The Sunny f/16 Rule for Digital Exposure
The sunny f/16 rule, or Basic Daylight Exposure (BDE for short), tells you that the proper exposure in digital photography for a frontlit subject is f/16 with a shutter speed of 1/ISO (that’s 1 over the ISO in use). According to the sunny f/16 rule, at ISO 100, BDE would be f/16 at 1/100 second, and at ISO 200, BDE would be f/16 at 1/200 second.
When taking photos on a bright, sunny day, set the ISO of your camera to 100, the aperture to f/16, and the shutter to 1/100 second. Then go out and take pictures of some frontlit subjects. As long as your subject isn’t white or black, the exposures should be great. No metering necessary.
You can use equivalent exposures (different combinations of apertures, shutter speeds, and ISO settings that provide exactly the same exposure) for the sunny f/16 rule. The following table shows the equivalent exposures for the sunny f/16 rule at ISO 100.