example, a white card can be used to substitute highlight
areas of a distant scene. A dark or a black card can be
used to substitute a shadow area, an 18-percent gray card
can be used to represent middle gray, or the back or palm
of your hand can be used to substitute a gray tone.
When the substitution method is used, take the light
meter reading from the substituted item under similar
lighting conditions that exist in the scene. When the
scene is in bright sunlight, the substituted object must
also be in bright sunlight. Likewise, a scene in shade
requires a substitute light meter reading in shade.
You can use each of the methods discussed
previously with the substitution method. An 18-percent
gray card can be used for the integrated or averaging
methods, a dark and a light card can be used for the scene
brightness range method, a dark card for the darkest
object method, and a light card for the brightest object
method.
Bracketing Method
There are times when unusual lighting or subject
brightness prevents you from getting an accurate light
meter reading. In these cases, a good insurance policy
is to bracket your exposure. To bracket, you should take
one picture at the exposure indicated by the light meter,
and then take two more exposures: one at one f/stop
under the indicated exposure and another at one f/stop
over the indicated exposure.
When you are in doubt about the correct exposure
for a negative type of film, it is always better to
overexpose than underexpose. Even though over-
exposure produces excess densities in the negative, it
still provides a useable image that can normally be
corrected in the printing stage. When underexposed, if
the image does not exist on the film, no corrective
printing techniques can provide image detail.
When shooting reversal film (slides), you should
bracket in 1/2 f/stop intervals. Because the exposure
latitude of slide film is limited to 1/2 f/stop, you should
bracket in 1/2 f/stop increments, both under and over the
indicated light meter exposure reading. Color slides that
are 1/2 f/stop underexposed have more color saturation
and are more usable than ones that are 1/2 f/stop
overexposed and appear "washed out" and light.
TAKING LIGHT METER READINGS
When taking light meter readings, you must be sure
the reflected light that influences your light meter is
actually from the object you want to photograph. Stray
light, backlighting, large dark areas, and shadows can
all cause erroneous light meter readings. When using a
light meter, be sure that shadows are not cast from the
light meter, camera, or yourself. When a hand-held light
meter is used, the distance of the light meter to the
subject should not exceed the shortest dimension of the
object; for example, when taking a light meter reading
of a person's face that is approximately 9x6 inches, you
should hold your light meter about 6 inches from the
face of your subject when taking the meter reading.
When using a light meter that is built into a camera, be
sure to focus on the image before taking a light meter
reading.
CAUSES OF FALSE LIGHT METER
READINGS
There are a number of reasons why light meters give
erroneous or bad readings that produce underexposed
images. You can prevent these bad readings by being
aware of the conditions that cause them.
Light Entering the Viewfinder
Light entering the viewfinder and falling on the
viewing screen can cause underexposure. Most TTL
meters read the light falling on the viewing screen from
the lens. When strong lighting is coming from behind
the camera, it can influence the light meter. When an
occasional underexposed frame in an otherwise
successful series occurs, the cause may be light entering
the SLR viewfinder. Make a point of shielding the view-
finder if you do not have a rubber eyecup. When you use
a tripod, have the camera set on automatic and cap the
viewfinder to prevent exposure errors.
Incorrect Film Speed Setting
When the majority of frames on a length of film are
consistently underexposed or overexposed, the most
likely cause is you have the wrong ISO set on the film
speed dial. For black-and-white film and color reversal
film, it may be possible to compensate for this in
developing if detected before the film is processed.
Bright Subject
A bright object or highlight area can affect the
sensing area of a spot or center-weighted TTL meter.
This results in an underexposed image. To prevent this
from occurring, you should ensure the sensor is pointed
directly at a midtone within the scene, and use this as
the camera exposure. When you frame and compose
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