16 
-10 
LOG CT 
-20 
LOG M 
-20 
THE PHOTOGRAPHIC IMAGE, BROCK 
  
Ts es 
  
  
  
© 
HIGH-SPEED PAN AERIAL 
  
  
© 
SLOW DOCUMENT- COPYING 
  
  
  
  
  
  
1.0 2.0 
LOG (LINES/mm) 
Fig. 11. CT curves for two emulsions. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
1.0 20 
LOG R (LINES/mm) 
extremely high reso- 
lution. These curves 
show that focus set- 
ting depends to some 
extent on the kind of 
detail being  photo- 
graphed and the emul- 
sion in use. There are 
lenses which show this 
crossover effect to a 
greater degree and at 
lower frequencies, so 
that even on Super 
XX at low contrast 
the focus is not al- 
ways unique. 
Given the neces- 
sary data, these ex- 
amples could be mul- 
tiplied, but enough has 
been said to show that 
the phenomena of pho- 
tographic resolving 
power can be given a 
reasonable  explana- 
tion in terms of the 
frequency response of 
the components of the 
system. It will also be 
clear that there may 
be considerable reduc- 
tions in modulation at 
frequencies well below 
the resolution limit, 
and that there is no 
unique relation  be- 
tween the high and 
low frequency  per- 
formance. The grosser 
discrepancies which 
might be brought in 
bythe lenses are how- 
ever reduced by the 
restriction of the work- 
ing range due to the 
high frequency cut- 
Fig. 12. 
Contrast-reduction at 
stages in the produc- 
tion of a photograph. 
off of tl 
verge tc 
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