Exposure and the Exposure Triangle

Exposure

Overexposure: the recorded image or video appears too bright, and details may be "blown out" in a wash of white light.

Overexposed images may look too bright because they were captured with settings that allow too much light into the sensor: 

• ISO may be set too high
• f-stop may be set too low
• Shutter speed may be set too low

Underexposure: the recorded image or video appears too dark, and details may be hidden or lost in artificially deep shadows.

Underexposed images may look too dark because they were captured with settings that allow less than expected light into the sensor:

• ISO may be set too low
• f-stop may be set too high
• Shutter speed may be set too high

The Exposure Triangle

As you can see, there is a three-way relationship between these three important settings:

• ISO - how sensitive the light sensor will be to light
• f-stop/aperture - how much light is allowed to pass through the lens iris
• Shutter speed - how long the shutter is left open before it closes to cut off incoming light

An adjustment to any one of these settings will impact the final exposure of the image. It is up to the photographer/videographer to set all three in balance, to achieve the desired depth of field, motion blur, exposure, and aesthetic look.