(The possibility exists that the PG-1 performed poor because of this 
    
  
  
  
  
  
  
   
   
   
  
  
  
  
  
  
  
   
  
  
  
    
   
  
  
  
  
  
  
  
  
  
  
   
   
   
   
    
reason, and what with the colour adapter on the Kelsh-plotter? 
Does the flickering of fluorescent tubes disturb vision temporarily, 
until a defensive adaptation takes place? (Nathan, 1961). 
Other unconsious changes are the adjustment of the pupil diameter, 
which depends on emotion too, and the bleaching of the chemicals in 
the retinal receptors by the action of light itself. (Both have 
connections with the next group and with visual fatigue in the 
psychological group) | 
  
A panchro matic emulsion das a sensitivity of about P 
12 DIN = 12 ASA, if an exposure of 12 m Lux sec $ & 
produces a denelty of 6.1 Db over {og / 
  
  
what about He EYE 2 DIN or ASA 2 
  
The SENSITIVITY to white LIGHT is the most essential 
property of the eye. Physiologists study the basic 
Physiological mechanisms — as, for instance, the dark adaptation 
Aspects and the efficiency — but in photo-interpretation we 
are concerned with normal conditions, so we have to 
restrict to those properties which have relevance to 
   
our work. 
  
€T. 
The eye's (entrance) pupil is about 3 to 4 mm when looking through a 
Stereoscope - consequently, the instrument's exit pupil should be 3.5 
to 4 mm in diameter, otherwise the eye's mechanism is disorganized. 
Another point: the visual intensity range within one photograph or 
scenery which can be received by the eye is only 1 to 10. Areas which € © 
reflect less than 10% of the whitest areas are seen as completely black, , 
So please cover bright areas in and outside the print, if shadow details 
+ 
should be examined. 
[Some interesting points: What is the tolerable luminance difference 
between the left and the right-hand photographs under a stereoscope, 
for easy viewing? 1.5 or 2x? Do both pupils adjust in tandem to ihe 
same diameter, even if only one eye sees a bright image, the other 
viewing a dark print? They do, as can be found in front of a mirror, 
with one eye looking into a lamp. 
Operators are more tolerable with respect to a decrease in luminance 
of the image, if the magnification of the instrument is switched from 
1$ to 4$ times, as in the Old Delft, but if the exit pupil becomes 
too small, it is tiresome.]