76 PART 2 HOW DIGITAL CAMERAS CAPTURE IMAGES
How Digital Photographers Remain
Masters of Their Domains
Despite the sophistication and the artificial intelligence found in digi-
tal cameras, there still are circumstances when the photographer must
assert the human capacity to understand things that even today’s
intelligent machines do not. Digital features let photographers give a
nudge-nudge to their cameras’ very best judgments, and the prospect
of taking a badly exposed photo shrinks to nonexistence.
For exposure, the nudge is called bracketing. And it puts the ele-
ment of chance back amid the precision of modern cameras.
How Bracketing Gives Digital
Photographers Insurance
How Photographers Use Exposure
Compensation
The photographer sets the bracketing feature on one of the
camera’s menus. Typically, the menu gives the photographer
two types of choices for bracketing. One tells the camera how
many pictures to take each time the photographer presses the
shutter button. The minimum number is an additional shot on
either side of the “official” exposure determined by the light
meter readings.The second choice is how much each of those extra exposures
should vary from the original settings. Some cameras permit
overexposures and underexposures as small as a third of a
stop, which lets a third more or a third less light reach the
image sensor. The maximum compensation per bracket is usu-
ally one stop, which doubles or halves the light. Within a range
of one stop above and below a camera’s reading, a photogra-
pher is almost always certain to find the perfect exposure.2
1
1 If you recall a few pages back in “How Light Meters See the
World,” a camera’s exposure system averages all the light
values coming from different sources: a blue cloudless sky,
long purple afternoon shadows, and pink blossoms pushing
through deep green leaves. After it has averaged all that,
the camera’s system assigns a value of middle gray—actu-
ally an 18% gray—to that average and sets the exposure
for that value only. For the average outdoor scene, the result
works well.In both photographs of the seal, the snow and the animal’s
white coat practically fill the frame. An exposure system sees
nearly pure white as the average light value in the scene
and, as shown in the simulation above, underexposes the
shot so all that white gets only enough light to turn it into
middle gray, which makes for a dirty seal and dirty snow.
Just the opposite—a black cat on a black couch—would trig-
ger an overexposure and result in a murky, washed out kitty.2