What is ISO in digital photography?

An ISO in digital photography refers to the sensitivity of the image sensor. A high ISO means the image sensor is very sensitive to light thus enabling you to freeze a moving object while a low ISO enables you to capture a blurring object due to low sensitivity of the image sensor. A high ISO also contributes to the graininess of the image as shown on the image below.

Not necessarily graininess in the photo means a bad image quality as graininess achieved by high ISO can used to create an effect on the image. Depending on what you want to vary your ISO, you should consider the following question:

1. Is the object moving?
2. Is the place poorly lit?
3. Am I going to achieve a graininess effect on my image?

If the object is moving and you don't have enough shutter speed to freeze the object, it is best to increase ISO to gain more shutter speed. Likewise, if you wan to blur the object, a lower ISO is feasible.

Under a poorly lit environment, it is very hard to take a picture without risking camera shake. As such it will be good to increase ISO. If you have a tripod or any other objects that can stabilize the camera, then you can mount your camera on top of the tripod or place on the object without achieving graininess in the picture.

If you want to have graininess in your image, you can set to high ISO to achieve the effect that you want.

In short, whether you want to vary your ISO depend very much on what you want to achieve and the following questions mentioned above served as guidelines to help you.

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