----- Original Message -----
Sent: Sunday, May 05, 2002 6:53 PM
Subject: Pt/Pd printing with various
lights
A few weeks ago I posted some preliminary observations
on the use of different UV sources with Pt/Pd. As you may recall I
exposed a Stouffer TP 45 step wedge to paper coated with Dick Arentz' Pt/Pd
Mixture #7, using the following light sources: 1) 20 watt Phillips BL, 2) 20
watt GE BLB, 3) 75 watt URI Super Actinic, and a 1000 watt
HID-Mercury Vapor lamp. Today I read the densities of the tests and plotted
curves with Davis' Plotter program, with the following results.
BL
BLB
SA* HID
Speed Point
2.5
2.4
2.3 2.2
Exposure Scale
1.31 1.36
1.23 1.31
IDMax
1.17 1.20
1.23 1.31
* I also tested the 20-watt Phillips Super Actinic tubes and the results
were virtually identical to that of the 75-watt URI tubes.
*The HID-Mercury Vapor lamp was tested with a center filter which reduces
printing speed by about two full stops. Without the center filter this lamp is
faster than at least one full stop than any of the other lights.
For those not familiar with the above terms, here is some explanation of
terminology.
The Speed Point indicates the speed of the material and is
expressed here in relative terms. The higher the number the faster the
printing speed. The values are in log units where each value of 0.1 represents
one-third of a stop, or 0.3 corresponds to one full stop. Thus, the BL tubes
turned out in these tests to be one-third of a stop faster than the BLB tubes,
two-thirds of a stop faster than the SA tubes, and one full stop faster than
the HID-Mercury Vapor lamp (with the center filter).
Exposure Scale is the range between the minimum and maximum density
values required to print all of the tonal values. It is also expressed in log
values, with each 0.3 units corresponding to one stop. An ES of 1.3, for
example, corresponds to 4 1/3 stops. ES relates to image contrast, the lower
the number the higher the contrast.
IDMax is the value that corresponds to 90% of maximum black.
There have been quite a number of claims that Super Actinic tubes are
faster than BL and BLB tubes for printing in platinum. My tests show the
opposite. However, the SA tubes did produce images with more contrast than any
of the other lights.
Just for the record I ran the tests three times and the results were very
consistent. Over 95% of all readings of the three tests made with a specific
light source were identical, and no difference greater than log 0.02 was
observed.
Comments and questions about these tests are welcome.
Sandy King
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