Fundamentals
Understanding ISO: The Third Pillar of Exposure
You’ve learned about aperture and shutter speed. ISO is the third variable in the exposure triangle, and it’s the one most photographers understand least clearly. Let’s fix that. What ISO Actually Does ISO controls your camera sensor’s sensitivity to light. A higher ISO number means the sensor amplifies the signal more, making the image brighter. A lower ISO number means less amplification, producing a darker image from the same amount of light.