Technical data

106
General information on exposure metering
Most scenes contain an even distribution of bright
and dark subject details and reflect an average of
18% of the light falling on them. This value of 18%
corresponds to an average grey tone to which
exposure meters are calibrated. Very bright sub-
jects, such as snow-laden winter scenes, sandy
beaches, whitewashed walls or a white wedding
gown, reflect more light toward the exposure
meter, tending to result in underexposure.
Predominantly dark subjects such as a black
steam locomotive, dark grey slate roofs, and
navy-blue uniforms reflect much less light, and
meters tend to overexpose.
This is the case unless a corresponding exposure
compensation has been set in advance or the ex-
posure has been measured selectively using a
section of the subject containing a representative
distribution of light and dark details (for more
information see the section " Setting an exposure
compensation ” on page 82).
You would for example meter on the bride’s face
and not on her white gown. A landscape shot with
a wide-angle lens should be metered with the
LEICA M7 pointing downward to exclude the
bright sky. Metering memory-lock allows this
technique to be used conveniently even when
using the aperture priority mode (for more details
see the section "The aperture priority automatic
exposure mode" on page 97).
If there is no suitable section of the subject for
metering when setting the exposure manually, a
compensation factor must be used, i.e. the expo-
sure time is extended by 2 to 4x or the aperture
can be opened by one or two f-stops.
White snow under a clear sky with bright sunlight
often calls for an exposure increase of 4x, i.e.
instead of the specified shutter speed of 1/1000s
and f/8, use 1/250s and f/8 or 1/1000s and
f/4. When photographing less bright subjects
such as a sandy beach, a compensation factor
of 2 is sufficient.
The reverse is the case for dark subjects.