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Canon EOS 40D Guide to Digital Photography by David D. Busch

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Dealing with Noise

Image noise is that random grainy effect that some like to use as a visual effect, but which, most of the time, is objectionable because it robs your image of detail even as it adds that “interesting” texture. Noise is caused by two different phenomena: high ISO settings and long exposures.

High ISO noise commonly appears when you raise your camera’s sensitivity setting above ISO 400. With Canon cameras, which are renown for their good ISO noise characteristics, noise may become visible at ISO 800, and is usually fairly noticeable at ISO 1,600. At ISO 3,200 noise is usually quite bothersome, which is why that lofty sensitivity rating is disabled by default and must be activated with ISO expansion using Custom Function 08. This ...

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