The international standard measurement of a camera’s sensitivity to light, is called it’s ISO. For analog film cameras, the ISO is the “film speed,” which is based on the chemical composition of the film. Changing ISO means loading a film with a different speed.
However, ISO also exists on digital cameras. ISO indicates your digital camera’s sensitivity to light. The higher the number, the less light is needed to take a photo that is correctly exposed (not too dark or too light).
In bright light (like the middle of a sunny day), you’ll normally use ISO 50 or ISO 100. These lowest settings can be used because there is lots of light around.
In lower light, your camera needs help. Two ways of doing this are:
1)Decrease Shutter Speed.
With a slower shutter speed, the camera has more time to ‘take in’ the amount of light it needs. Unfortunately though, the slower the shutter speed, the more chance that your images will turn out blurry.
Rather than decrease the shutter speed, you can increase the ISO.This will increase the sensitivity of the camera which means you can get the same shot with less light entering the camera. Thus the shutter speed can be kept low enough to avoid blurry images.
As increasing the ISO will increase the shutter speed, a high ISO will also help when taking fast moving sports shots. You’ll get clear, crisp shots with no blur.
However it is still recommended that you use the lowest possible ISO.
This is because there are a lot of problems that come with High ISO.
Using a higher ISO means the camera has less light to work with. Unfortunately this also means that ‘noise’ is introduced into your camera, so your images will be grainy.
Your camera’s highest ISO value will produce a lot of noise in your image, so it is best not to use it unless there is barely any light and it is essential. It is better to choose the second highest ISO.
Most cameras have an “Auto ISO” setting. With Auto ISO, the camera will look at the amount of light in the scene and change the ISO appropriately so that the shutter speed doesn’t get too slow.