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How to solve Camera Exposure problems

Exposure meters indicate light intensity and are designed to help you get a correct exposure every time you take a photograph. When a light reading is taken the meter indicates the correct adjustments needed to the camera aperture and shutter speed settings. This sounds simple, as indeed it is, but not all subjects can be treated in a straightforward way. How would you tackle a backlit subject, a snow scene or subjects in deep shadow, for example? In such situations your exposure meter can well mislead you into giving the wrong exposure. ‘Correct‘ exposures are a matter of interpreting meter readings and applying them to the subject in hand.

Hand—held or TTL?

Many photographers use a hand-held light meter because of its accuracy and adaptability. Hand-held meters can also be used to measure incident light (light falling on a subject). A diffuser is clipped over the meter cell and a reading taken from close to the subject pointing at the light source. This is particularly suitable when the highlights_ are the most important tones in which to show detail.

For convenience, however, most people prefer to take reflected readings (light reflected from the subject) which can be taken by pointing a hand—held meter from the camera position, or measuring through the camera lens if the meter is built—in.

Hand-held meters are a little more difficult to use for reflected light. Most have a fixed acceptance angle which cannot take into account whether you have a wide angle or telephoto lens on your camera, both of which have different angles of view. Accuracy also depends on the user aiming the meter correctly at the area to be measured. The choice between hand—held and TTL meters is almost always decided by the fact that most modern SLR cameras have built—in meters. Through the lens metering means that you have one less item of equipment to carry, and it is quick and easy to take many of your readings at the position from which you will take the photograph. They automatically take in a wide or narrow angle of view depending on the lens fitted to the camera.

TTL meters can only be used for reflected light readings, however. You also need to know how much of the area shown on the focusing screen your particular TTL meter is designed to measure. Of course there is no reason why you should not have both types of meter, using one or the other depending on the particular problem.

Meter weighting

The area of the scene measured by a TTL meter depends on the positioning of the meter cell(s). A few measure a small ‘spot‘ area of the composition; some integrate the light over the entire area of the viewfinder and give an average reading; the great majority in SLR cameras are centre—weighted. A typical example of centre—weighting is where 60% of the reading is taken from the central zone of the viewfinder screen and the remaining 40% from the lower portion of the screen. This is known as bottom centre—weighting, and may give two very different exposure readings when the camera is held first horizontally and then vertically. If you rotate the camera vertically through 180° you may also notice two very different readings. Try this out with your camera so that if necessary you can compensate for the exposure readings given when you take vertical pictures.

Average readings

All meters are calibrated to give correct exposure for the amount of light reflected from a middle tone of the subject. (To be more exact this corresponds to a neutral grey card which reflects 18% of the light falling on to it—and this is considered to be an average tone.)

You will realize where problems arise from this averaging of light to a mid–grey tone when you apply the principle to specific situations. If a scene is predominantly dark the meter computes this to record it as a mid–grey tone by indicating that more exposure is required. To reproduce those dark areas correctly as dark a lot less exposure is actually needed. Conversely, if you are photographing snow the meter responds to the white surface by indicating that little exposure is necessary in order to reproduce the snow as a mid–grey tone. To produce white snow as white on film the exposure must be increased, probably by about two full stops. Learn how to interpret your exposure readings.

Spot readings

Spot or selective readings can be taken with an averaging meter used very close to the separate tonal areas in which you want to show detail. Simply get close to the subject and take a light reading from the important tone or tones only. A separate or TTL spot meter allows you to take selective readings farther away from the subject. A spot meter has a narrow angle of acceptance (perhaps only 1° of the whole scene). A separate spot meter has a viewfinder to allow general framing of the subject and the selective reading area is usually outlined. Because of its selectivity a spot meter can be extremely accurate, but you must understand what you are doing—carelessly aimed at the wrong part of your subject it can give totally wrong exposures.

Brightness range readings

When a meter reading is taken from a subject containing contrasting tones (brilliant white and the darkest black), an average reading will more often than not give incorrect exposure to the most important part of the photograph. It is also possible that the contrast range may be outside the latitude of the film you are using.

Take a selective reading from the darkest and lightest parts of the subject in which you wish to show detail. With many black and white films shadow and highlight areas within seven stops of each other will record accurately. For example, if the highlight reading indicates 1/60 at f22 and the shadow reading 1/60 at f2.8, select an exposure about half–way between (1/60 at f8) for the best possible compromise.

Colour films have far less latitude and particularly with colour slide film you should take a reading from the brightest part of the subject and bias your exposure towards that tone, letting the rest of the tones take care of themselves. Often, too, one tone is of key importance—such as the skin tone of a face, so step in close to the face to take a meter reading. If this is impossible take a reading from the back of your hand—as long as it is lit in the same way as the subject.

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