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The Sunny Sixteen Rule

Shooting a few rolls of medium format film using an old Bronica ETRS, a camera that has no internal light metering, made me stop and think about the way I make photographs. The heart of photography is the study of light. The Sunny 16 Rule is a good starting point.

The Exposure Triangle (a Conceptual Model)

To better understand the exposure to light when you’re making photographs it helps to consider the ‘conceptual model’ of the Exposure Triangle. The three considerations to make in relation to each other are the ISO (sensitivity of the film or sensor), the Shutter Speed (how long the shutter remains open) and the Aperture (the size of the hole in the lens). A combination of these three elements of the triangle result in the exposure of the photograph.

In clear English, compromises are made in the amount of light you want to reach the film or sensor depending on the size of the hole and the amount of time the hole remains open.

Understanding the Concept of Aperture Fstops

Fortunately cameras have a logical way of dealing with the changes for Aperture and Shutter Speed – called Stops. The Aperture (size of the hole in the lens when the photograph is made) operates by fstops. The larger the Aperture means the smaller the fstop. While the smaller the Aperture means the larger the fstop. So as you move into lower light situations where your exposure requires the Aperture hole to be wider open then you need to adjust the fstop value downward.

An fstop downward doubles the size of the Aperture hole in the lens and an fstop upward halves the size of the Aperture hole in the lens. The full fstops are:

f/1 – f/1.4 – f/2 – f/2.8 – f/4 – f/5.6 – f/8 – f/11 – f/16 – f/22 – f/32 – f/45

Note: The first and second number are doubled through that fstop increment so that f/1 becomes f/2 becomes f/4 and f/1.4 becomes f/2.8 becomes f/5.6. Your camera may provide half or third stop increments so it’s important to remember these full fstop values.

Understanding the Concept of Shutter Speed Stops

The idea of Shutter Speed stops is a lot more intuitive. The lower the Shutter Speed stop number means a longer time the shutter remains open. The result of slower shutter speeds can be blur from either shake or subject motion. Fast shutter speeds have the opposite effect and freeze motion in its tracks. The shutter speed you want will be dictated by the available light, the subject being photographed and compromises in the Exposure Triangle (ISO, Shutter Speed and Aperture). Full shutter speed stops range from seconds at the slow end up to thousandths-of-a-second at the fast end.

30 – 15 – 8 – 4 – 2 – 1 seconds… followed by 1/2 – 1/4 – 1/8 – 1/15 – 1/30 – 1/60 – 1/125 – 1/250 – 1/500 – 1/1000 – 1/2000 – 1/4000 – 1/8000 fractional seconds.

An increase of the Shutter Speed by one stop halves the amount of light to hit the film or sensor because the faster shutter allows less light through. A decrease of the Shutter Speed by one stop doubles the amount of light to hit the film or sensor because the slower shutter speed allows more light through. So the idea is to slow down Shutter Speed as light becomes less available. All things being equal, a sunny and bright day allows you to use a faster shutter speed than if the photograph is being made on a cloudy dim day.

As with Aperture fstops, your camera may offer 1/2, 1/3 or 1/4 stop increments for Shutter Speed.

Shooting without a Meter using the Sunny 16 Rule

The Sunny 16 Rule used to be on the inside of film boxes and it may not replace your fancy light meter but it’ll get you close to the right exposure in a pinch. The Sunny 16 Rule is that on a cloudless sunny day with an Aperture fstop of f/16 the ISO (film or sensor sensitivity to light) should match the value of the Shutter Speed.

Going back over that slowly may make more sense. If it’s a cloudless sunny day you can set your Aperture to fstop f/16 and with an ISO of X you would set the Shutter Speed at 1/X. If the ISO is 200 then the Shutter Speed should be 1/200. That is considered to be your Sunny 16 baseline. As conditions alter away from that baseline you can use the accompanying rules to estimate the number of stops (either Aperture fstops or Shutter Speed stops) to compensate.

Therefore, as the day becomes more cloudy the options are to either adjust that Aperture fstop value downward (to double the size of the hole in the lens) OR stop the Shutter Speed downward (to double the amount of light let through to the film or sensor). Using an ISO 200 example the adjusting Sunny Sixteen Rule baseline for Aperture OR Shutter Speed adjustments would become:

  • Snow/Sand: f/22 or 1/400
  • Sunny: f/16 with 1/200
  • Slightly Overcast: f/11 OR 1/125
  • Overcast: f/8 OR 1/60
  • Heavy Overcast: f/5.6 OR 1/30
  • Sunset: f/4 OR 1/15

To achieve a reasonable guess at any exposure the Sunny 16 Rule helps you to estimate the number of stops needing adjustment and use a combination of Aperture and Shutter Speed to achieve the correct exposure. The goal is to estimate the correct amount of light that needs to be exposed onto the film or sensor.

Sunny 16 Charts with a Constant Light

You are not locked into shooting f/16 on sunny days and you can start to make some compromises. For example, you may want to shoot in direct sunlight at f8. The important thing to grasp here is that given any ISO constant then a one-stop lower fstop with a one-stop faster shutter speed will give the same exposure. This is because the hole in the lens is doubled while the amount of time the shutter is open is halved (the same amount of light is exposed to the film or sensor).

It has been suggested that using ISO 200 with f8 at 1/800 could be the best compromise with nature photography.

ISO 100 Sunny f/16
1/50 1/100 1/200 1/400 1/800 1/1600
f/22 f/16 f/11 f/8 f/5.6 f/4
ISO 200 Sunny f/16
1/100 1/200 1/400 1/800 1/1600 1/3200
f/22 f/16 f/11 f/8 f/5.6 f/4
ISO 400 Sunny f/16
1/200 1/400 1/800 1/1600 1/3200 1/6400
f/22 f/16 f/11 f/8 f/5.6 f/4

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About the Author

Steven Clark Steven Clark - the stand up guy on this site

My name is Steven Clark (aka nortypig) and I live in Southern Tasmania. I have an MBA (Specialisation) and a Bachelor of Computing from the University of Tasmania. I'm a photographer making pictures with film. A web developer for money. A business consultant for fun. A journalist on paper. Dreams of owning the World. Idea champion. Paradox. Life partner to Megan.

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