Going Manual: Learning Exposure Basics

Written by: Jeff

Exposure is probably the most dreaded subject in photography. We know a lot of photographers who have been shooting for years but still rely on their camera’s metering system to dictate a scene’s exposure. Cameras are getting more and more advanced which is why it works, but it will not work all the time. This is why even the most advanced DSLRs still have exposure compensation features.

With a few simple guidelines, you can start shooting in full manual and stop relying on your camera to meter for you. The most important rule I learned when I first started shooting in manual mode was the Sunny f/16 rule. However, we first have to start with what we mean by exposure.

At its most basic level, exposure is how much light you allow to reach your sensor. The amount of light is the result of the interaction of three factors: ISO, aperture opening and shutter speed.

ISO

ISO (International Standards Organization) also known as ASA (American Standards Association) is the rating scale used to determine how sensitive a film is in recording light. The same scale is used when referring to the sensitivity of a digital camera’s sensor. Depending on your camera, you can change your ISO setting between 50, 100, 200, 400, 800, 1600, 3200 and 6400. You can see that each number is double the preceding number and each step also represents a doubling of the film or sensor’s sensitivity to light.

A lower ISO number means that the film or sensor is less sensitive to light. This is the reason why most people bump up their ISO setting when shooting in low light since they need less time to expose for a shot. The problem is that your camera’s sensor loses its ability to record detail the higher the ISO is. This means that your photos will be less sharp and have more noise which is never a good thing.

APERTURE

Aperture refers to the opening inside the lens where light passes through. The size of the opening is measured in f-stops expressed as f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f22 and f/32. Starting from f/1 each step in the series represents a halving of the amount of light reaching the camera’s sensor or what is called a full stop. Most DSLRs now give you the ability to select ½ or 1/3 stops so you might see more aperture values than those listed above but for the purpose of this article we will only focus on full stops.

SHUTTER SPEED

Shutter speeds represent how long the camera’s sensor is exposed to light and is measured in seconds. Shutter speeds run from 30, 15, 8, 4, 2, 1, 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. Again, each number is double than the preceding value and also represents double the amount of light reaching the sensor.

Here are some rules of thumb regarding shutter speed. To take sharp photos, your shutter speed must be equal to or more than the reciprocal of your focal length for non moving subjects. So if you’re shooting at 50mm, your shutter speed must be at least 1/60. To freeze movement in your photos, you must be shooting at least at 1/500.

THE SUNNY F/16 RULE

The Sunny f/16 rule is a method developed to correctly expose a photo without using a light meter. It states that in a clear sunny day, you can set your aperture to f/16 and your shutter speed as the reciprocal of your ISO.

Let’s say you’re in a park in a clear day and you want to take a photo using this rule. The first thing you have to do is to set your aperture to f/16. You then need to check your ISO setting. If you are on ISO 100 then your shutter speed should be set to 1/125. If you’re at ISO 200 then your shutter speed should be at 1/250. Note that not all ISO settings will correspond to an exact reciprocal when selecting your shutter speed so just select the nearest one.

If the scene is slightly overcast then open up your aperture one stop to f/11. If it’s overcast, open up two stops to f/8. If it’s deeply overcast, open up three stops to f/5.6. I know that the terms sunny and overcast are very relative so how do you know what aperture setting to use? The first thing you should check is the shadow detail in the scene. If the shadows are very distinct then it’s considered sunny. If the edges of the shadows are soft then it’s slightly overcast. If the shadows are barely visible then it’s overcast. If there are no shadows then it’s deeply overcast. You can also refer to the chart below.

USING THE SUNNY F/16 RULE CREATIVELY

Now that you’re familiar with the basics of the rule you can start getting creative with it. Let’s say you want to take a photo of a bee in a slightly overcast setting using ISO 100 but you want to use an aperture setting of f/4.5 to eliminate the messy background. Using the basic rule, you start at f/11 with a shutter speed of 1/100. Since f/4.5 is approximately three stops lower than f/11, you have to compensate for the increase of light reaching your sensor using your shutter speed or you will get an over exposed shot.

Opening the aperture by three stops is equal to increasing the shutter speed by three stops since going from one level to the next in the aperture and shutter speed scales correspond to the same amount of light being lost or gained. On a slightly overcast day using f/4.5 you can set your shutter speed to 1/800 at ISO 100 to get a properly exposed shot.

CC Photo by Beyond Megapixels 105mm at ISO 100, f/4.5, 1/800
You can also start your computations with the shutter speed. Let’s say you want to take a photo of a dog on the beach and you want to freeze all movement in the scene. You check the light conditions and decide that it’s sunny and you are at ISO 80. Again, starting with the basic rule, you set your aperture to f/16 with a shutter speed of 1/60. Since you want to eliminate any motion blur you decide to use a shutter speed of 1/1250. Since 1/1250 is about four stops higher than 1/60, you need to compensate for the loss of light by setting your aperture to f/4.5.

CC Photo by Gungnir 76mm at ISO 80, f/4.5, 1/1250
There is an ongoing debate today on how use the Sunny f/16 rule. Some say that the subject must be facing the light for it to work. Some say that you can still get a properly exposed shot even if the subject is lit from the side. What I think is that like all the rules in photography, the Sunny f/16 is just a starting point to studying light and how to properly judge the exposure of a scene without being dependent on your camera. With enough practice, you’ll be able to judge a scene’s proper exposure before you even raise the camera to your eye.

Related Posts:
Starlight Effect: Creative Use of Aperture
When to Use Exposure Compensation

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© 2007-2008 Beyond Megapixels

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