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changing either the intensity or the time. known. The intensity of the light must also be known. The time of exposure should correspond closely with actual photographic practice and must remain constant over long periods of time. In addition to this, the color temperature must be known, must remain constant, and must correspond closely to the quality of light that is likely to be used in practical photography. These qualities allow the test strip to be exposed under conditions as close as possible to those that occur in practical use. When you base sensitivity measurement on a consistent factor that is known, the response of light-sensitive emulsions, under practical conditions, is predictable. Thus various emulsions may be compared to each other. You know that emulsions often change in apparent sensitivity (speed) with a change in the spectral composition (color) of the exposing light. Processing also has an effect on the speed of emulsions. about 3200 K. The color temperature of sunlight is about 5400 K. Therefore, you may need a filter to alter the color of the lamp, so it is equivalent to the spectral energy of sunlight. commonly in Navy imaging facilities, permits you to change the exposure times as well. The exposure can be changed from 1/100 second to 1/10,000 second. that are already known. These are generally arranged in steps from low to high. A part of the strip is left unexposed, so the gross density of the material itself may be determined. device should be able to produce an exposure range that conforms closely to that found in actual practice, to be accurate, to be consistent, and to have no significant effect on the color quality of light. A step tablet is used in a sensitometer for this purpose. are comprised of a series of neutral-density filters with densities that range approximately from 0.05 to 3.05. On an 11-step step tablet, one f/stop exposure difference (or 0.30 density difference) exists between each step of the tablet. On a 21 -step step tablet, a 1/2 f/stop exposure difference (or 0.15 density difference) exists between each step of the tablet. Selection of a step tablet should be based on the emulsion latitudes and contrast differences in pictorial and copy films and papers. A 21-step step tablet is used normally for long-scale films, and a 11-step step tablet is used for short-scale films and printing papers (fig. 2-2). temperature, agitation, and chemical activity. This holds true whether the material is black and white or color. Black-and-white control strips are normally made in the lab, while color control strips are obtained from the manufacturer of the material being processed. film or a leader. To reduce the likelihood of bromide drag, ensure the leading edge of the sensi-strip has received the least amount of exposure in the sensitometer. Following this procedure, the strip goes through the processing machine tanks with the rest of the roll and receives the same processing. Remember film are important if the process is to maintain high standards and uniformity of results. Each step in the entire process must be carried out as carefully and as systematically as possible with uniform times and handling techniques in each step from exposure to Advanced Photography Course |
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