Instruction manual

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In averaging metering, all the reflected light from the entire subject that fits
within the field of view of the meter is measured using a receptor with a
relatively wide acceptance angle. If the average reflectance of the entire
subject is close to 18%, the exposure reading will be close to the value
produced by an incident-light reading. For this kind of situation, this is the
fastest and easiest kind of reflective-light reading to make.
However, if there is a large bright or dark area within the camera's field of
view, or if there is any backlighting, these factors may cause the exposure
reading to be too high or too low. So, caution is needed in these situations.
In selective metering, measurements are taken so that only light reflected
from a specific, selected part of the subject falls within the acceptance
angle of the meter. This is achieved by using a receptor with a narrow
acceptance angle, or by placing the receptor sufficiently close to the
subject. Since the meter is not affected by light from other parts of the
composition, the selected part of the subject is reproduced on film at a
suitable tonal density. When the measured part has a normal reflectance,
e.g. human skin, then, as in the case of averaging metering, the exposure
reading will give a very similar result to incident-light reading. Thus, for
photographing subjects of normal reflectance, such as people, this method
offers highly accurate exposure readings. However, this method can cause
problems if you selectively measure very bright (high reflectance) or very
dark (low reflectance) subjects, because the meter assumes that the whole
image should have the same tonal density as the selected area. So take
special care about which part of a subject you select to measure when
using selective metering.
There are various advanced selective area metering methods, such as
the highlight standard exposure method, where an exposure reading is
taken of a bright (white) part of the composition; the shadow standard
exposure method, where a dark (black) part of the composition is
measured; and a method for determining exposure by evaluating the
contrast of the subject and then forecasting how it will come out on film.
To make full use of selective metering, refer to specialist books and
photo magazines. You will find that selective metering can give you
very precise control over exposure.
Reflected-light readings
Reflected-light exposure readings directly measure the amount of light
(luminance) reflected from the subject to the camera. Unlike the case of
incident-light readings, this method does not rely on the assumption of a
standard subject reflectance of 18%. Based on the measured amount of
light falling on the subject, the meter calculates the appropriate exposure
value for reproducing the subject on film at a suitable medium density
(midtone). This means that in reflected-light readings, all subjects,
regardless of their reflectance, i.e. regardless of whether they are bright or
dark (white or black), will be reproduced at the same tonal density
(midtone). For this reason, when making reflected-light exposure readings,
it is important to decide which area of the subject to measure, since the
reflectance will generally vary quite widely over the composition under
different conditions.
There are two basic methods for making reflected-light exposure readings.
These methods use different distances and angles between exposure
meter and subject. One method is "averaging metering," where the
exposure of the entire composition is measured (Fig. 4). The other is
selective metering," where illumination is measured only for a specific part
of the composition (Fig. 5).
Fig. 4 Averaging metering Fig. 5 Selective metering
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