This is why it is generally advisable to rely on the diaphragm (f/stop) when adjusting for print density
while keeping the exposure time constant.
d. Reciprocity failure. The law of reciprocity is the law of exposure, i.e., Exposure = Intensity x
Time (E = I x T). In theory, any combination of light intensity and exposure can be used as long as it
produces a good exposure. This theory is true in most cases. However, exposures of extremely long or
short duration sometimes cause a shift in the emulsion layers. This is especially true when working with
color materials, both film and paper. Since you are working with three emulsion layers, you must be
very careful with your exposures. In effect, if you encounter reciprocity failure, you have an apparent
loss of film speed, and the colors in the emulsion layers will shift, meaning the colors are not rendered in
their true colors.
2.
Manufacturers recommend that for short term storage, (3 months or less), color papers should be
kept at a temperature of 50 degrees Fahrenheit or lower. For long term storage, (4 months or more),
color paper should be kept at 10 degrees Fahrenheit or lower. In either case, paper should be removed
from storage the day before you intend to use it. For best results, process the exposed color paper as
soon as possible.
Learning Event 2:
EXPLAIN THE USES OF COLOR PRINTING FILTERS
1.
The major difference between black and white and color printing is that black and white
negatives and printing paper have only one emulsion layer. Therefore, there is only one image. Color
negatives and color printing papers have three emulsion layers and, therefore, produce three images.
The three emulsions are converted to colored dyes after processing as explained in Lesson 1. The three
dye images in color paper are controlled by the exposure time in the printer and the color of the light that
is transmitted. In other words, the image is controlled by exposure and filtration.
a. A combination of dye images in the negative plus any filters you use in the printer combine
forces to control the final dye image in the color print.
b. There are two methods of exposing Ektacolor paper using the color printer. They are tricolor
or additive printing and white light or subtractive printing. The tricolor method is very time consuming
but is still a valid method of making prints. In the military, we normally use the white light method of
making color prints.
2.
The tricolor or additive color process. Exposure of color film, and to a more limited degree color
printing paper, applies the principles of the additive color process. The additive process uses the
primary colors of blue, green, and red.
a. When equal parts of blue, green, and red light are projected from separate projectors and are
partially superimposed on a screen, you see in the area of overlap of all three colors, white, as shown in
Figure 2-1.
11
Previous Page
