To get additional copies of a color slide, you must either make several exposures of the original scene or make duplicates from the original slide. When the scene cannot be re-photographed, the only alternative is to make duplicates of the original slide.

Other than making a number of duplicate slides from an original, you can use the duplicating process to improve a photograph. The image can be made larger or smaller, the composition can be changed through cropping, the density of the duplicates can be changed from the original, and with the use of filters, the color of the reproductions can be changed.

In most Navy imaging facilities a camera designed especially for copying slides is used (fig. 8-6). This camera setup usually consists of a unit having a camera body and lens, bellows extension, light source, a copyboard, filter holders, and the necessary controls and switches. When slides are copied with a slide duplicating camera, the slide is transilluminated. This is the most common method of copying slides.

Exposure

Whatever method you use to copy slides, you must make exposure tests. The original slide you choose to make the tests should have average density and brightness and normal contrast. This slide should be retained as a reference slide. A full-frame slide of a color rendition chart (color checker) serves ideally as a reference slide. A color rendition chart allows you to visually or objectively compare a series of colors and densities of the original reference slide against the slide duplicate. To visually compare slides, you should use transmitted light and color viewing filters to judge the slides. The objective method is more accurate. A densitometer is used in this method. A densitometer is an electronic meter that measures the actual density of black-and-white and color materials.

Kodak Ektachrome slide duplicating film is recommended for slide duplication. This film is manufactured to provide lower contrast, less filtration with tungsten lighting, and it has good color reproduction characteristics.

The data supplied with the slide duplicating film or the Photo-Lab-Index provides information that you can use as a starting point for exposure tests. However, you should bracket the exposure at least one f/stop in one-half f/stop intervals on each side of the basic exposure.

Slide Handling

The original slide must be clean to produce high-quality duplicate slides. The smallest piece of dust or lint is magnified greatly when the slides are projected. Never touch a slide with your fingers. Handle the slides only by their mounts. Hold unmounted transparencies only by the edges. Dust or lint should be removed with low-pressure air or a camel-hair brush. If there are fingerprints or oily smudges on the slide, you can remove them with a soft, lint free pad or a piece of cotton dampened with film cleaner.

Slides should be placed in the slide duplicator base-side up. When you are duplicating the full frame

of the slide, you must place the slide on the copy stage horizontally, regardless of the composition of the slide. When a full frame view is not desired, you can crop or enlarge a portion of the original slide. When you change the camera or lens distance to alter the image size, be sure to refocus the image.

Examining Results

The duplicate slide should be laid on a light table and compared to the original. If you bracketed your exposure, determine which exposure provides the correct density. When none of the exposures are correct, the original must be recopied and given more or less exposure by changing the f/stop. The exposure time should not be changed. Again, bracket your exposure.

Color Balance

Color compensating (CC) filters are used in a slide duplicating camera. The CC filters are placed between the original and light source. By changing the filtration, you can correct the color balance of the duplicate slides.

After producing a duplicate slide with proper density, the color balance of the duplicate slide must be evaluated. When the color balance is off, you must change it through the use of CC filters and re-shoot the original. When the duplicate is extremely yellow, first check the slide duplicating light source. Most slide copy systems using tungsten light, have a "view setting" and a "filter setting." If the system was set in the view position, the CC filters were not in place. The unfiltered tungsten light produces a slide that is very yellow.

To judge the color balance of the duplicate slide, lay it on a light table, compare it to the original, and determine what color or colors are in excess. To do this, you should view the duplicate slides through various CC filters. A color print viewing kit is convenient for this purpose. When viewing slides through the various filters, look at the midtones, not the shadows or highlights. Color viewing filters are helpful in making color balance determinations. If a color rendition chart was used as the original slide, a densitometer can be used to directly compare the color balance of the original to the duplicate.

To adjust the filter pack for the color in excess in the duplicate slide, you should either subtract filtration of

Table 8-1. Color Compensating Filter Factors

the color in excess or add filtration of the complimentary color to the color in excess. The amount of change required is about the same as the viewing filter required to make the midtones appear correct.

For example, when a slide is over in blue and requires a CC20 yellow viewing filter to make the midtones appear correct, a CC20 blue filter should be subtracted from the filter pack. When a CC20 blue filter cannot be removed, a CC20 yellow filter should be added to the filter pack Your first choice should always be to subtract rather than add.

Adding or subtracting filters has an effect on exposure. To determine the exposure change required, you should refer to the operating instructions for the slide copier or consult a CC/CP filter factor table (table 8-1).

The number of filters used in a filter pack should be kept to a minimum. Do not combine all three filters. This only creates neutral density.

After processing, select the best exposure and use it as the basic exposure for future duplicates. When you copy other slides that are darker or lighter than the reference slide, adjust the basic exposure. Use one-half or one f/stop more exposures for slides that are darker than the reference slide, and one-half or one f/stop less exposure for slides that are lighter than the reference slide.

You should maintain a log of the different types of copy jobs completed in your area of responsibility. With the continual changes in photographic film, processes,

and equipment, you must always perform tests (whether it be standard copy or slide duplication) to achieve the highest quality product possible. Camera distance, light source (K), light distances, film type, filters, camera settings, and processes should all be included in the log. By maintaining a log, you eliminate the necessity for photographic testing every time a routine copy job comes into your work center.