ISO settings
On all compact digital cameras and digital SLR ISO settings can either be manualy set or automatically set by the camera. An ISO setting dictates how sensitive to light the digital sensor should be. The sensor in the camer captures the detail of the image, the data is then turned into digital signals to be stored on a memory card. ISO settings start at around 50 and generally go up to ISO 400, some dslr cameras can go up to 3200. The higher the ISO number the more sensitive the sensor is and will take in more light. Taking a photo out side in bright sun light would mean a low ISO setting maybe of 100 or less. Taking a picture in doors at a party would need at least a 400.
AUTO ISO
The camera decides on the settings, by judging the brightness of the settings. The photographer has no control.
ISO 50 - 100
This manual setting is best used for images taken in bright sun light, portrait and landscape photography. It can be used for macro photography as it also tends to produce better quality
ISO 100
Adds extra light to the image with out any loss in quality, a good use for photography in the shade on a sunny day.
ISO 200
Best used on cloudy and overcast days. Acceptable image quality, though loss in the over all quality of the picture can be detected.
ISO 400 and above
For use when you are unable to use a flash. Also useful for indoor photography whether you use a flash or not. If you intend to take action photos like sports then a high ISO setting with a quick shutter speed will be needed to ensure that you capture the action quickly with enough light.
http://www.print-digital.info/articles/digital-camera-sensitivity.html
