ac yy 2 LUE ST Se NAN aS TARO SPY Manual en patte civi AMA in of CE apo PR A E C a at Os potes ded 
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2:b.. Changes in Focus 
Changes in focus should not be mixed up with the changes in 
calibrated focal length mentioned before. With allowance being 
made for the focussing distance, the aerial survey camera as a 
fixed-focus camera is adjusted in the laboratory in such a way 
that the film plane lies in the plane of best possible image 
quality during exposure. Changes in focus are variations of this 
adjustment in the optical axis. They mainly result from the re- 
duction of air pressure with increasing flight height and only 
to a smaller degree from changes in temperature, The total 
influence is as follows: 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Installed in Exposed to atmosphere 
pressurized 
cabin 
with cover glass without cover glass 
cover glass @ 720mm lens temp. 9 lens temp. 
cover glass thickn. constant +7 C | dependent on 
45mm ext. temp. 
flight height |pressurized acc.2km | 6 km 14 km |6 km | 14km 
S-Pleogon A4/85 -0,03 -0,04 -0,07 | -0,01 | -0,05 
Pleogon Ah/153 -0,04 -0,07 | -0,15 | -0,0^ | -0,09 
Toparon A5,6/ -0,05 -0,10 | -0,17 |-0,08 | -0,1^ 
210 
Topar A5,6/505 -0,07 -0,15 0,25 («0,13 40,23 
- table 5 
Changes in Focus (in mm) - 
The list clearly demonstrates that changes in focus reach amounts 
which can not always remain neglected. The tolerable limit 
depends upon the aperture cf the lens. Under practical flight 
conditions O.0^ to 0.06 mm could be accepted for those with f/4, 
and about 0.06 to 0.09 mm for those with f/5.6.