parallax between two different pictures

When reading tutorials about making nice panorama pictures you often find information about the nodal point and that the camera should be adjusted to rotate around it. In our first panorama tests we didn't care about, but this week-end we tried some pictures with objects in the foreground and had some problems with parallaxes.

In the picture at the right hand side you see two picture details taken from two picture we made with a rotation of 30 degrees. In the upper picture you can see a much larger part of the mast below the handrail than in the lower picture. The camera only had a distance of less than one meter to the handrail.

Camera location on the overhead crossing

So we tried to figure out what was the problem and how to fix it. First of all we found a very nice article Theory of the "No-Parallax" Point by Rik Littlefield which explains in detail what the "No-Parallax" Point is and why it is often mixed up with the nodal point. The correct expression for this point should be entrance pupil.

The next step was to find out how to measure the correct entrance pupil for our setup. We found a tutorial by Alain Hamblenne, but the problem is that the camera we use is to large to get it in the correct position. So our next steps will be to modify the motorized panorama head to be able to move the camera in the correct position.