The ISO setting on a camera changes the sensitivity of the sensor. It is equivalent to film speed in analogue cameras. A low ISO setting requires a lot of light to get the correct exposure and is useful for shooting in bright conditions like a beach on a sunny day. A high ISO setting requires very little light to get the correct exposure and is useful for low light situations where you can’t use a flash, like inside a church. A high ISO setting comes at a price though, as it degrades the image quality. Firstly it creates a lot of noise, giving the photo a grainy feel. Secondly it looses colour information, resulting in a low contrast image.