Some people are used to having a light meter tell them what aperture they should use. In bright daylight, sunny f-16 rulephotographers usually employ light meters in order to get the correct aperture setting. This can mean the difference between a photograph that is overexposed or underexposed. Therefore, these things are invaluable to the photographer. But what if there comes a time that a light meter is not available to the photographer? What then? The solution to that problem is for the photographer to employ the Sunny f/16 rule.

The Sunny 16 rule or most often called the "Sunny f/16 rule" is a rule that is used to efficiently come up with the proper daylight exposures without using a light meter. The essential steps to getting a correct daylight exposure without having to use a light meter is to set the aperture to f/16 and the shutter speed to the ISO speed. One example would be to set the aperture to f/16, choose ISO 100 as your film and then have your shutter speed as 1/100 seconds or maybe 1/125 seconds.

A more elaborate setting for the Sunny f/16 rule is to first set the shutter speed to the setting nearest to the ISO film speed and then set the aperture value (f-number) according to the daylight settings. For example, if the lighting condition is sunny, then you will set your f-number to f/16. You could also remember this setting if the shadow detail that you see on your subjects are quite distinct.

If the lighting condition is slightly overcast and the shadow detail is quite soft around the edges, you should set your aperture to f/11. If the lighting condition that you have when shooting is overcast and the shadows are barely visible, then you should set your aperture value to f/8. And finally, if the lighting condition outside is heavy overcast and there are no visible shadows being cast, then you should set your aperture value to f/5.6

These are the most common settings that have been the standard by other photographers since day one. It is important to note that these settings have been set in order to help the photographer gain the best and most even exposure distribution across his or her photograph. If there will be any other particular effects that the photographer would like to include in his photographs, then it would be up to the photographer’s discretion as to what aperture to use. The final say falls on the photographer and the set aperture will always be determined by him.