This series of articles is excerpted from Rocky Nook’s Enthusiast’s Guide to Exposure by John Greengo covers the controls — shutter, aperture and ISO. The week, John talks about ISO.
What is ISO?
ISO describes the sensitivity rating of your camera’s sensor. The sensor records the light that enters through the lens, passes through the aperture opening, and moves past the shutter unit. The ISO settings can be adjusted to change the sensitivity. While the imaging sensor can work with a wide range of light levels, it will achieve maximum performance when exposed to a particular amount of light. This peak performance level is called the base or native sensitivity.
The base or native ISO setting is the lowest numbered ISO setting, most frequently ISO 100 or ISO 200. This is the setting that will result in the highest-quality signal, the lowest noise interference, and the greatest dynamic range. When set to a low ISO, the sensor receives just the right amount of light, and the resulting image is free of artifacts and noise. These qualities increase with higher ISO settings. It’s considered best practice to try to use the lowest ISO setting possible for any given situation. The primary reason for selecting a higher ISO is to compensate for a faster shutter speed. For example, if you have a shutter speed of 1/250s and you want to stop the motion of a runner, you should move up to 1/500s to freeze the action. The change of shutter speed will result in less light reaching the sensor, so you’ll need to compensate with either a larger aperture or a higher ISO setting. Increasing aperture is a good first move. If you don’t have that option, raising the ISO will solve the problem. As you increase your ISO settings, the image quality will degrade. ISO performance is influenced by the size of the sensor, the size and number of pixels the sensor has, and how the signal is processed. Newer cameras with large sensors and fewer pixels tend to do the best. Many photographers will test their cameras, checking the results at all ISO settings. As the ISO settings go up, the quality goes down. At a certain point, most find a quality “ceiling” at which point the quality level is unacceptable. For many cameras, the two highest available ISO settings are above this quality ceiling. Test your camera to see how it performs and see how high you can go before hitting your ceiling.
Background Information on ISO
ISO (International Organization for Standardization) is a worldwide independent group that develops voluntary standards. This ISO standard is for recording light. The same standard is used for film. These standards ensure that all cameras will capture a similar image if similar settings are used.
Opening photo: ©2020 Kevin Ames
Read more selections from the Enthusiast’s Guides from Rocky Nook.