Quote:
Originally Posted by InsaneSkippy
ISO:
Higher the number, the more light coming in to the camera. However, if you go too high, you increase the amount of "noise" in the shot, these are small spots on the picture making it appear grainy. If you're in a low-light situation, this is your best tool, as noise can be fixed (somewhat) in post processing, where as camera shake cannot be..
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Nice link.
However, I think it's less confusing to think about ISO as the camera's sensitivity to the available light, instead of thinking about the amount of light coming into the camera, which varies with shutter and aperature, but not ISO. So a low ISO number (say 100) requires more light at a given shutter/aperture combination while a higher ISO (say 800) requires less light at the same shutter/aperture combination, but leads to a lower quality image, showing more "noise."
ISO performance, the ability to perform at high ISO's with little noise, varies greatly from camera to camera. In general, the larger the sensor and more expensive the camera, the better it's performance will be at higher ISOs. Most point and shoot cameras start showing lots of noise at ISO 400, while an entry level DSLR might do pretty well up to ISO 800 and a full frame DSLR might be good up to 3200 ISO.
The beginner will become aware of ISO performance when trying to use available light and avoid using a flash. Of course, if you're stuck without a flash and high ISO is the only way to get a shot, then go for it. Don't miss or hopelessly blur a shot because your were afraid of noise.
Dave