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Exposure measurement
Figure 10.16 Alternative methods of using a hand meter: A: direct, general reading from the camera. B: close separate measurements of lightest and darkest important areas, then averaging the two light readings. C: reading off a mid-grey card receiving the same lighting as your subject. D: incident-light reading through the meter’s diffusing dome. Meter here points from subject towards camera
1 For a general reading, you just point the meter from the camera towards your subject. The meter’s angle of view usually approximates that of a standard lens, so it ‘sees’ a matching area of the scene. The meter averages out all the various light values this contains (naturally being more influenced by the values of large subject areas than small ones). Then it gives an exposure reading that would place this single imaginary ‘average brightness’ about midway between under- and overexposure on the characteristic curve. Like using a compact camera with an overall reading meter, the trouble with a general reading is that the most important element in your picture is not always the largest. The face in a portrait may occupy less than 50 per cent of the picture area, the rest being background (Figure 10.14). In one version you might use a dark background and in another a much lighter one, without any change to the illumination on the face. Yet the meter, taking over 50 per cent of its reading from the background in each case, will give low reading for the first shot and so overexpose face skin tones, and a high reading for the second version making the face underexposed. A general reading is therefore only satisfactory if your shot has a fairly equal distribution of light and dark areas in which you want detail. Subjects like Figure 10.19 (top), for example. It often works with softly lit landscapes (tilt the meter down slightly to read less sky and more land, if this is where details are more important). Another problem is that zooming or changing to a different focal length lens can make camera and meter have very dissimilar angles of view. Used from the camera position the meter then reads a larger or smaller area than is included in your picture. 2 For a brightness-range reading, you first decide which is the lightest and which the darkest part of the scene where detail must still just record. Take separate readings of both, bringing the meter sufficiently close in each case to exclude everything else. (Don’t cast a shadow on to what you are measuring, however.) You next split the difference between these light measurements and read off exposure for the resulting figure.