534 Test targets 
For the investigation of aerial photographs it is naturally interesting to knoy 
the size of the smallest details on the ground that can be seen on the photograp} 
The resolving limit gives at least in part the answer to this question, By 
aii : : ; Ie 
quently it is no less interesting to be able to follow a certain contour of the d 
graph or to know the accuracy with which irregularities of this contour an | 
reproduced. For this purpose “contour targets" (fig. 12) have been teste 
The size of the smallest observable "hook" in the straight line on lh 
contour target has in this investigation been used as a measure of the “contoy 
resolution”. 
In addition two types of conventional test targets have been tested, viz, fy | 
line groups of Foucault type, where the length of line is 5 X the width of] 
and Howlett targets where the width of the ring equals the inside diame 
Three-line targets have been made in two low-contrast versions, the design i | 
the targets being based on certain measurements on different types of gromi 
with an exposure meter. In one case the density values are 0.05 for the line 
and 0.25 for the background, bright targets, whereas in the other case fh 
corresponding values are 0.70 and 0.90, dark targets. The same density valu 
have been used for the Howlett targets, which in addition were made in coloy | 
The ring of the colour targets is green, while the inner circle is dark brown ani 
the surface outside the ring light brown. It was primarily intended to reprodu 
the colours of woodland, as seen from the air. The contour targets were madei 
high contrast. 
The diameter of the largest annular figures is 225 cm whereas the great 
e. 
length of lines is 317 cm. The variation in size is V2. The total length of ll 
contour targets is 644 cm, the magnitude of the hook varying from à li 
35 em. 
  
  
  
Fig. 12. Contour test target 
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535 Aeria 
The test ta 
September an 
for aerial pho 
5) to 75 m/se 
from 1,000 m 
the test targe 
758 photogra 
A prelimin 
made in Dec: 
photographin; 
lit and put o 
High degre: 
values. À moi 
One single off 
checks have : 
596  Resul 
A graph of 
figure from tl 
The shape of 
for each type 
material. The 
distance of t| 
guidance fron 
by the lack o 
has been affe 
The results fi 
The effect o 
while the res 
different time 
Table 9. Var 
ee 
———— 
Lines dark ,. 
Lines bright 
Annuler dark 
Annular brigh 
Annular colou 
Contour high- 
— re 
  
1—561100