The Sunny 16 rule says that on a bright sunny day, an aperture of f/16 with a shutter speed close to 1 over your ISO gives a good exposure. It lets you set exposure by eye, which is handy with manual film cameras, a broken meter or a quick check on a digital body.
The Basic Rule
Set the aperture to f/16 and choose a shutter speed that matches the reciprocal of your ISO. At ISO 100 that means about 1/100 (most people use 1/125 or 1/100), and at ISO 200 about 1/200. Shadows should be clear and sharp edged for the rule to apply.
Adjusting for Other Light
When the sun is not at full strength, open the aperture by whole stops while keeping the shutter speed matched to ISO. These are general guidelines.
| Conditions | Shadows | Aperture |
|---|---|---|
| Bright sun | Sharp, dark | f/16 |
| Slight haze | Soft edges | f/11 |
| Light cloud | Faint | f/8 |
| Heavy cloud | Barely visible | f/5.6 |
| Open shade or dusk | None | f/4 |
How to Use It Step by Step
- Set your camera to manual mode.
- Choose your ISO, for example 100 or 200.
- Set the shutter speed to the closest value to 1 over ISO.
- Look at the shadows on the ground and choose the matching aperture from the table.
- Take a frame, and on a digital camera check the histogram and adjust.
If you want a different depth of field, trade settings in whole stops. Opening the aperture by two stops from f/16 to f/8 means shortening the shutter time by two stops too, for example from 1/125 to 1/500.
When It Is Most Useful
- Shooting film on a camera with no meter or a dead battery.
- Checking whether a light meter or auto mode is being fooled by a bright or dark scene.
- Working quickly outdoors when the light stays steady.
- Learning to read light, which makes you faster with any camera.
It works poorly indoors, in fast changing light, with backlit subjects, or on snow and sand, where you may need extra adjustment.
Practice Makes It Quick
Spend a week guessing the exposure before you look at your meter or screen. Walk outside, judge the sky and shadows, set the camera, and then check the result. After a few dozen tries you will begin to see the pattern at a glance, which saves time and builds a feel for light that carries over to every other camera you use.
FAQ
Does the rule work with digital cameras?
Yes. The light is the same, so it gives a useful first exposure. Use the histogram to fine tune.
What about the moon?
A similar idea called the Looney 11 rule uses f/11 for a full moon, with the shutter speed again matched to ISO. Treat it as a rough guide.
The Short Version
In bright sun, use f/16 and a shutter speed near 1 over ISO, then open the aperture as the light softens. It is a dependable fallback for film and a useful way to learn how light behaves.
