where the line spacing 
ing area”, the dodging 
he line spacing is con- 
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yarious materials 
e H & D curve 
al and influence 
siderably smaller, there is no dodging at 
all. 
According to the theory, the mean 
negative density should not have any in- 
fluence, but the measurements show a 
decrease in the amount of dodging with 
increasing density (figure 2). This is 
caused by the limited sensitivity of the 
feedback; the result is that on the Kel-O- 
Wat printer the dodging is negligible 
above a negative density of 2.0 D when 
printing on positive film. 
In a modified H & D diagram this ef- 
fect gives a "low frequency dodging 
curve" as shown in figure 3, whereas in 
the ideal case it should become a straight 
line. 
Now it is clear that the transmittance 
of the positive material has alsoan appre- 
ciable influence: if sensitized aluminium 
foil is used, no dodging can occur because 
no light can reach the feedback. With 
printing paper the situation is already 
much better and with film the influence 
of the material is still less. Consequently, 
the feedback and thus the amount of dodg- 
ing depends on the mean density of the 
negative and positive material together 
(in the case of electronic dodging these 
densities shall be measured with actinic 
light and in the case of the Kel-O-Wat 
with infra red radiation). 
In the graphical representation of the 
Contrast Transfer, these curves can be 
plotted on a log frequency axis (figure 5). 
Such a presentation demonstrates four 
basic aspects of dodging printers: 
1. The frequency where dodging starts: 
important is the position of this point 
with respect to the frequency range 
that will be used when judging the 
images. 
2. The frequency where dodging is at its 
maximum; it is seen that the “aver- 
aging area" has a diameter from 5 mm 
(Kel-O-Wat) to approx. 25 mm (Cin- 
tel). 
The possibility of shifting the total set 
of curves to higher or to lower fre- 
quencies; this is possible to a certain 
extent with all dodging printers. 
4. The maximum dodging as a function 
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Fig.5. The position of dodging printers in the Contrast Transfer Representation of A