So, you've taken the time to learn how your camera works and finally feel comfortable giving manual mode a try, or at least more advanced modes like aperture priority or shutter priority mode.

The problem is, the photos you take when shooting in manual are all out of whack when it comes to exposure.

When you take photos in the daylight, your images are overexposed.

When it gets cloudy, your photos are underexposed.

And when it snows, you don't dare try shooting in manual mode.

Sound familiar?

If so, you're definitely not alone.

Many photographers - beginners, hobbyists, and enthusiasts alike - struggle to master shooting in varied lighting conditions, even after learning how to get out of fully automatic mode.

So what gives?

Really, all you need is a rule of thumb to help guide you in the decisions you make regarding your aperture, shutter speed, and ISO.

That rule of thumb is the Sunny 16 Rule.

The Sunny 16 Rule Defined

The Sunny 16 Rule states that on a sunny day, set your aperture to f/16, and then set the shutter speed and ISO values to the inverse of one another. So, if the ISO is set to 200, the shutter speed would be 1/200 seconds. If the ISO is set to 100, the shutter speed would be 1/100 seconds.

You get the point.

But why does it work?

Essentially, the Sunny 16 Rule works because it takes into account how aperture, shutter speed, and ISO work together to get a good exposure. That is, if you make a change in one of these settings, a change is required in another setting to maintain a good exposure.

That means that if the aperture is constant - in this case, f/16 - a change in ISO one way requires a change in the shutter speed the other way.

For example, if you increase the shutter speed from 1/200 seconds to 1/400 seconds, you reduce the duration of light that hits the camera's sensor by one-half. Without an adjustment to the ISO, the image would be too dark. That's why a corresponding move from ISO 200 to ISO 400 (which doubles the sensitivity of the sensor to light) helps you maintain a proper exposure.

This works for any of the exposure settings, too.

So, if you choose an ISO value of 200 and it remains constant, you have to adjust the aperture and shutter speed accordingly to maintain a well-exposed image. Check the chart below to see what I mean:

Note how in each scenario above that the ISO remains constant at ISO 200. Note as well that moving from f/16 to f/11 is +1 stop. That means you're doubling the amount of light entering the lens.

To prevent overexposure, you have to speed up the shutter speed to account for that extra light as a result of the larger aperture. That means that doubling the shutter speed from 1/200 seconds to 1/400 seconds is required.

That means that the exposure you got at f/16, ISO 200, and a shutter speed of 1/200 seconds will be the same as you get at f/11, ISO 200, and a shutter speed of 1/400 seconds.

Remembering this relationship - that a change in one of the three exposure factors requires an equal, opposite change in another, will help you make needed adjustments to account for all types of lighting conditions.

Other Applications of This Rule

There are several variations of the Sunny 16 Rule that help you identify the starting point for your exposure settings in a variety of lighting situations, as seen above. Let's explore each in more detail.

The Slightly Overcast f/11 Rule

When there's a few clouds in the sky, the amount of light available for your photos will be reduced. That necessitates using a slightly larger aperture than you would when it's sunny out, thus the movement from f/16 to f/11.

As we worked out in the previous section, using the same starting settings as the f/16 rule - an aperture of f/16, an ISO of 200, and a shutter speed of 1/200 seconds, we can determine what to do to keep a good exposure when a few clouds roll in:

Again, since f/11 represents +1 stop from f/16, you'll need to adjust another exposure setting by -1 to maintain exposure. That means changing the shutter speed from 1/200 seconds to 1/400 seconds.

When slightly overcast, start with the following settings:

• Aperture: f/11
• ISO: 200
• Shutter Speed: 1/400

The Overcast f/8 Rule

When even more clouds roll in, and more sunlight is blocked, you'll need to add +2 stops of exposure by moving from the sunny f/16 setting to f/8.

Again, because we've increased the amount of light entering the lens by two stops, we have to balance that out with -2 stops of shutter speed. That means changing the original sunny shutter speed from 1/200 seconds to 1/800 seconds.

When overcast, start with the following settings:

• Aperture: f/8
• ISO: 200
• Shutter Speed: 1/800

The Heavy Overcast f/5.6 Rule

On days when there just isn't much sun at all, you need to open the aperture even more, this time, from the sunny f/16 setting to f/5.6.

But since that move is adding +3 stops of exposure to the image, you have to compensate by dialing in -3 stops of shutter speed. In that case, you'd change from the sunny 1/200 second shutter speed to a new shutter speed of 1/1600 seconds.

When heavily overcast, start with the following settings:

• Aperture: f/5.6
• ISO: 200
• Shutter Speed: 1/1600

The Sunset f/4 Rule

When photographing sunsets, you need to open the aperture even more due to the fading light of the day. Change your original sunny f/16 setting to f/4, which is +4 stops. Compensate by changing your shutter speed by -4 stops to 1/3200 seconds. Doing so should result in an image that's just as well-exposed as if you used f/16, ISO 200, and a shutter speed of 1/200 seconds on a bright, sunny day.

When at sunset, use the following settings:

• Aperture: f/4
• ISO: 200
• Shutter Speed: 1/3200

Keep a Few Things in Mind

First and foremost, the Sunny 16 and its associated rules are just a starting point - they do not guarantee that the settings they recommend will get you a well-exposed photo each and every time.

What they will do, however, is get you started off on the right foot. With a few minor adjustments, you can more quickly and easily find the exposure settings that work for each unique lighting condition that you encounter.

Perhaps even more important is that the Sunny 16 and its associated rules account for incident light rather than reflected light.

The difference between the two is vital: incident light is a measure of the actual light of the scene, whereas reflected light (which your camera's meter measures) is the value of light that's being reflected.

This is important because if your subject is very bright, your meter might think the image needs to be darkened more than it should. Conversely, if the subject is dark, the meter might try to add too much exposure.

The Sunny 16 rule gets around this, though, meaning that you can often do a better job of measuring the light of a scene by using these rules than you can if you leave metering up to your camera.

Lastly, keep in mind that the Sunny 16 Rule works best for bright, even light. What's more, each of these rules is advantageous for scenes that are lit from the front or the side. That's because frontlighting and sidelighting can be tough on camera meters, so using these rules can get you closer to an ideal exposure.

Now it's time for you to give the Sunny 16 Rule a try! Before you do, if you need an in-depth overview of exposure, camera settings, and the Sunny 16 Rule, check out the video below by L. David Likes: