ISO (International Organization for Standardization) is one of the three elements that make up the exposure triangle. The other two are shutter speed and aperture. In film photography, it measures how sensitive the film is to light and in digital photography, ISO measures the sensitivity of the camera sensor to the light. Adjusting the ISO greatly affects the fineness of the image since it direct impacts how much film grain or image noise will be visible.
The principles of ISO are the same for both film and digital photography. ISO is measured with the numbers 80, 100, 200, 400 and so on. Some high-end cameras feature numbers as high as ISO 3200. When you lessen the ISO number, the grain or noise becomes less visible. This makes the image look finer and have a better image quality. The higher the ISO number, the more sensitive the camera is to the light and the more obvious the image noise. This makes the image appear grainy and it loses some of its quality. Graininess is not necessarily a bad thing especially if you're using it deliberately to create a mood. In this case, a very high ISO would be ideal.
Just like shutter speed and aperture, ISO is adjusted depending on the available light. ISO 100 is an ideal setting because your images retain their fineness and crispness. However, in low light conditions, you might need to maintain a fast shutter speed or a small aperture in which case you might be forced to increase the ISO settings in order to capture more light. The result is a better lighted image but the repercussion is a more grainy effect.
The common low light situations are indoor birthday parties, indoor sporting events or games, and night scenes. There are places which do not allow you to use flash such as galleries or theatres so to compensate for inadequate lighting, a higher ISO might be used.
A lot of beginner photographers use Auto mode, which does the job of automatically selecting the ISO settings based on the scene. It is advisable that you use Manual mode whenever possible so you can practice adjusting the exposure settings. You will then have more control over the outcome of the image.
Tags: exposure triangle, photo ISO tips, photography exposure tips, photography tip