100 mm 
The largest calibrated distortion values are near 
at the bounds of the image. In table 3, the 
differences of these largest values of the 
Calibration certificate from the estimated curves 
are reported. The difference in percentage is 25% 
at maximum value. Apart from the most exterior 
zones of the image, these differences are much 
lower in the remaining image area. In particular, 
one could think to make more than one grid 
calibration, at least three of them, and take the 
mean of the distortion curve to have a more 
accurate estimate. From one test to another the 
results are rather different. The largest difference 
from test! to test3 is even 40%. 
Table 3 - Comparison of the maximum 
distortion values 
CURVE 
ROLLEI 
TESTI 
TEST2 
TEST3 
drmax 
0.188 
0.219 
0.190 
0.141 
Diff. 
+0.031 
+0.002 
-0.047 
Diff.% 
16% 
0% 
-25% 
R 
Fig. 10- Radial distortion curves for 35 mm Minolta amateur 
camera zoom lens 
5. THE MINOLTA ZOOM LENS 
An amateur camera SRC 35mm Minolta 
equipped with a zoom lens 35mm-210mm 
has been tested. The radial distortion curves 
have been determined at the focal distances 
of 35mm, 50mm, 100mm, 210mm. As plate 
reference system the negative frame was 
taken. The graphs are shown in fig. 10. It is 
noticeable that from 35 to 210 mm the 
distortion changes from cushion type to 
barrel type. The least distortion takes place 
at a distance of 50mm, probably the focal 
length taken as reference for the design of 
dR 
50 mm 
rlîrTthN^L 
R 
Fig. 11 Zoom Minolta lens. 3D distorsion model from top to 
bottom 35mm, 100mm and 210mm