A Ba ER THA ERE 
then are cemented together. 
As the sensitivity of the film itself puts the upper limit, 
we have here an ideal combination for photography for forestry 
purposes within the green spectral range. In that case we obtain- 
ed essentially better photographic results. 
At photography for forestry purposes in the infrared the 
film (Kodak Aerographic Infrared Film) has the sensitivity curve 
Seen in fig. 7. It refers to sunlight. As can be seen the sensi- 
tivity is especially high within the higher wavelength range 7800 
to 8700 À with a sensitivity tail towards shorter wavelengths 
down to about 6700 À. At the Royal Institute of Technology we ma- 
nufactured in 1950 a provisory filter with the limit downwards at 
about 7500 A, This filter was used at the earlier infrared trials 
but was soon damaged as we did not have time to let it dry suf- 
ficiently after the cementing of the filter. 
Lately I have been informed that the Geographical Survey 
Office at the delivery of a new camera obtained a filter, made 
by the camera manufacturer, which has its lower limit at 7000 A. 
This I consider as being too low, even if the unfavourable effect 
will not become too disastrous, as the remission power of the 
leaves rapidly decreases strongly at the border of the visual 
range. It would be advisable, however, to manufacture a rather 
narrow infrared filter for photography for forestry purposes in 
the infrared range. 
Stockholm, Photographic Department, 
Royal Institute of Technology, 
July 1956. 
  
   
  
  
   
    
  
  
  
  
   
   
   
   
    
   
  
  
20% 
fe 
reflectonce ppercent) 
10 
  
Sensivity 
  
4C