PHOTOGRAPHY HAS UNDERGONE an earth-shattering sea change in its transition from film to digital. At the same time, the foundation of photography—light—remains the same. Photography literally means "light writing," which means that photographers are light writers. The ability to bend light to our vision is what makes us photographers. After all, anyone can buy a high-quality digital camera. Very few can light a subject well. You might say light writers light right.
Eye versus Camera
It all starts with how our brain sees light—and how the camera records it. Adding to the complexity is that what your camera records may not be possible to reproduce on the printed page. Here's how it breaks down.
The range of light on a bright sunny day is too wide to capture detail in both the shadows and highlights with a camera, whether digital or film-based. This fact doesn't seem to jibe with how the brain handles visual processing. When we look at a scene that has too wide a range, the brain looks first at the brightest areas. It remembers the details in the highlights and midtones, then it tells the pupils to widen to see what's in the shadows. The brain combines the two images—the lightest and the darkest—in real time, allowing us to think we see a wider range of brightness than we really do. In other words, the brain is doing Photoshop on the fly. Who knew?
Digital cameras can record a wider range of brightness than film can. That's good. The problem is that printers can't begin to reproduce the brightness range of film, much less that of digital. There is a range of brightness of light that can be printed that will give detail in the highlights and shadows at the same time. A good inkjet printer can hold detail if the image has RGB numbers of around 25 to 40 in the shadows and a range of 242 to 249 or so in the highlights. Printing from Lightroom works the same, except the RGB values are presented as percentages. From 7% to 95% will provide a brightness range of reproducible shadow and highlight detail. Your printer, ink, and paper combination will also affect the results. Newer printers can extend that range on glossy or luster papers. Fine art papers, matte, watercolor, or canvas have smaller ranges between highlight and shadow detail. If the RGB number reads lower or higher when sampled, detail must be sacrificed in either the shadows or the highlights. Digital cameras today have sophisticated built-in software to help with setting exposures that return fairly consistent quality images. The algorithms tell the camera which end of the brightness range to favor and which to discard. The usual bias is to keep detail in the highlights and let the shadows go dark. It's a good compromise for point-and-shoot situations.
Specular highlights—catchlights in the eyes, or sun glinting off a chrome bumper—are reflections of the source of light. They have no detail and don't count when considering the tones for printing. When printed they appear as paper white.
The photographer's job is to use light to control (and often compress) the brightness range so both subtle shadows and highlights shine through. Lighting starts with exposure.
Exposure and metering
Exposure, or the amount of light that hits your camera's sensor, reveals the diffused value or true tone of the subject. That's simple to say and a bit trickier to do, especially with a digital camera. There are two methods of reading light to determine exposure. One measures light after it has already lit the subject, bounced off, and is on its way to the camera. The other measures the light before it hits the subject. The first method is reflected metering. It interprets the amount of light that has already illuminated the subject. The second is called incident metering because it measures light before it reaches the subject. Let's look at each in turn.
Reflected meters are the kind that are built into cameras. This type of meter sets a default exposure that returns a middle gray value, or RGB numbers of around 127 (Lightroom: 50.2%). If your camera's meter reads a white value, the meter tells the camera to underexpose the scene by 2⅔ stops so that it yields the desired middle gray. Pointing the meter at a black value results in a two-stop overexposure so that it once again results in middle gray (Figure 4.2). Reflected meters return an exposure value equal to 12.5% gray on any value they read.
Look at the average RGB numbers for the three separate exposures shown in Figure 4.2. Each average is taken from white, gray, and black areas in the scene. The results of the separate exposures for the three swatches are: white: 129 (LR: 51.3%); gray: 130 (LR: 51.1%); and black: 127 (LR: 50.5%). The only exposure that can be called useful is that made by reading the gray patch. To make accurate reflected-meter readings, it's common for photographers to carry a neutral gray card or the GretagMacbeth ColorChecker Gray Scale balance card, shown here. If a card is not available, worn asphalt and green grass can do the trick as both are close to 12.5% gray.
Incident meters—separate handheld devices not built into the camera—are the most effective meters for setting proper exposure because they measure the light falling on a subject. Unlike reflected meters, they are not affected by the tonality of the subject. Incident meters are held at the subject's position (Figure 4.3). The dome receiving the light is aimed at the source of light. The reading is then set on the camera. This exposure setting is the diffused value. Once the exposure readings are entered in the camera, everything else in lighting is subjective and done at the photographer's whim for the desired effect.
Contrast is the difference between highlights and shadows. When the contrast range is greater than four f/stops from darkest to lightest, the result will be out of the range most printers can handle. Usually the result is solid black shadows (Figure 4.4). The shadow area in the photograph of model Marie Friemann shows a reading well below the 25–40 minimum RGB range that's required to show detail. This example is a high-contrast photograph. The difference between the lightest and darkest areas is well beyond a reproducible four stops. The shadows are blocked up so much as to be black.
Adding light to the shadows lowers contrast. My assistant, Holly Jones, holds a reflector panel that bounces light from the source back into the shadows at Marie's right (Figure 4.5). As a result, detail within the shadows is revealed (Figure 4.6). The Red channel now reads 69 (LR: 21.3%). Her hair, forehead, cheek, ear, and the texture in the shadow area of the background are revealed. The exposure remains the same, as no more light is coming from the source.
One of the reasons photographers love the light in the latest part of the afternoon, just before the sun dips below the horizon, is its directionality, warm color, and lower contrast. The shadows are filled in by the open sky.