Understanding ISO

Before digital photography, ISO signified the sensitivity of chemical films. A film with a higher ISO rating has larger photosensitive crystals that are more sensitive to light. Many useful best practices evolved around this fact, incorporating what is called the exposure triangle: exposure time, lens aperture and ISO. These are used to determine the optimal camera settings to get a properly exposed image. Increase the ISO and you can decrease the exposure time or reduce the aperture.

The whole world of photography once revolved around the exposure triangle, and millions of people captured excellent images under many different lighting conditions thanks to a thorough understanding of the relationship among ISO, aperture and exposure time.