gamma or contrast index is plotted When the gamma
or contrast index remains constant, the processing is
light sources, require a lower CI. For these systems,
a lower value may be more suitable. The best gamma
be determined only through practical tests. These
tests can be made by developing several equally
exposed films to different gamma or contrast-index
prints best on your printing system is then used.
time of development required to reach a desired
gamma or contrast index. Time-gamma and
time-contrast index charts can be made to show the
maximum gamma (gamma infinity) or maximum
contrast index (contrast index infinity) obtainable with
a given film-developer combination.
the family of curves is plotted. The horizontal axis of
the small graph indicates time of development in
minutes and the vertical axis indicates gamma or
contrast index, as appropriate. The gamma or contrast
index obtained from each sensitometric strip of the
film being tested is plotted against the time required
to produce it by placing dots in their proper position
on the graph. A french curve is used to connect the
graph, and read the development time needed from the
choose a higher gamma, or contrast-index value.
contrast index. The processing latitude may be found
by determining the minimum and maximum gammas
or contrast indices that are acceptable.
increases, gamma or contrast index also increases.
This increase is rapid at first and then increases more
slowly. After a period of time, there is little increase
in gamma or contrast index, even though development
is prolonged This indicates that for any particular
emulsion and development condition, the higher the
gamma or contrast index, the greater the processing
latitude. This also indicates that the lower the gamma
or contrast index, the more precise processing
conditions must be to obtain uniform development.
is the temperature of the developer. The higher the
temperature, the greater the activity of the solution.
As the temperature drops, the developing time must be
increased. Since gamma or contrast index must also
be considered, typical time-temperature charts include
a gamma and/or contrast-index value that varies
according to development time and temperature. By
consulting a time-gamma or a time-contrast index
temperature chart, you can determine the proper
developing time under varying conditions. These
charts are published by film manufacturers and can be
seen throughout the Photo-Lab Index. Figure 2-11 is
a typical time-gamma chart. To use a time-gamma or
time-contrast index temperature chart, follow the line
until the desired gamma or contrast-index line is
intersected. From this point, drop straight down to the
time of development line. The intersection of the
vertical line and the time of development line
indicates the proper developing time at the
gamma of 0.90. Find 70°F and follow the horizontal
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