Exposure is the amount of light that reaches the camera sensor. Too much light and the image is overexposed, washed out and white. Too little and it is underexposed, dark and muddy. Just right and the image has detail in the shadows, the midtones, and the highlights. Exposure is controlled by three variables: aperture, shutter speed, and ISO. Together they form the exposure triangle.

Each variable affects the image differently. Aperture controls depth of field. Shutter speed controls motion blur. ISO controls noise. Changing one requires adjusting another to keep the exposure the same. This is called reciprocity. Open the aperture by one stop and you can halve the shutter speed or double the ISO. The camera's meter measures the light and suggests settings, but the photographer decides. Expose for the shadows or the highlights, depending on what matters. There is no single correct exposure. There is only the exposure that serves the image.

The exposure triangle

• Aperture. Controls light and depth of field.
• Shutter speed. Controls light and motion.
• ISO. Controls sensitivity and noise.

Exposure is not just a technical setting. It is a creative decision. Bright and airy or dark and moody, the choice is yours.