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Old Sep 26, 2007, 9:24 AM   #1
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Hi, I'm new here so if I'm posting this in the wrong forum, please forgive me. I'm not trying to make a buying decision as I have already made my purchase, I'm just curious to understand something.

Can someone explain to me why the Canon PowerShot S5 IS (a "prosumer" class camera) would have a physically smaller CCD (1/2.5 inch) than the PowerShot A series cameras? (A630 is same megapixel as the S5 but the CCD is 1/1.8 inch as are all of the CCD's for the A series)

As I understand it, a physically larger CCD captures light better and makes a better picture. On the other hand, the S series is supposed to be a higher end class of camera. It doesn't seem to make sense that Canon would put a lower end CCD imager into the higher end camera, does it?

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Old Sep 26, 2007, 10:48 AM   #2
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The larger the size of the photosites, the better the image quality as ISO speeds are increased, all else being equal. That's because you have more surface area for each pixel for gathering light and less amplfication is required for equivalent sensitivity).

But, all is not equal between sensors, since improvements are being made with each new generation. So, you really need to take each sensor on a case by case basis. Ditto for the camera (even when more than one model is using the same sensor), since you can have big differences in the image processing algorithms being used.

One reason a smaller sensor is used in the Ultra Zoom type cameras is to keep the size and weight down. A much smaller lens design for the same angle of view and brightness can be used with a smaller sensor.

That's because the actual focal length of the lens can be much shorter to get the same angle of view you'd need a higher focal length lens for on a 35mm camera.

For example, the actual focal range of the lens on the S5 IS is only 6-72mm (you'll see that stamped on the front of it's lens), even though you get the same angle of view (apparent magnification) that you'd need a 36-432mm lens for on a 35mm camera model.

The size. weight and cost would increase if a larger sensor was used to get the same apparent magnfication and brightness.

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