The Canon EOS Digital Rebel XSi/450D Companion

ADVANCED EXPOSURE

THE LIGHT METER REVISITED

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correct for 18 percent gray, then the odds are that its calculated metering will be

correct for your scene.

Most of the time this works. But, sometimes 18 percent gray assumption is incor-

rect. e field of white snow is a great example. Since the camera is assuming that

it’s pointed at something that’s 18 percent gray, it calculates an exposure that will

represent the field of snow as gray rather than white. Fortunately, the XSi’s meter

is so sophisticated that it will usually recognize a strong white object as white and

calculate an appropriate exposure.

Nevertheless, when subjects are bright white, you want to carefully review your

images to make sure the white doesn’t appear gray. If it does, then you’ll need to

overexpose your shot to render white objects as true white. We’ll look at how to

do this in just a bit.

Exposing So at Black Looks Black

Black objects are more likely to trip up the XSi’s meter than are white objects.

Again, if you point the camera at a black object, it will assume that the object is

actually 18 percent gray and so will concoct exposure settings that will properly

render that object as gray. Consequently, black objects can sometimes appear

ashen-looking.

Because the light meter assumes that it’s pointed at something that’s 18 percent

gray, it calculates an exposure that renders the black tone of this car so ...