In this Photography 101 article, you will get to know more about the famous Sunny-16 Rule. This is an empirical rule that was invented to guesstimate which camera settings to use for a balanced exposure when shooting outdoors during sunny days.
Sunny-16 Rule in the Digital Era
The Sunny-16 rule was a must have in a film photographer’s bag of tricks, but nowadays, in the digital photography world, built-in light meters are present in every device, from the cheaper cameraphone to the pro-graded DSLR camera.
Nonetheless, the Sunny-16 Rule can still serve you well in several ways:
It’s a useful exercise to improve your ability to read the available light. With a light meter app on you smartphone, you do not need to take any picture at all. Just check the settings you would use against those suggested by the app.
I like to use the app Pocket Light Meter on my iPhone to keep practicing my ability to reading light. Here, I bet on the Sunny-16 and was right.
It makes it easier to experiment with film photography, for example, when shooting large format 6×6 film;
Yashica LM-MAT TLR 6×6 medium format film camera.
It makes you work faster in manual with your digital camera by sparing you the trial and error process to get your settings right.
What Does the Rule Say
The rule simply states that, on sunny days, at an aperture of f/16, your shutter speed is the inverse of your ISO value.
This means that if you are at, say, f/16 and ISO 100, your shutter speed should be 1/100 seconds.
This is a good example of light conditions that match the prediction of the Sunny-16 rule.
The Exposure Triangle
The rule works on the so called exposure triangle. Your image exposure is the result of the combination of aperture, shutter speed and ISO values. The triangle works on the assumption that you can obtain the same exposure by properly changing those values.
The Exposure Triangle. Shutter Speed, Aperture and ISO works together to determine the image exposure.
For example, if you are using f/16, ISO 100 and shutter speed of 1/100s, the same exposure is also obtained with the following settings combinations:
f/11 (+1EV), ISO 100 (0EV) and 1/200s (-1EV)
f/16 (0EV), ISO 200 (+1EV) and 1/50s (-1EV)
Note that here we are discussing only the image exposure, while not considering other aspects that could differ from one setting combination to the other, such as image noise and depth of field.
The over- or under-exposure with respect to the original settings are reported in the brackets.
It is good practice to familiarise yourself with the exposure triangle and the settings equivalences that derive from it, in particular if you are shooting with mirrorless and compact cameras.
Not all cameras and lenses allow you to shoot at f/16 or narrower apertures. For example, my Sony RX100 does not close more than f/11, while after f/8, micro four thirds cameras may start to suffer from diffraction.
As you may know, it is not always sunny out there. Some days are pretty dark and the sunny-16 rule does not fit those conditions very well. For this reason, there are different rules depending on the weather.
Those rules are named in a rather self-explanatory way: Slightly Overcast-11, Overcast-8, Heavy Overcast-5.6, Sunset-4 and Snowy-22 (for sunny days and snowy terrain).
The image below illustrates the conditions for which the different rules apply:
Snowy-22: If the sun is shining over a snowy landscape, f/22 is the suggested aperture so that a balanced exposure is achieved using a shutter speed that is the inverse of your ISO;
Sunny-16: when photographing in an open field during a sunny day;
Slight Overcast-11: when the sky is variable;
Overcast-8: cloudy weather, but not really dark;
Heavy Overcast -5.6: bad weather, may be rainy;
Sunset-4: for typical sunset conditions.
The principle is the same as for the Sunny 16. In overcast conditions, the Overcast-8 Rule says that to achieve a shutter speed of 1/100s you should set your camera to f/8 and ISO 100.
Let’s see a couple of examples:
A classic light that suits the Overcast-8 Rule better than the Sunny-16.
This is a typical situation for the Heavy Overcast-5.6 rule.
Forget the Weather, Read the Shadows
To guesstimate which rule best matches the light conditions, it is better to look at shadow hardness, rather than actual sky conditions.
In this photo, the sky looks great and clear, but some clouds are blocking the sun. As you can see, there are no shadows on the ground.
In these conditions, the light meter of my Sony RX100 Mk II tells me that a balanced exposure is obtained at ISO 100, f/11 and shutter speed of 1/100s.
This is the Slightly Overcast-11 rule.
While the sky suggests the Sunny-16 rule should apply, because of passing clouds in front of the sun, the in-camera light meter will tell you that the Slightly Overcast f-11 rule works better.
With very soft shadows or no shadows at all, you want to use the Heavy Overcast-5.6 rule, while the Sunny-16 works best with hard, deep shadows. Anything in-between is for the Overcast-8 or Slightly Overcast-11 .
One of the best use of these rules is by applying them you will get fluent in reading light and shadows hardness.
The Sunny-16 Rule in Real Life
These rules are empirical and not exact, nor are they rigorous. Reality is not made of individual factors (sun, clouds, heavy clouds, etc.) but is an ever changing mix of different factors and there are no bulletproof rules.
This is why it’s important to know how to read the light, particularly for an outdoor photographer.
Let’s consider the image below.
This image will defy the Sunny-16 rule
You can see very strong shadows on the ground, but the in-camera light meter is telling me that to have a shutter speed that is the inverse of my ISO (i.e., 1/100s) I should use an aperture of f/5.6, and not f/16 as the hardness of the shadows would suggest.
Why? because the scene, due to the strong foliage, is, in average, rather dark compared to the brightness of the image below, taken only a few minutes later and under the same kind of daylight.
This image of an open ground, instead, follows the Sunny-16 rule. In general, open ground images are much brighter than those taken under the canopy of trees or with large portion in the shadow. For those the use of these empirical rules is not that straightforward.
And if this isn’t enough to convince you to use the Sunny 16 rule, check out this video of astronaut Chris Hadfield using this rule when taking pictures of Earth from Space!
While the modern digital photographer does not need to memorise those rules, thanks to the in-camera light meter, practising with the sunny-16 rule (and the other similar ones) is a great exercise to learn to read the available light, a must for any outdoor photographer.
And you can start practising right away! Take a look out the window: is that sunny-16 weather or something else?
A note from Josh, ExpertPhotography's Photographer-In-Chief:
Thank you for reading...
CLICK HERE if you want to capture breathtaking images, without the frustration of a complicated camera.
It's my training video that will walk you how to use your camera's functions in just 10 minutes - for free!
I also offer video courses and ebooks covering the following subjects: