where the line spacing
ing area”, the dodging
he line spacing is con-
y paper
High freq.
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low freq.
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f dodging printers
Xposure
paper
exposure
cked dia-pos
exposure
paper
exposure
cked dia-pos
Y RANGE
for contact
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
eo
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Fig.5. The position of dodging printers in the Contrast Transfer Representation of A
