EI
JOURS REN COS NET RARE
Z
ee 0 et
an nm M A dili Rr ete pt ce ER GM t ae d RENS OA Né el 2 DAMES
Fig.5 illustrates examples for the proposed image quality criteria
for some high-quality aerial survey lenses. Qj, Q2, Q.], Q-2 are
respectively the arithmetic, quadratic, harmonic and quadratic
harmonic means of the integrated MTF with respect to image field.
Curves 1,4,6 and 7 correspond to wide-angle lenses (2 w = 90°,
f = 150 mm ) of different manufacturers. In addition, normal and
super-wide angle lenses are presented. The ratios qj, qo for
different objectives vary as follows:
0.92<q1=0.5 ; 0.85 <qo < 0.25
Furthermore, objectives 5,6 and 7 are of newer designs having
vastly improved performance. The appropriate areas are not norma-
lized to the diffraction-limited MTF. A comparison of different
sets of quality curves; of which two are shown in fig.6, illu-
strates that the result of the evaluation of the image quality
criterion depends not too much on whether the area below the
MTF curves, limited by Rg, the spatial frequency, is chosen with
or without the area below the threshold curve but on the averaging
over the image field. It seems that for aerial survey lenses the
area below the MTF curves up to a limiting spatial frequency,
Rg, is adequate for practical comparisons. Typical curves in
fig.6 are 1 and 2, they are not normalized; subtracting the
threshold contrast curve leads of course to lower values but
the shape and the differences between the curves are almost
the same (17, 21): qj and q» remain practically unaltered.
With the proposed image quality criterion the influence of gela-
tine filters on the image quality was analysed for two different
objectives. Fig.7 illustrates the reduction of image quality as
a result of gelatine filters for two aerial survey lenses. The
new high quality lenses are developed to a point where gelatine
filters as well as environmental conditions reduce the image
quality considerably.
Images obtained for two different field angles of two objectives
are shown in fig.8, and the corresponding MTF curves in fig.9
along with the threshold curves for high and low object contrast
(1 resp. 0.23).
-
9
