ERNEST EEE EEE 
Tren 
TTT RST 
  
TRE 
(670) 
By the aid of slides, I demonstrated how long distance photographs are 
diffused, due to the fact that the sunlight which the object reflects is bent to a 
greater or lesser degree, by solid, liquid or gaseous particles which exist in the 
air. It is then advantageous to use panchromatic emulsions very sensitive to red 
orinfrared-sensitive neg- 
ative material, together 
with suitable color fil- 
ters, as the rays travel 
with less interruption 
the longer the wave 
length used. A wood, 
which cannot be pene- 
trated on account of 
blue haze, appears in 
such a negative exposed 
by long-wave radiation 
as very detailed terrain 
with individual trees 
and bushes standing out. 
= Je : : In like manner, the de- 
Fig. 2. Thanks to the use of infrared-sensitive negative material : : 
the diffusing effect of the distance is eliminated. The distance tails of a ship Are re- 
to the lighthouse and the ships is about 20 miles. The stones of produced with absolute 
the reef in the middle distance appear to be close to the camera, clarity in spite of the 
but in reality are nearly 15 miles away. Photo: R. Thorén. diffusing effect of the 
(Enlarged photo detail). distance haze. Details, 
diffused in the panchro- 
matic pictures, stood out sharp and clear in the infrared ones, also at very large 
distances, as for example in the picture of Fig. 2, 20 miles. Objects in the middle 
distance of about 15 miles were registered perfectly clearly as if they had been 
close to the camera. The focal length used was 118” (300 cm). The emulsion 
was an Agfa product type Infrared 700 and the filter a dark red one, Zeiss 
type H. 
It is, however, not only distance haze but also turbulence in the air which 
causes a diffusing effect in the pictures in long distance photography. Especial- 
ly in cameras with strong optics this trouble may spoil the photos totally or 
partially. The quality of the picture, however, is improved essentially, if the 
aperture of the camera is decreased. As an illustration I showed pictures taken 
under similar atmospheric conditions, with two cameras having the same focal 
length but different apertures, f :6 and f : 25 respectively. In the first case, the 
details of the picture were spoiled by thc turbulence in the air, while in the sec- 
ond case with the camera with the small aperture, the details of the object were 
registered with excellent sharpness, see Figure 3. For that long distance shot I 
used a German built lens camera with a focal length of 118^ (300 cm), Agfa 
Aeropan and Zeiss’ red filter type F. The distance to the object there, an escort 
destroyer, was 19 miles. Main deck is below horizon but forecastle, bridge, 
stacks, masts, guns and Ack-Ack are well visible in spite of the considerable 
distance. The vessel was patroling a narrow channel in an important minefield, 
and I for my part was engaged in mapping the same field, its boundaries and 
channels, by plotting and distance measuring in ground reconnaissance photos. 
  
      
     
    
    
  
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