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gamma or contrast index is plotted When the gamma or contrast index remains constant, the processing is consistent. CONTRAST INDEX 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. Index Curves 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 dots. 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 recommended agitation. gamma of 0.90. Find 70°F and follow the horizontal Advanced Photography Course |
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