light and changing its exposure recommendations as you move the camera. In
most cases, this leads to the best possible results. However, there are times when
you will want to establish an f-stop and shutter speed based on reading one or
another specific area of the scene, and maintain these settings as you recompose
and shoot the picture. For these times, you can use autoexposure lock (AE lock),
a feature available on most current 35mm SLRs and some other camera models.
You usually activate AE lock with a button or a switch of some sort on the
front or back of your camera. Take your exposure reading in the area of the scene
that is most important to you, hold the button down or press the switch to lock
the settings in, then compose and take the picture. On some camera models, you
also can lock autoexposure settings with light pressure on the shutter button.
Here are some examples of when you will want to use AE lock. If your portrait
subject is backlit against a bright sky, read the light from your subject only,
avoiding the sky, by pointing your camera down until the sky doesn’t show up in
the viewfinder; hold that reading with AE lock, recompose the scene so the sky is
in the viewfinder, and take the picture.
Or if you want to compose your subject so it is on the edge of the frame, point
the camera so the subject is in the center of the viewfinder, take the exposure
reading, and lock in the recommended f-stop and shutter speed. Then recompose
the scene any way you want and take the picture.
might have to add two stops more exposure: f/4 at 1/500 or f/8 at 1/125 (or the
equivalent).
If the scene has mostly dark areas, reduce the exposure a little from what the
meter suggests, either by making the lens aperture smaller or making the shutter
speed faster. Here, too, using less exposure with a mostly dark subject may
seem counterintuitive. But again the meter always provides settings that render
the subject middle-gray—and here, you want dark tones, not grays. Exposing
the film for less time will make dark areas lighter than gray on the negative and
darker (denser) in the print.
With dark areas, usually a one-stop decrease or less from the indicated meter
reading is all you will need; cutting back by more might lead to underexposed,
hard-to-print negatives. So if the meter suggests f/4 at 1/60, use f5.6 at 1/60 or
f/4 at 1/125 (or some other equivalent) instead.
Note that some photographers are reluctant to deviate from the meter’s
suggested exposure, but it’s important to understand that adjusting the meter
reading by decreasing or increasing exposure in such cases does not mean you
are necessarily underexposing or overexposing your film. Rather, you are simply
adjusting exposure to compensate for a meter reading that would otherwise be
inaccurate.
Use a gray card. You can use a gray card to provide a middle-gray tone for your
meter to read, thus entirely avoiding the issue of whether it is reading mostly
light or dark areas of your subject. Available from most camera stores and
suppliers, a gray card is usually an 81⁄2" x 11" or smaller piece of cardboard
colored middle gray on one side.
Since light meters read for middle gray, a reading based on a gray card should
give you accurate exposure every time. To use a gray card, place it in front of
the subject, aimed toward the camera. Take the meter reading from the card
only; make sure you don’t read light from the area around the card and that
you don’t cast a shadow on the card while taking the reading. There’s no need
to focus.
Gray cards are most useful when you’re photographing still-life arrangements,
formal portraits, and other stationary subjects. You’ll need enough time
to approach the subject, position the card, and take the meter reading.
After you take your meter reading, step back from the card and compose
your subject. In manual mode, set the f-stop and shutter speed on the camera,
as recommended by the meter. In any autoexposure mode, you must use the
autoexposure lock to prevent the f-stop and shutter speed from changing when
you move the card away from the subject to take the picture.
Thus, if the meter suggests settings of f/8 at 1/125 when pointed at the gray
card, use this combination when you take the picture even if the meter suggests,
say, f/4 at 1/125 for the same scene without the gray card.
Take an incident-light reading. Almost all meters measure reflected light—the
light bouncing from the subject—and for this reason they are sometimes called
reflected-light meters. But many handheld meters also can measure incident
light, light as it falls on the subject.
Used correctly, both types of metering will suggest the same combination of
f-stop and shutter speed, even though their reading methods differ. An incident
reading is more generalized than a reflected-light reading; it doesn’t measure
specific areas of the scene, so it can’t be fooled by areas that are mostly light or
dark. In this regard, it’s like using a gray card.
To measure incident light, the meter generally has a dome or diffusing panel
over its light sensor. Position the meter at the subject and point the dome or
panel back toward the camera, allowing the meter to read the light that falls on
the subject. Use manual exposure mode on your camera and take the picture
using the meter-recommended f-stop and shutter speed, ignoring the suggested
settings of the camera’s TTL meter. If the incident meter suggests settings of
f/11 at 1/250, use this combination even if a reflected reading suggests f/8 at
1/250 or some other combination.
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