Photography Essentials Course
Chapter 3

Lesson 1: What is ISO?

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ISO

ISO in photography refers to the sensitivity of your camera’s sensor to light. The term comes from the International Organization for Standardization, which sets the industry standard for measuring sensitivity to light.

In the past, ISO was used to describe film sensitivity, but in modern digital cameras, it denotes the sensor's sensitivity to light.
A low ISO setting, such as ISO 100, is less sensitive to light and is ideal for brightly lit conditions. On the contrary, a high ISO setting, like ISO 1600 or higher, makes the sensor more receptive to light and is suitable for low-light environments. However, higher ISO settings can introduce digital noise, which deteriorates image quality.


Photographers adjust ISO based on lighting conditions and the desired shutter speed and aperture settings for a particular shot (We talk about this later on). Understanding how ISO works is crucial for achieving well-exposed and sharp photographs in various shooting conditions.

  • Auto ISO is when the camera decides the ISO for what it perceives as a ‘perfectly’ exposed picture.

    It can allow the photographer to concentrate on other settings like aperture and/or shutter speed.

    Modern cameras handle extremely well at high ISO values so the Auto ISO setting is becoming increasingly popular. One drawback would be it limits the amount of creative control you have over your image.