Relaciones interpersonales en el proceso de elaboración de tesis

The photography of cut stones is a chal-lenge. Most people make the mistake of lighting them as they would any other subject, then they try backlighting them when they run into problems. Neither method works. If you stop to think about it, a faceted stone is designed so that the light enters through the top table facet, reflects off the pavilion facets on the back of the stone, and then exits out the table to the viewer's eye. Lighting for photog-raphy must follow the same path. This objective can be accomplished one of several ways.

If your light sources are small enough, as with the high-intensity desk lamps discussed in Chapter 6, they can be placed on either side of the lens, aimed at the stone. The film plane of the camera should be as nearly parallel with the table of the stone as possible (Fig. 16-1). This setup maximizes the effect and keeps the

155

PIERCED REFLECTOR

Figure 16-3 Setup for photographing gemstones with the lights aimed at reflectors place around lens.

Effects are improved if more than two lights are used, equally spaced around the lens. A deep lens shade should be used so that light does not fa¡¡ on the lens causing fiare.

stone from looking distorted or the culet (the apex formed by the junction of the pavilion facets) from appearing off center. The lights must be diffused and near-ly touching the lens. This technique works well with some stones, but the lighting is uneven and all the pavilion facets may not be illuminated. A better method would be to use a sheet of dif-fusing material with a hole in it for the lens to fit through (Fig. 16-2). The lights are on either side of the camera as before, but further back so as to illumi-nate all of the diffusing material (the lights themselves need not be diffused for this technique).

Another method is to have the lights on either side of, and aimed at, the cam-era(Fig. 16-3). Instead of diffusing mate rial with a hole in it placed around the lens, an opaque, white reflective material is used, such as Foam Core or cardboard.

Care must be taken not to let light spill

onto the lens itself. A long lens shade must be used to prevent this spillage. Cut the shade from a sheet of black con-struction paper or, preferably, black flocked paper. Form it into a tube that fits snugly around the lens and tape it te hold the shape. Cut it down in length se that when looking through the viewfinder, you no longer see it vignetting the i mage.

If your light source is too large and must remain above the subject, an alter-native method can be used. The camera is set up in the proper angle as before with a reflector fitted around the lens.

This time, the hole in the reflector is larg-er than before so that the reflector can be angled to reflect the light along the axil of view and into the table of the stone (see Fig. 16-4).

The master of loose, cut-stone photography is Tino Hammid (Plate

30), who gets incredible brilliance from his

sub-PIERCED REFLECTOR

Figure 16-4 If a single large light is used, it may not be possible to use the methods shown in Figures 16-1, 16-2, and 16-3. A pierced reflector can be angled so that the light is reflected along the lens axis to the stone.

jects. Joel Arem is known for his group shots of faceted stones (Plate 31).

When using any of these techniques, it is important to keep all reflections off of the table facet so as not to obscure the interior of the stone. A few subtle reflec-tions off crown facets are good to show that they are there and their quality.

Additional useful highlights can sometimes be added with small reflectors on either side of the stone. Instead of using a white reflector around the lens, it may sometimes be possible to use a matte aluminum reflec-tor when a little more punch is needed.

One of the main objects in pho-tographing cut stones is to bring out therr brilliancy. This effect is achieved by get ting as many of the pavilion facets to reflect the light as possible. Pavilion facets

that do not reflect light may be complete-ly black and create a disturbing "win-dow" Such windows may be hard to avoid especially with emerald and similar cuts. You may find with such stones that orientating the table parallel with the film plane won't produce the best results.

While viewing the stone, carefully change its angle until the optimum one is found.

Occasionally you'll run finto a stone that is i mpossible to get any color out of because it is too dark, or that you can get no reflections off the pavilion facets because they are cut too deep. In such cases, you can cheat a little by covering the back of the stone with foil, or just placing a small foil reflector behind it. You may sacrifice some detail of the pavilion facets, but you'll get color and brilliance.

157

Oblique illumination

Figure 16-5 Oblique illumination requires that the light be transmitted anywhere from 0° to close to 90° to the subject. (Koivula, 1981; courtesy of Gems and Gemology)

Not all the stones you shoot will be flawless. Examine the stone carefully before shooting to locate imperfections.

Orient the stone for shooting so that any flaws are minimized.

JEWELRY

jewelry presents the additional problem of highly polished metal (Plates 32 and 33). In addition to its reflecting every-thing around it (including you and the camera), any portion of the metal not reflecting a white reflector will go black.

The secret of jewelry photography is tent lighting. The subject has to be totally sur-rounded by white reflectors.

Start with a large diffused light source such as a soft box, then lean sheets of Foam Core right up against the soft box.

The camera will have to look through a hole in a reflector, and all reflectors will have to butt up against each other. Any gaps between reflectors will appear as black lines in the polished metal of the jewelry. Even if the reflectors butt up against each other, there may still be lines reflected. This problem can be dealt with by using white painter's masking tape to join the sheets together on the inside of the setup, facing the jewelry.

An alternative to reflectors is to liter-ally "tent" the subject. Create a conical form of diffusion material to place around the subject. A hole is cut in the material for the lens, and several lights are placed evenly around the diffuser.

There are several companies that make cloth cones for this purpose, but you can

Transmitted light

Figure 16-6 With transmitted light, the light passes through the subject, in this case, from the sub-stage light source. (Koivula, 1981; courtesy of Gems and Gemology)

easily make your own. When using cloth as a diffuser, you can use white Velcro as the seam closer. This seam can be opened anywhere necessary to allow access for the lens.

Some photographers have also experi-mented successfully with hemispheres of translucent white plastic as diffusers for jewelry photography. The hemispheres can be plastic storage bowls or the large spheres used as diffusers for domestic and public lights. Look in the lighting depart-ment of your local variety store for usable diffusers, but be sure they are neutral in color.

Sometimes reflectors are not needed on the far side of the subject and can be left out. This may be necessary so that the background grades to black or is just shaded. Be careful, however, that the highlights that define the top edge of the subject and separate it from the back-ground are not lost. You may be able to

create such a highlight by suspending a small reflector above and behind the sub-ject and not interfere with background

lighting.

INCLUSIONS

Inclusions in gemstones are of great interest to gemologists because their patterns "fingerprint" a stone, thus making it identifiable. They also aid in determin-ing mineralogical origins and whether or not the stone is synthetic. Direct or oblique illumination is seldom used in inclusion studies but is useful for opaque gems. According to Koivula (1981), direct illumination is good for defining some fractures and ultrathin liquid finger-prints. It is also good for bringing out interference colors. The best lights for such purposes are fiber optics, sometimes used in combination with other tech-niques, such as dark-field and polarized lighting (Fig. 16-5). Koivula also recom

159

Dark-field illumination

microscope objective

inclusion subject

microscope stage

dark-field reflector stone

holder

dark-field light shield rotated in to stop direct transmitted light

li ght source turned on

Figure 16-7 With dark-field illumination, a dark shield is placed between the subject and the light source below it, so that the only light to reach the camera is that refracted by the stone. (Koivula, 1981; courtesy of Gems and Gemology)

mends that gemologists create a file of slides illustrating inclusion characteris-tics for easy reference.

LIGHTING