Setting the ISO
By setting the ISO you are are taking control of how sensitive the sensor in your camera is to light. It may not sound like much but this is the first real step toward taking full control of your camera. Setting the ISO is as easy as choosing a number in the ISO settings menu. Which number you should choose has to do with the amount of light available to make images.
As a rule of thumb 100 – 200 ISO is good for outdoors while 400 – 800 ISO is generally good for indoors. You should use the lowest possible ISO that allows you to make the image you want under the lighting conditions you have.
To make things a little easier for this discussion lets say the ISO range for your camera is from 100 to 3200 ISO. Check your camera’s owner’s manuel for the ISO range of your camera. The options you will see in the ISO settings menu (other than Auto) will be: 100, 200, 400, 800, 1600, 3200. Notice that as the numbers increase they double. This is because with each higher number the camera’s sensor is twice as sensitive to light as was with the number before it. For example, when the ISO setting is changed from 200 to 400 the sensor needs half as much light as it needed at 200 ISO.