Photographic Exposure Made Easy

by Don O. Thorpe

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    (or How to Photograph a White Cat in the Snow and a Chimney Sweep at Night)

    Each time the New Era has a photo contest, there is a deluge of slides and prints from all over the globe. Many would-be winners don’t win because of flaws that could easily be avoided. Most of these fall under three main categories: (1) poor exposure, (2) lack of sharpness, and (3) poor composition. The biggest culprit is poor exposure. This article is written to help those of you who have problems getting the proper exposure. It is written for those of you who have some understanding of the basics of photography. Also, this article does not attempt to be a comprehensive or in-depth explanation of the zone system of exposure (there are volumes written about it that can be consulted for further instruction), but the basics are here.

    A washed-out, colorless slide or print, and even slightly overexposed areas in a normal looking slide, can ruin an otherwise prize-winning shot. Dark muddy colors and lack of visual texture and detail are attributes of the underexposed photograph.

    Let’s take an imaginary example: You’ve been shooting the school’s most important football game, hoping to get a shot that could lead off the sports section of your yearbook. You want something dramatic, not just the usual running and passing pictures. Long shadows from the bleachers cover the field in patterns of dark, and the team huddles for the final play of the game. The score is tied. The players shift slightly, and suddenly their yellow helmets come ablaze with color from a small patch of sunlight. Everything else is in deep shadow. You center the exposure needle carefully and manage to squeeze off a shot just before the team moves into its scrimmage position. What a shot—the bright yellow helmets set off by the contrast of dark shadows.

    You send the film to be processed and cross your fingers. A few days later the slides come back, and you nervously look for that one great shot. There it is! But something’s wrong. The yellow helmets are almost colorless. That great photo just isn’t.

    What happened? To understand what really went wrong, you need to know how the common light meter works. A light meter is merely an instrument that is sensitive to light; its needle moves in relationship to the amount of light that strikes the photo cells it contains. Most meters “read” all the light reflected from a subject and the background. This range of values, from dark to light, is “interpreted” by your meter as being an average, middle-gray tone. This means that most subjects containing a normal range of light and dark areas will be considered (by the meter) as middle gray. In these cases, you just line up the needle and shoot—good exposure every time! Well, almost … read on.

    What happens when your main subject is partially in bright sunlight and mostly in dark shadows, as was the case with the football helmets mentioned earlier? A light meter would be more influenced by the greater dark areas and would indicate the exposure necessary to make the shadows middle gray. Of course, this would overexpose the brightly lit subject; hence the colorless yellow helmets.

    There are several methods of solving these kinds of exposure problems. One method requires you to move in close and take a reading from just the main subject, then use that setting to photograph the entire picture area. However, this would be impractical in a situation like a football game. An alternative method would be to take a reading from an object similar to the main subject that is close at hand and in the same kind of lighting.

    But what if the entire subject is very dark or very light? If you use the exposure given to you by your meter in these kinds of circumstances, you will get grayed whites or grayed blacks respectively.

    The answer to this dilemma is something called the zone system of exposure. You can use an extremely simplified version of it and still get accurate results.

    The zone system allows you to compensate deliberately for light or dark subjects and all the in-between ones so that you have complete control of the final outcome. Using this system you can be sure of bright, deep colors, white snow, and black shadows.

    Let’s see how it works. First we divide a scale of values from black to white into five steps (see diagram). This is a zone value scale. Zone 1 represents the blackness of deep shadows, and black objects. Zone 5 represents white and very light highlights (not glaring white). Then there are the respective values in between. The key to understanding this system is to realize that zone 3 represents middle gray, the point of deviation. In other words, zone 3 is the zone your light meter is programmed to read. It is the average from dark to light of a normal scene.

    Looking at the zone value scale, we can determine which color matches with which zone. Then we can adjust our exposure in the camera to match that color. For example, the yellow helmets would probably fall between zones 4 and 5. This is one and a half zones away from middle gray. Now if each zone represents one f/stop of exposure, which they do, all we have to do is open up the camera lens (or shutter) 1 1/2 stops, and we’re ready to shoot for perfect exposure.

    We could approach it from the opposite side and read the shadow area (between zones 1 and 2); now we close down 1 1/2 stops. Interestingly enough, either adjustment would give you the same final exposure setting.

    All you are doing with this system is using any value from black to white to determine your exposure. You’re not stuck with middle gray. And since middle gray is not always available, you have a system that will give you correct exposure information at those times, too.

    Of course, there are times when you can use a substitute object that is middle gray to take a reading. Then you can just shoot with the reading obtained without adjustment. A lawn is usually close at hand and is very near to middle gray. You can also use clear, blue, northern sky in the same manner.

    However, it is still usually best to take your reading from the main subject itself and adjust to fit it. This will always give you the color saturation (deepness of color) that you want in your subject.

    When shooting with color slide film, most professionals underexpose 1/2 stop in addition to the adjustments made as described in this article. They feel the extra 1/2 stop gives them a richer color rendition. Sometimes I even underexpose one to 1 1/2 stops to achieve deep tonality and contrast. You should experiment to find what works best for you and your equipment.

    Experimentation and tests are invaluable to give you confidence and control. No two photographers see alike, and light meters and cameras are notorious for their differences. So you must shoot some tests to know where you and your equipment stand. Be sure to keep good notes and refer to them often till all these things become second nature. This all takes time and patience, but in the end you will be capable of coming up with those great shots almost every time.