A “rule of thumb” used in photography, the Sunny 16 rule helps photographers determine proper exposure settings in bright sunlight without using a light meter. This method suggests that an aperture of f/16, combined with a shutter speed reciprocal to the ISO film speed (or ISO setting for digital cameras), will produce a well-exposed image under these conditions. For example, with an ISO of 100, a shutter speed of 1/100th of a second at f/16 should result in a correct exposure. Variations exist for different lighting conditions, offering starting points for cloudy, overcast, or shaded scenarios. Applications or tools that assist in applying this rule can simplify exposure calculations.
This principle empowers photographers to understand the relationship between aperture, shutter speed, and ISO, fostering a deeper understanding of exposure control beyond automated settings. It remains valuable in situations where light meters are unavailable or impractical, and contributes to quicker decision-making in dynamic lighting conditions. Developed before the prevalence of built-in light meters, it continues to serve as a practical educational tool for comprehending photographic exposure and its underlying mechanics.
