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