Monday, December 22, 2008

Adjust Exposure Manually

The most basic manual exposure control you can exert over your camera involves setting both
the aperture and shutter speed. Some digital cameras allow you to set these controls as if you
had a fully automatic 35mm SLR. There are two kinds of cameras you may run into with this
capability:
Point-and-shoot Most point-and-shoot digicams that include manual settings for
aperture and shutter speed require you to use the LCD display to make onscreen menu
changes. The camera shown in the following illustration, for instance, uses a pair of
buttons on the right side of the LCD display to adjust shutter speed and another set of
buttons on the bottom of the screen to change the aperture settings. It isn’t hard to do,
but you need to remember to first set the camera to its Manual Exposure mode, and then
remember which buttons do what for fine-tuning the exposure.

D-SLR Some digital cameras—Digital SLRs, mainly—use traditional SLR-style
controls for making manual adjustments to exposure. Specifically, you can turn
the aperture ring on the lens to change the f/stop or use a control on the camera to
accomplish the same thing, as shown in the following illustration. Shutter speed
is likewise affected with a dial on the camera body, and you can look through the
viewfinder to keep tabs on the setting.

To set exposure manually, you must choose a shutter speed and aperture combination that
will properly expose your scene at a given ISO. This is a great exercise for new photographers
who are serious about learning photography theory.

Use the Sunny 16 Rule
At an ISO of 100, which many digital cameras use for general-purpose photography, you
might want to rely on the traditional Sunny 16 Rule for a starting point. The Sunny 16 Rule is
very old—it dates back to the earliest days of analog photography—and it suggests that when
shooting outdoors in bright sunlight, you should choose an aperture of f/16 and a shutter speed
that’s equivalent to your film speed. Since few cameras offer the ability to choose 1/100, most
photographers who rely on this rule use 1/60 or 1/125 when shooting with ISO 100 film. Here
is a chart that identifies other acceptable combinations. (All of these add up to the same overall
exposure.)
Keep in mind that these recommendations are just a starting point. Here are some tips that
can help you zero in on your ideal exposure:
■ Your camera will often recommend an ideal exposure, which you can accept or reject.
If the camera considers your setting out of bounds, it may flash a warning in your
viewfinder.
■ Adjust your exposure based on the ISO setting. If your camera is set to an equivalent
of ISO 200, for instance, the Sunny 16 Rule would call for a shutter speed of f/16 and a
shutter speed of 1/250.
■ Make adjustments for brighter or darker scenes. If you’re shooting in a dark room, for
instance, the Sunny 16 Rule doesn’t really apply—but it’s a good starting point. Open the
aperture or lengthen the shutter speed to account for reduced light; close the aperture or
shorten the shutter speed to account for increased light.

Use Shutter or Aperture Priority Adjustments
Instead of relying on an all-automatic or all-manual exposure system, you can compromise and
use your camera’s shutter or aperture bias, if it has one. The idea with these controls is that you
select either an aperture or a shutter speed, and the camera automatically selects the other half of the exposure for you.
Aperture and shutter priority modes are discussed in more detail in the section “Use Your
Camera’s Various Exposure Modes.” These settings are usually used to find the right balance
between freezing (or blurring) motion in a picture and focusing attention on the subject by
sharpening (or blurring) the background of an image.

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