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Canon® EOS Rebel XSi/450D Guide to Digital SLR Photography by David D. Busch

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Program Mode

Program mode (P) uses the XSi’s built-in smarts to select the correct f/stop and shutter speed using a database of picture information that tells it which combination of shutter speed and aperture will work best for a particular photo. If the correct exposure cannot be achieved at the current ISO setting, the shutter speed indicator in the viewfinder will blink 30 or 4000, indicating under- or overexposure (respectively). You can then boost or reduce the ISO to increase or decrease sensitivity.

The XSi’s recommended exposure can be overridden if you want. Use the EV setting feature (described later, because it also applies to Tv and Av modes) to add or subtract exposure from the metered value. And, as I mentioned earlier in this ...

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