What is ISO?

You are probably reading it wrong! Its pronounced as 'AYE-SO'. International Organization for Standardization has defined the sensitivity of a camera sensor as ISO 100, ISO 200, ISO 400 and so on.

There are a few exceptions depending on the type of photography we do. Let's say that we are capturing a flying bird by using ISO 200 and 1/250 shutter speed. The wings of the bird will appear blurry due to motion blur. So, we have to increase the shutter speed to say, 1/2000. Now the image will be darker as ISO is 200. In order to get a perfectly exposed image, we have to increase the light sensitivity to 800 or more.

Great photography is about depth of feeling, not depth of field. Peter Adams

When boosting the ISO, the image becomes brighter. ISO helps to get a brighter image in dull light. Lower the ISO, darker will be the image. Higher the ISO, brighter will be the image. Aperture and shutter speed need to be adjusted while improving ISO settings. Shutter speed must be pushed in the opposite direction as that to the ISO.

When we don't have the luxury of ambient light, we increase the ISO limit beyond the normal range. This leads to increased grain and noise. Always keep in mind that amplifying the light information for the sensor may hamper the image quality. Even at base ISO, there is a minimum amount of noise or grain in the image.

Aperture, Shutter Speed and ISO also play an important part in getting a sharp image or a blurry one.