i 
dr = 
r 
8.2.2 
dc 
c 
which can be regarded as the first term in an expression for radial distortion 
dr = a\r + a 3 r 3 + a 5 r 5 8.2.3 
Thus we obtain 
dc 
dr = — r + a 3 r 3 + <z 5 r 5 . 8.2.4 
c 
Here we use this technique to give all determinations the same camera con 
stant, 256.000 mm. It is now possible to compare the different radial distortions, 
but when we want to test the significance of the differences between them we 
have to propagate the error of the camera constant to the radial distortion. 
The results of the computations are shown in Figs 13 and 14. When the radial 
Fig. 13. 
Stereo-Medical-Nikkor, camera 1. Upper curve: radial distortion, dr, with a 95 °/o confidence 
interval. Lower curve: the radial part of the residual vector. From left to right the f-stop 
values are 45, 45, and 11. 
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