Bright Field Lighting

Figure 7.2 is an example of the bright-field approach to lighting glass. The background dictates how we must treat any glass subject. On a bright background, we have to keep the glass dark if it is to remain visible.

If you have read Chapter 2 and the chapters following it, you have already guessed that the bright-field method requires eliminating all direct reflection from the edge of the glass surface. You also should be able to see why we need to begin this discussion by examining the family of angles that determines direct reflection from this particular subject.

Look at Figure 7.3, a bird's-eye view of the family of angles that can produce direct reflection on a single round glass. We could draw a similar diagram for each piece of glassware in our example photograph.

The family of angles in this diagram is similar to that defined by round metal in the last chapter. This time, however, we are not interested in most of that family. For now, we care only about the extreme limits of the family of angles, labeled L in the diagram. Light from these two angles determines the appearance of the edge of the glass. These limits tell us where the light must be if the edges of the glass are to be bright in the pictures or, conversely, where it must not be if the edges are to remain dark. Because in the bright-field approach we do not want the edge of the glass to be bright in the photograph, there must be no light along the lines marked L in the diagram.

7.3 The limits of the family of angles in this diagram are marked by L. Light from these two points determines the appearance of the edge of the glass.

Figure 7.4 illustrates one good way to produce a bright-field glass photograph. It is not the only way, but it is a good exercise that we suggest you try if you have not done it before. Look at the way the light behaves in each step. This will make it easy to predict what will work and what will not in any variation on this arrangement you decide to try in the future.

These steps work best in the listed sequence. Notice that we do not bother to put the subject into the scene until near the end of the process.

1. Choose the background. Begin by setting up a light-toned background. We can use any convenient material. Translucent materials such as tracing paper, cloth, and plastic shower curtains are a few good materials to try. We might also use opaque surfaces, such as light-toned walls, cardboard, or foamcore.

2. Position the light. Now, place a light so that it illuminates the background evenly. Figure 7.4 shows two possible ways to accomplish this; both can produce identical results. Usually the photographer uses one or the other, rarely both.

7.4 This is one way to produce the bright-field illumination used in Figure 7.2. We would rarely use both lights shown. Either lighting position works, depending on the background.

Dark Background or No Background->

Visible Background

Glass

Subject Light

Light for Opaque Background

Dark Background or No Background

Light for Translucent Background

Figure 7.2 was shot using a light behind translucent paper. This is a particularly convenient setup because it keeps the work space around both the camera and the subject free and uncluttered.

We can also use an opaque surface such as a wall for the background. If we do, we need to find a place to position the light so that it will light the background without reflecting in the glass or appearing in the image area. Putting the light on a short stand behind and below the glass is one good way.

3. Position the camera. Now, place the camera so that the background exactly fills its field of view. This step is critical because the distance from the camera to the background controls the effective size of the background.

The effective size of the background is the single most important consideration when using this technique. For this exercise to be most effective, the background must exactly fill the field of view of the camera, no more and no less.

A background that is too small is an obvious problem: it simply will not fill the picture. A larger background causes a subtler problem. A background too large will extend into the family of angles that produces direct reflection on the edge of the glass. Light from those points eliminates the dark outline that we need to define the edge of the glass.

If the background surface is so large that we cannot keep it from extending beyond the limits of the viewfinder (e.g., the wall of a room), we can also reduce its effective size by lighting only a small portion of its total surface or by covering part of it with dark cards.

4. Position the subject and focus the camera. Next, move the subject back and forth between the camera and the background until it is the desired size in the viewfinder.

As we move the subject, we notice that the closer it is to the camera, the more clearly the edges are defined. This increase in edge definition is not brought about by the simple principle that larger detail is easier to see. Rather, it is caused by the fact that as the subject moves farther from the lighted background, less light reflects off its edges. The closer the subject is to the background, the more the bright background falls within the family of angles that produces direct reflection to obscure those edges.

Now, focus the camera on the subject. Refocusing will slightly increase the effective size of the background, but that increase will usually not be enough to cause any practical problems.

5. Shoot the picture. Finally, use a reflection meter (the one built into most cameras is fine) to read the light on an area on the background directly behind the subject.

Bright-field illumination does not require a pure white background. As long as the background is any tone significantly brighter than the edges of the glass, then that glass will be adequately visible. If the glass is the only subject to worry about, we can control the brightness of the background by the way we interpret the meter reading:

• If we want the background to appear as a medium (18%) gray, we use the exposure that the meter indicates.

• If we want the background to photograph as a light gray that approaches white, we increase the exposure up to two stops more than the meter indicates.

• If we want the background to be dark, then we expose as much as two stops less than indicated. This will produce a very dark-gray background.

In this scene there is no such thing as "correct" exposure. The only correct exposure is the one that we like. We can place the tone of the background anywhere we like on the gray scale except black. (If the edge of the glass is black and the background is black, there is nothing left to record!) In practice, the lighter the background, the more graphically the glass is defined.

If we do expose to keep the background very light, we do not have to worry about extraneous reflection in the front surface of the glass. Whatever reflections exist are almost always too dim to be visible against the background. However, if we decide to expose to produce a medium- or dark-gray background, surrounding objects may reflect visibly in the glass. We will offer some ways to eliminate these reflections later in this chapter.

In principle, there is nothing particularly complicated about the bright-field approach to photographing glassware. Of course, we have used an "ideal" example to demonstrate the principle as clearly as possible. In practice, complications may occur whenever we decide to deviate from this ideal. For example, many compositions will force us to keep the glass much smaller, compared with the background, than in our exercise. That will reduce edge definition. Whether the sacrifice will be significant depends on what else is in the photograph.

Of course, understanding the principle and becoming familiar with why the ideal works gives us the understanding that provides the best solution in less than ideal situations. If a composition produces bad lighting, the ideal explains the problem and suggests a remedy. If a particular composition prevents any remedy, then the ideal tells us that, too. We need not waste time trying to accomplish what physics says is impossible.

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