ISO (short for International Organization for Standardization) is an international standard-setting organization. It develops international standards for many aspects of daily life. Prior to the establishment of the ISO, national abbreviations such as DIN (Deutsches Institut für Normung / German Institute for Standardization) or ASA (American Standards Association) were used.
In photography, ISO-values stand for the light sensitivity of the recording medium. The value indicates the sensitivity of the image sensor of a digital camera. ISO-value stands for the film speed when talking about film in analogue photography. While analogue photographers have to choose a specific ISO-value before photographing (since changing the film role continuously would be a pain), digital cameras provide photographers with the possibility of changing the settings in the camera menu with ease.
The lower the ISO-value is, the lower the light sensitivity of the image sensor. By default, ISO values between 100-200 are used. With a doubling of the ISO-value, the necessary exposure time is halved since the image sensor records the same amount of light in half the time. This doubles the shutter speed, which often leads to blurry images. This can be avoided by changing the ISO setting.
Different ISO-values work best in various situations. Even recommendations camera manufacturers give to their customers can be very different from brand to brand.
ISO 50 – 200: Photographing outdoors with adequate lighting, e.g. on a sunny day
ISO 400 – 800: Photographing on cloudy days, in the evening, or indoors with good lighting
ISO 800+: Photographing at night or indoors with poor lighting
A disadvantage of increasing the ISO-value is the appearance of negative effects (so-called image noise). How pronounced these are in the image heavily depends on the type and size of the camera’s sensor. This effect happens much more often when using a compact camera with a smaller image sensor. Image noise comes about because raising the ISO-value requires an amplification of the signals from the sensor. When this occurs, not only the light signals are amplified, but also the interference in the image. These interferences are mostly visible in dark surfaces. On the borders in the image, there is often a significant loss of detail.
In order to take attractive photos, it’s important to select a good combination of ISO-value, aperture, and shutter speed. When in doubt, it’s better to use a tripod and increase the shutter speed instead of raising the ISO value and thus risking the appearance of more image noise.