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Where protection is furnished for the camera, the basic factors 
to be taken into consideration for the lens are the environ- 
mental conditions prevailing in the cabin. The glass cover plate, 
however, creates a certain amount of changes, too. The plate 
does in fact give slightly under the pressure exerted upon it 
from inside. On top of this the refractive index of the cabin 
atmosphere is not the same as that of the external atmosphere 
- this again on account of the pressure differential. To obtain 
an overall picture of the effects produced, those of the lens 
and those of the cover plate must be taken together. 
If no protective glass cover plate is provided to shield the 
lens, it is from the lens alone that all the effects stem, in 
accordance, that is, with the environmental conditions defined 
under 2.2. 
Ihe reader is expressly reminded that the objective of our 
investigation is to examine the optical changes produced by 
environmental conditions in and immediately in front of the 
aerial survey camera, Thus the refractive effect of the inhomo- 
genous atmosphere between the earth's surface and the camera is 
ignored for the purposes of our Study. This and other influences 
(e. g. the earth's curvature) are nevertheless dealt with in 
relevant passages, e. g. /1/. 
Calculations were performed for the following aerial photography 
lenses which are available as standard components for ZEISS 
aerial survey cameras: 
  
  
  
  
  
  
  
focal format angle 
length 2 of 
mm cm view 
super-wide angle: S-Pleogon A 4/85 85 23 x 23 125° 
wide-angle: Pleogon A 4/153 153 23x 23 939 
intermediate-angle:Toparon A 5.6/210| 210 25 x 25 759 
0 
normal-angle: Topar A 5.6/305 305 23 x 23 56 
  
- table 2 - 
0 0