The subject of your photograph isn’t what you think. It’s not the person, place or thing you’re framing up in the finder. The fundamental subject of your photo—of all photos, in fact—is light. What we capture with our cameras is not a record of a particular thing or person; rather, it’s the fleeting view of how that subject looked in a particular moment of light.

Light is at once our primary tool and our primary taskmaster. It dictates how we describe a subject: weak light, poor description; no light, no description at all. And what we know of any subject is a direct result of the character of the light we’re using.

Often we concentrate so much on what we’re photographing, we don’t pay attention to what the light is doing to describe that thing. But if we know, for example, how front and back light completely change the character of a subject, or how sidelight can give us a better three-dimensional description of our subject, we’ve got the knowledge we need to control our images.

© Bill Durrence Image 1 was taken with strong, direct sunlight on part of the scene and deep shadows elsewhere, requiring an exposure to hold the bright detail, causing the shadows to go very dark.

How Much
Light has specific, definable qualities, and those qualities hold true no matter if our light source is the sun, a room lamp or a flash unit. The first is quantity—simply, how much light do we have available?

The three elements of exposure control—shutter speed, f/stop and ISO—combine to give us the appropriate exposure value (EV). Not much light? Well, we can shoot at slower shutter speeds or increase the ISO or choose a larger f/stop. Or all three. Lots of light? We can shoot at higher speeds, cut the ISO and select a small f/stop. Of course, these changes will have their affect on the photo; for example, a large aperture results in less depth-of-field (the degree of sharpness in front of and behind our main subject) and slower shutter speeds mean we’re not going to be able to stop action in its tracks.

Because we live in a three-dimensional world, there’s seldom just a single quantity of light in a scene. Some parts of the scene are going to get more light than others; hence highlights and shadows. And where there’s an extreme range of light from the brightest to the darkest parts of a scene, getting a good exposure can become a problem.

How big a problem depends on the dynamic range or degree of difference between those brightest and darkest parts of the scene. A one stop difference in exposure equates to either twice or half as much EV; digital cameras can generally capture a five to six stop dynamic range.

But a bright sunny day can easily have a ten to 12 stop dynamic range, which makes it difficult to record all the detail in that scene in a single exposure.

If you’re in a situation like that, you may have to decide which part of the scene—the bright or dark areas—are most important and base your exposure on that decision, accepting the loss of detail in the other areas.

If you’re photographing a person during the middle part of a bright day, and she has dark shadows on her face, using fill flash can reduce the difference between the bright scene and her shadowed face. If it’s a landscape with dark ground and bright sky, a split or graduated neutral density filter can help compress the range of light into a more manageable exposure.

Another strategy is to record a good exposure for each of the areas—one for highlights and another for shadows—and merge the two images using editing software.

Image 1 was taken with strong, direct sunlight on part of the scene and deep shadows elsewhere, requiring an exposure to hold the bright detail, causing the shadows to go very dark.

In Image 2 the majority of the scene was in diffused, even light, and I was able to make an exposure that shows detail throughout.

© Bill Durrence In Image 2 the majority of the scene was in diffused, even light, and I was able to make an exposure that shows detail throughout.

A backlit situation, causing a lot of contrast in the extreme range of light from the bright sky to the darkened porch.

© Bill Durrence A backlit situation, causing a lot of contrast in the extreme range of light from the bright sky to the darkened porch. For Image 3, I exposed for the sky, which left the porch too dark to see detail easily.

© Bill Durrence For Image 4 I exposed for the porch, which washed out all the detail in the sky.

© Bill Durrence But for Image 5 I used my D300's Active D-Lighting feature to hold the sky and open up the porch detail, giving me a file that I could process for better results. In Capture NX2, I darkened the sky for a better blue and brightened up the porch so I could see the sign, evidence of the owner of the New Orleans homeowner's determination to recover: “Not 4 sale @ any $. I’m staying.”

In Image 6 I was getting patches of direct sun which caused dark shadows when I exposed for the highlights.

The second aspect of light is direction, and the direction the light is coming from determines the dimensional character of the subject or scene.

We could be dealing with front light, which comes from behind the camera and hits the front surface of the subject. Front light provides the maximum amount of information about a subject, but what it reveals often appears flat and uninteresting because everything is lit equally.

Then there’s back light. It comes toward the camera from behind the subject, and generally the only thing it reveals is the silhouetted shape of the subject.

Finally, there’s cross light, and it’s any light spilling across the surface of the subject. You can also call it side light or top light. It’s almost always preferable to front or back light because it causes a pattern of light and shadow that helps convey the depth and dimensionality of the subject.

How Big?
The third aspect is size, and the size of the light matters.Basically, the size of the light source relative to the size of your subject will determine whether you have hard or soft light.

Think of the light source as the last place the light is before it hits the subject. So if you’re using a flash and you point it directly at the subject, the flash is your light source. But if you point the flash at the ceiling and let the light reflecting from the ceiling illuminate the subject, the ceiling is the light source.

A smaller light source will often produce contrasty, harsh light. A larger light source will create a softer light—that is, a broader spread of light around the subject. On a sunny day, the disk of the sun, providing direct illumination, will be very small relative to your portrait subject; it will be a hard light source. On a cloudy day, a translucent diffusion panel between the sun and the subject, or a flash reflected into an umbrella, will be a larger light source than the person you’re photographing and will provide a soft light.

Remember, it’s the size of the light source relative to the size of the subject that determines if the light will appear hard or soft. A flash unit like the SB-800 Speedlight, used directly to illuminate a person, is a small light source—but that same flash used to light a butterfly will be a broad light source.

What Hue?
Finally, there’s the color of light, and that’s an issue of a camera’s white balance controls. All the light sources we think of as neutral—daylight, household light fixtures, flash—actually have some color bias to them. White balance will compensate for the different color of light being emitted by different light sources. The result of white balance control is that white objects appear white whether we’re photographing in direct sunlight, under incandescent lighting or using flash. In effect, digital cameras can process images according to the color of the light source. For the best rendering of the color of the light, choose a white balance setting that matches the light source or use a custom, pre-set white balance.Images 23, 24, 25 and 26 were shot successively at 7:53 p.m., 8:25 p.m., 8:44 p.m. and 9:08 p.m., with the white balance on my D2XS set to Shade. These photos show how the color of light can change in an otherwise unchanging scene.

Here are some things we can do to control our photographs under a variety of lighting conditions.Front light only? Try to move around the subject or have your subject pivot some to get more angle to the light relative to the subject.

Back light causing a silhouette? Use fill flash to light up the darker part of your subject, or expose properly for the bright background and let the subject deliberately be silhouetted.

Need to create sidelight? Easy. Rotate your subject or move the light.

How about reflectors and diffusers? If a person has strong light coming from behind her, or from the side, using a reflector opposite the light source will bounce some of the light back into the shadow areas and open them up a bit. If the light is falling harshly on the subject from the front or side, a diffuser between the light and the subject can soften the light and make a portrait subject more comfortable and less squinty.

How about bouncing the light? Bouncing a flash off the ceiling can help avoid the harshness and flatness of front light coming directly from the camera, and it also helps soften and spread the light and makes it easier to get a good exposure for a larger group of people since the light source (the ceiling) is equidistant from all the subjects.

Sometimes, with illumination coming through a skylight and other windows can mean setting the “correct” white balance to Shade (set in raw conversion with Capture NX2).

But I prefer the cool blue effect, achieved by shooting with the camera set for Incandescent white balance.

Bill Durrence is a professional photographer noted for his travel and location photography. He leads a number of photo workshops and is a featured instructor for the Nikon School of Photography.