause 2004-Nov-09 21:35:10
On 9 Nov 2004 at 18:42, Milko Amorth wrote:
> 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.
Not exactly true. In optical terms a 'virtual image' is f.e. what you
see if you are looking through a magnifying glass (which is exactly
what happens if you look into a lens where the front lens group forms
a convex lens). In this case, the virtual image is always further
away from the you than the object (thats why you see it larger). In
almost all cases this is not the 'no parallaxe point'. If you say the
entrance pupil is the diameter of the virtual image of the aperture,
you're exactly right.
[...]
> 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.
These two should be identical, at least for lenses where the focal
length doesn't change with viewing angle (as is the case for fisheyes
f.e.). In german the plane (rectangular to the optical axis) from
which the nodal point is the middle is reffered to as "vordere
Hauptebene". It is the (virtual) place of an ideal lens where the
lens equation and other geometry aspects like f.e. depth of field
refer to. In an ideal lens light rays that pass through this point
are not refracted in any way. That's why you can rotate around this
point without parallaxe.
The german translation of 'entrance pupil' "Eintrittspupille" stands
for the diameter of the effective aperture of the lens. In a
refraction diagram it is located on the "Hauptebene". I found no
translation for "Hauptebene" in english, so may be it is called
'entrance pupil' there...
Bit complicated to explain in english because I know all the optical
terms in german only...
best regards
--
Erik Krause
Ressources, not only for panorama creation:
http://www.erik-krause.de/
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