SINTAXI

Lighting of the background is important too. If the subject is directly on the back-ground material, they are lighted at the same time. Some control can be exercised over the lighting of the background.

Most specimens are shot sitting directly on a background material such as colored paper or cloth that curves up behind them. Lighting the background is often opposite the rule of specimen lighting about being light on top and dark on the bottom. This reverse lighting provides a contrast where the brighter specimen top is not lost in bright background, nor the dark base in a dark background.

Preventing the specimen and back-ground from blending together can be achieved by keeping the main light aimed at the specimen and foreground and not en the curved upright portion of the background. This lighting is usually accomplished by tilting the main light forward so that the shadow its housing throws partially shades the background.

You can also achieve, or enhance, the effect by hanging a sheet of black con-struction paper off the back of the light so that its shadow falls across the back-ground.

One of the goals in this technique is to achieve a smooth, not sudden, grada 74

tion from light to dark (Fig. 8-2). The high-er the light source is from the background, the softer the transition will be. A diffused light source will also soften the transition.

One last factor to be considered is the angle of view. The lower your angle of view, the sharper the transition will be, and, conversely, the higher your angle of view, the softer the transition will be.

When angling your lights toward the camera, you run the risk of shining them right in the lens and causing fiare that will ruin the photograph. Flare can manifest as an overall image degradation due to loss of sharpness and contrast, or as bright streaks and "ghosts" in the image.

To eliminate this problem, hang a sheet of paper off the top of the lampshade so that it keeps the light off the lens, as illus-trated in Figure 8-3.

The use of a good lens hood at all times also reduces the risk of lens flare. If you cannot get a lens hood for your par ticular lens (especially if it is a specialized macro or enlarging lens) you can easily make one. Take a strip of black construc-tion paper and wrap it snugly around the end of the lens, then tape the overlapping ends. Look through the camera with lens and lens hood attached. If you can see the lens hood in the corners of the frame (this is called vignetting), cut it down in length until you can no longer see it in the view finder. If you are using the lens on extension tubes or bellows, you may find that at shorter extensions the lens shade may be too long and vignette the picture because of the wider field of view at shorter extensions.

The use of barn doors on the main light can also control lighting of the background. Another technique is to

spotlight the specimen ( Plate 9).

These techniques all basically create a graded lighting of the background, but there's more you can do. Once the back ground is darkened you can light it sepa-rately with spodighs or microscope lights to create spotlight or halo effects.

Background treatment is further dis-cussed in Chapter 11.

TRANSMITTED LIGHT

At the beginning of this chapter 1 said I would discuss techniques having to do pri-marily with direct lighting. There are many cases, however, where transmitted light (light traveling through the speci-men) is of great use.

Besides external reflections, there are internal reflections. The light will often reflect off of internal fractures and inclu sions, adding great depth and interest to a specimen. You may wish to concentrate

on there interior details on purpose. Keep exterior lighting to a minimum, and aim a bright concentrated light, such as from a microscope light, into the back or side of the specimen. This approach is very effective in minerals with inclusions or phantoms. Translucent, strongly colored minerals with this "piped in" lighting seem to glow. The effect can be very dra-matic (Wilson, 1974). The effect also can be misleading if done to excess. I have heard of many instances where people

were very disappointed to see a specimen after viewing its backlighted photograph.

In real life, the specimen did not have the brilliance and color the people were led to expect by the photograph.

When using this technique, you must also be careful not to have too much of

the backlight spill over onto portions of the crystal visible from the front. A small amount can create the useful edge light-ing previously discussed. Too much can create burned out highlights.

Another useful and more subtle tech-nique is to place a reflector behind the specimen. Aluminum foil is best for this as it can be carefully cut and folded to match the shape of the specimen. Be sure that it cannot be seen from the front, and angle it so that if the specimen were not theie, it would be reflecting your main light

right into the lens. The advantage to using the foil for backlighting is that the effect is subtle and theie is no problem with the light spilling around the edge of the specimen creating burn-outs. It can also more evenly illuminate a specimen than a spot- or microscope light can.

These backlighting techniques have their limitations. Backlighting cannot be used on crystals that lay flat on the matrix. Both techniques work best with translucent crystals. It is the inclusions and defects that scatter the light, making a crystal's color intense. A problem with absolutely transparent, gem crystals is that you can see right through them and see the reflector. Backlighting a flawless gem crystal will have little effect on it because most of the light passes right through it.

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L ight is the most important

ele-ment in photography and in order to use it to advantage, we must measure it accurately with a light meter. Exposure meters have light-sensitive metering cells that measure the intensity of light falling on them, and then translate this information into suggested f-stop/shutter speed combinations.