The f16 or Sunny 16 rule is one of the most valuable pieces of information you will need to understand your camera and exposure. Without it, we would find ourselves in a huge standards war with different camera manufacturers claiming that they have the best standard. Learning photography would become unnecessarily complex and expensive. Just like DVDs, Blu-Ray, VHS etc., having a universal photography standard makes our lives as photographers simpler and, perhaps more importantly, much cheaper.
F16 explains ISO
Describing ISO using the f16 rule is a beginner photographer’s rite of passage. If you are able to teach another person about ISO using the f16 rule, you are officially no longer a beginner and can consider yourself promoted to knowledgeable hobbyist. Once you fully understand the f16 rule, all other factors in the exposure equation fall nicely into place.
Why is it important
Fully understanding exposure and how your camera works will open untold possibilities in photography that would otherwise be unavailable. Your technical and creative skills will improve exponentially. The f 16 rule is the key that unlocks the door to photography’s hidden garden of beauty. Understanding this will give you many years of development and personal satisfaction as a photographer.
The f 16 Rule
The f 16 or Sunny 16 Rule states that, on a bright sunny day at noon with your aperture set to f16, the reciprocal of the ISO setting is the correct shutter speed. If the ISO is set to 100, your shutter speed should be 1/100 or as near as you can get to 1/100. At ISO 200 the shutter speed should be 1/200. At ISO 400 the shutter speed should be 1/400 and so on. It is a rule that you should have locked permanently in your brain.
The ISO 2720:1974 standard applies to your camera’s exposure meter and how it measures light. The ISO standard for translating this metered light into image brightness via your camera sensor is ISO 12232:2006. This standard only applies if you save your image as a jpg. There are no ISO standards for RAW files which means that you may get considerable variation in exposure from camera to camera in RAW files shot at the same exposure settings. This also explains, in part, why, when you open a RAW file in editing software on your computer, it can look very different from the jpg that you see on the back of the camera.
(More information SEE HERE)
Same rule anywhere in the world
The f16 rule applies everywhere in the world. It is a universal constant because it relates to the intensity of light coming from the sun. If, on a clear, bright sunny day at noon, you are freezing at the top of mount Kilimanjaro or melting in Death Valley you can still rely on the f16 rule to get a good exposure. Wherever you take you camera you can be sure that the f16 rule will be your reliable standard with two notable exceptions.
Two Notable Exceptions
Because snow, sand (glass) and water reflect sunlight, the f16 rule becomes the f22 rule when the ground is covered in snow or you are at the beach. This is only because the reflected light doubles the amount of light available on your subject equating to an increase of one stop of light.
It’s a starting point
By using the f16 rule as a starting point we can work out several other exposure values even when the sun is not shining. With some experience and study you will be equipped to shoot in almost any lighting scenario without using an exposure meter.
In the scenarios shown in the chart below, the rule continues to apply. At each of the aperture settings the shutter speed should match the reciprocal of the ISO
|f/22||Layer of Snow or at The Beach, Sunny Day|
|f/16||Sunny Day at Noon|
|f/4||Open Shade / Sunset|
It Is Part Of Your Camera
The f 16 rule is designed right into your camera as part of adhering to ISO standards. Try it out the first chance you can get. Use the chart above and check your results against the same images shot using camera controlled exposure as in Aperture Priority. See if you can improve upon your very expensive and highly specified masterpiece of engineering; your camera.
Example 1 shows an overexposed flower. This is the best job that the camera can do when the flower is lit by direct sunlight and the background is in the shade. (f2.8, ISO 200, 1/2000)
Example 2 is the result of using the f 16 rule on the same flower shot. None of the colors in the flower are lost to overexposure. (f2.8, ISO 200, 1/6400)
Example 3 shows an underexposed flower where the camera meter has been fooled by the sunlight in the background. (f2.8, ISO 200, 1/4000)
Example 4 shows the same flower using the f 16 rule in the shade which is three stops darker than direct sunlight. (f2.8, ISO 200, 1/800)
Photos copyright William Benson