Lessons from the Shot: Workings of ISO by George Hsia

By George Hsia, www.georgehsia.com
Figure 1
When adjusting the ISO on digital cameras, one must be aware of the trade offs.
ISO – Is an indicator or rating for the sensitivity of film to light. This sensitivity is also used for digital cameras. The lower the sensitivity (ISO 50, 100) the higher the quality of photos.  The higher the sensitivity (ISO 400, 1600, etc.) the more noise or grain that is introduced into the photo, the lower the quality of the overall photo. (See Fig 1) Note the noise or grain in the ISO 1600 image.
Lower ISO settings require more light. Higher ISO settings require less light. In digital cameras increasing ISO is like turning up the amplifier on a stereo system. Like an increase in amplification for a weak signal on a stereo, High ISO boosts its signal sensitive for low light.
The ISO is expressed as sensitivity to light. The lower the ISO, the less sensitive; the higher the ISO, the more sensitive. The more sensitive the ISO, a high shutter speed could be used to get a good exposure (at the expense of image quality).  Aperture and shutter speed controls the amount of light going into the camera.  ISO is the camera’s reaction to the light that is passed through.