The Canon EOS Digital Rebel XSi/450D Companion

PROGRAM MODE

WHITE BALANCE

125

A Real-World ISO Change

Let’s say you’re trying to shoot a close-up of a flower on a windy day. Your meter

has recommended 1/125th of a second at f3.5. is is great because it gives you

the shallow depth of field that you want, but it’s so windy that 1/125th of a sec-

ond is resulting in an image that’s too blurry. If you increase the shutter speed

by two stops to 1/1000, the image will be underexposed, because the camera’s

aperture can’t be opened any further.

But, if you increase the ISO from 100 to 400 (a two-stop difference), you’ll have

enough exposure latitude to make your shutter speed change and get your shot.

White Balance

While your Rebel XSi is an incredibly sophisticated imaging instrument, it still

pales in comparison to the human eye. Your eye has better autofocus, can per-

ceive a much wider range of tones and colors, and has the amazing ability to

autocorrect color under different types of light.

at last one may not sound that difficult, but think for a moment about your

street corner. During the daytime, it’s covered with sunshine (unless it’s a cloudy

day), but at night, it’s lit up by a street light. e street light is very yellow, while

sunshine is much “cooler”—closer to the blue end of the spectrum - and cloudy

light cooler still.

Similarly, the light you’re sitting in right now might be an entirely different color.

It will vary ...