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Anonymous
>>211133 A 1/2.5" CCD is a standard size for a digital compact. The largest you're likely to see is 1/1.8" (they're specified this way because it's based on TV camera CCD sizes). Basically, a smaller sensor means that the light-gathering sites are smaller, and so the signal to noise ratio is worse, meaning there's more noise on the image. The smallest sensor you're likely to see on a digital SLR is about four times the size of an average compact CCD, and the highest end MF backs have sensors up to a few inches on a side. The larger sensor means more effective light gathering and so less noise. That's the main advantage.
The only really weird thing to take out of this is that, for a given CCD size and all else kept equal, the resolution in megapixels is inversely proportional to the amount of noise. A 1/2.5" CCD with 4 megapixels will have photosites about 3 times the size of those on a 10-MP CCD of the same dimensions, so it will tend to be less noisy. Don't just jump for the camera with the highest resolution, because that makes far less of a difference to the final print quality than the lens and the amount of noise in the image.
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