the origin, i.e. ry:ry e1:e9. With the definition abovementioned 
such a shape of the curve will correspond to the "theoretical 0-position”. 
As a curious fact, the Topogon lens satisfies these requirements very 
closely (at forward overlap of 60 %) as the nomograms of the vertical 
parallaxes show. That means that the instrument operator using pictures 
taken by means of this camera will approach the "theoretical 0-position” 
without being aware of it. 
Concerning these reflections a study of a lens distortion curve, 
imagined as a theoretical rectilinear, will give certain interesting conclu- 
sions in this respect, too. 
Due to the vertical parallaxes caused by the lens. distortion, super- 
imposed by the parallaxes of the tilt e, the displacement in the plane 
(x, y) of any point can be examined. However, such a study is not the 
subject of this paper. 
38 Conclusions 
As a conclusion it may be said that only the parallaxes of the original 
position of the two stereoscopic pictures, here called the "theoretical 0- 
position", correspond to the lens distortion curve. 
Thus it must evidently be established that, basically, any relative 
orientation of a pair of stereoscopic pictures will represent a "disturbed 
O-position". Therefore, it must be considered as impossible to derive the 
lens distortion curve from the residual vertical parallaxes. These paral- 
laxes have a very problematical relation, if any, to the lens distortion 
curve.