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Mailinglist:PanoTools
Sender:Rik Littlefield
Date/Time:2004-Nov-11 17:35:30
Subject:Re: entrance pupil - nodal point

Thread:


PanoTools: Re: entrance pupil - nodal point Rik Littlefield 2004-Nov-11 17:35:30

--- In #removed#, Dan Slater <#removed#> wrote:
> Hopefully this will help clarify the entrance pupil / nodal point
> issues as related to stitched panoramic imaging:
> 
> 1. The center of perspective is the lens entrance pupil,
> which is the virtual image of the aperture stop when viewed
> from the front side of the lens.

Dan,

Can you clarify a couple of fine points for me?

1. I'm having trouble with the precise definitions here.  I'm getting 
that the entrance pupil -- the virtual image of the aperture stop -- 
is an outline enclosing an area, but the center of perspective is a 
dimensionless point.  Apples and oranges, on the surface.

Is it more correct to say that the center of perspective is the 
intersection of the lens axis and the plane containing the entrance 
pupil?

2. What happens in the case proposed by Erik Krause, where at full 
aperture the limiting stop is not the variable iris?  If the center 
of perspective is exactly tied to the image of the aperture stop, 
then it seems the center of perspective will suddenly shift from one 
place to another as the lens stops down.  Possible, I guess, but it 
does not seem likely.  

What I imagine will happen is that the center of perspective will 
stay at the same place.  I also imagine that place will be very near 
the image of the iris, but perhaps *slightly* displaced from it 
depending on the exact placement of the iris.  (I think it cannot be 
displaced very much, or the lens would vignette when stopped down.)

--Rik





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