Describe The Use Of A Daylight Exposure Table

Trick Photography And Special Effects

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1. We've talked a lot about how to control exposure by changing f/stops and shutter speeds, and we've talked a lot about equivalent exposures, but how do you find a correct exposure in the first place? Now you are going to learn just that. First you have to understand something about film. Film isn't just film. It comes in various speeds, and before you try to determine an exposure, you first need to know the film speed. "Speed" is just photographer's jargon for a film emulsion's sensitivity to light. It is determined by a complex and careful procedure established by the International Standards Organization (ISO). Every film manufacturer in the free world rates film using the numbering system established by the ISO.

a. The system is set up so that as the speed numbers double, the film sensitivity also is doubled. For example, ISO 400 film is four times as sensitive to light as ISO 100 film. (How many stops is this?) Here's another example: If you are shooting ISO 125 film and switch to ISO 64 film, how would you adjust your exposure? (Right, you go on as before, but you open the lens exactly one stop.) That's why ISO 400 film is "one stop faster" than ISO 200 film.

b. The ISO system also gives you a really handy way of figuring out outdoor exposures without using a light meter. Look at Table 1-7. You use this table by first setting your shutter to 1 over the ISO number. That is, if your film is ISO 125, start with 1/125 second. If the ISO is 64, use the closest speed you have, i.e., 1/60 second.

2. Now that you have your shutter speed, you need to determine how bright your subject is. That's the vertical column at the left side of the table. Here is a breakdown of what those subject brightness labels mean.

a. Average subject. An average subject is one that reflects about 18 percent of the light striking it and absorbs the rest. This category includes people in medium-colored clothing, most buildings, landscapes with trees, and street scenes. The majority of photographic subjects are of average brightness.

b. Dark subj ect. A dark subject reflects only about 9 percent of the light striking it and absorbs the remainder. Because it is only half as bright as an average subject, it needs twice the exposure. Military tactical vehicles, weapons, people in dark-toned clothing, animals with dark fur, and very dark or black-looking stone are all dark subjects.

c. Bright subject. A bright subject reflects about twice as much light as an average subject. Consequently, it absorbs a much smaller percentage of light. A bright subject requires less exposure than an average subj ect -generally one stop less. Typical subjects in this category are fair-skinned and light-haired persons, people in light clothing, animals with white fur coats, and light-colored buildings.

Daylight Exposure Table
Table 1-7. Estimating exposure outdoors

d. Brilliant subj ect. A brilliant subj ect reflects about four times as much light as an average subject and absorbs relatively little light. A brilliant subject requires much less exposure than an average one -generally two lens stops less. Snow-covered landscapes, people in white clothing on a white sand beach, a white sailboat against a blue sky, and white painted buildings are all brilliant.

3. Now you have shutter speed and subject brightness. Look at the horizontal row at the top of Table 1-7. There are five classes of illumination: bright sun on light sand or snow, bright sun, hazy sun, cloudy bright, and open shade.

a. Bright sun. This one is self-explanatory. The sky is clear, and the sun is far too bright to look at directly. Shadows are sharply defined, with a hard edge. This type of light is excellent for landscapes, architectural subjects, and anything else for which you want hard, clear definition. Because of the hardness, it is not usually a good type of light for portraits unless a hard effect is what you are looking for. Sometimes the contrast between the sunlight and shadow is so great that shadows look black and featureless, because the brightness range is so great the film cannot record it all.

b. Bright sun on light sand or snow. Because they act as reflectors, light sand or snow increases the amount of light on a subject about a half-stop more than under normal conditions. Otherwise, all the conditions but one described for bright sun apply. The one exception is contrast, which is usually fairly low because the reflections from the sand or snow casts light into the shadow areas, filling them in.

c. Hazy sun. On a hazy day, the sun is partially obscured by haze or thin high clouds, but the sun's disc is still clearly visible and bright. Shadows are still easy to see, but they are slightly diffused or soft and not as clearly defined as in bright sun. Because of the haze, distant scenes may be obscured. This can often be used to good effect. Hazy sun is often good for portraits of people whom you wish to portray as rugged. The shadows are clear enough to bring out skin texture and facial lines, but are often soft enough so that the shaded areas of the picture still show some detail.

d. Cloudy bright. On a cloudy bright day, the sun's disc is still visible, but barely so, because clouds almost hide it. To the eye, the day may seem very bright, but this lighting needs about two stops more exposure than bright sun. This lighting still produces visible shadows, but they are weak and have very soft edges. Cloudy bright conditions are excellent for general portraiture and scenes of short or middle distances. Distant scenes which include a lot of sky can be a problem because the sky, which is still very bright, will often be overexposed and will come out in a print as a featureless white. If you make prints with white, unexposed borders, it is often impossible to tell where the sky ends and the borders begin - they are both pure white.

e. Open shade. On cloudy dull days, the sun can't be located in the sky because it is entirely obscured by clouds. There are no shadows at all, except very faint ones under automobiles or picnic tables. The lighting is extremely soft and is good for portraits of children, women, or any other subjects you wish to show as softly as you can. Sometimes the light is too soft, and subjects appear flat because there are no shadows to give the viewer a feeling of depth. That's why this kind of light is often referred to as "flat". Open shade looks much like cloudy dull conditions, except that it can be found on a clear sunny day. Open shade is shade which is open to a lot of sky, but shaded from the direct rays of the sun. The shady side of a building is an excellent example. But there must be overhead skylight. Shade under a low, densely leafed tree or an awning is not "open". Cloudy dull and open shade need three stops more light than bright sun does.

f. The daylight exposure table helps you determine what setting to use outdoors. Once you have decided what the subject's brightness is and what type of lighting there is, you set the aperture to the setting where the rows and columns intersect (Table 1-7).

4. One final adjustment might need to be made. If the subject is fully lit by the sun behind you, you're all set; use the exposure exactly as it comes from the table. This is called front lighting. But if the sun is to one side shining across the subject so that part of it is lit by the direct rays of the sun and the rest by the light of the sky, you should open your lens one stop from the table's recommendation so that the shadows still show some detail; this is side lighting. If the sun is behind your subject and shining in your face, then you should give two stops more than the table indicates. This is called back lighting. Of course, if the lighting conditions are cloudy dull or cloudy bright, the shadows are so weak you don't have to worry about making these corrections; they are necessary only in bright or hazy sun.

a. You don't have to memorize Table 1-7, but it would help. What you must remember is what the subject and lighting conditions described above mean; then, think of the "sunny f/16 rule". That is, in bright sun with an average subject, use a basic exposure of 1/ISO at f/16. Then make adjustments based on the subject brightness and lighting conditions you are actually photographing.

b. One final caution about using this table. It only works outdoors, and then only two hours after sunrise until two hours before sunset. Beyond these times, the lighting conditions can vary widely and the table is almost useless.

Learning Event 6:

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