meters the diffusion circles become 0.034, 0.030, and 0.017 mm for the 
diaphragms 5.6, 6.3, and 11 respectively. The negative material was dia- 
positive plates of low sensitivity and panchromatic aerial photography 
film of high sensitivity. The resolving power tests were made for collec- 
ting experience for comparisons between the actual different emulsions, 
filters and cameras only. 
For the determination of the resolving power a microscope was used. 
The last figure in the test target where the lines still were clearly visible 
was used as a measure of the resolving power. The same results were 
in general obtained when the estimations were made by different obser- 
vers. 
When the conditions of the photography were identical for differ- 
ent cameras a comparison between the resolving power of the cameras 
could be done directly. In Diagrams 17—26 some results of the tests 
are demonstrated. The resolving power was determined as an average 
of the observations along the four half diagonals. 
4.3 Investigations of acrial cameras after oblique photography from 
the tower 
In a special test program oblique photographs were used. The main 
purpose of this program was to collect experience for later experiments 
with aerial cameras from higher towers where vertical photography of 
test fields cannot be arranged due to the construction of the tower, 
  
  
> X 
H 
Fig. 11. Cross section through the camera and bundle of rays during oblique 
photography. 
T" li 
4.31 The arrangement of the test field on the ground, the photography 
and basic measurements 
It is desired that the test points in the image form a regular square 
grid. The corresponding points on the ground must therefore be located 
44