The Canon EOS Digital Rebel XSi/450D Companion

CHAPTER 5

EXPOSURE MECHANISMS

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So, one of your primary concerns as a photographer is to make sure that you’re

choosing settings that expose the camera’s sensor to an amount of light that will

render a scene that is neither too bright nor too dark.

Exposure Mechanisms

Your camera gives you two mechanisms for controlling the amount of light that

hits the image sensor. Using these mechanisms, you can ensure that you don’t

end up with images that are too bright or too dark.

In Chapter 2, you learned about the shutter, a curtain that opens and closes in

front of the shutter to expose it to the light that is focused through the lens. By

using a faster shutter speed, the shutter will open for less time and thus expose

the sensor to less light.

e second mechanism that the camera uses to control light is the iris or aper-

ture. is concept should be somewhat familiar because your eyes have irises in

them, and if you’ve ever walked out of a dark movie theater in the middle of the

afternoon, you know what it’s like to wait for your pupils to close down so that

your field of view ceases to be overexposed.

e iris in your camera is built from a series of interlocking leaves that, when

rotated, create an expanding or shrinking opening, or aperture. e wider the

aperture, the more light that gets let through to the sensor.

e aperture is positioned at the very end of the lens, just be