- Exposure Automation is Amazingly Accurate
- 18 Percent Gray
- Exposure Compensation Examples
- How to Use Exposure Compensation
- Increase or Decrease Exposure Compensation?
- What Does Exposure Compensation Do?
- Creative Control and Inaccurate Meter Readings
- National Geographic Photo Basics: The Ultimate Beginner's Guide to Great Photography
- Photography: The Definitive Visual History
- Read This if You Want to Take Great Photographs
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- How to Get a Well-Exposed Image
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What is exposure compensation and why should we use it? Exposure compensation is a camera tool that allows a photographer to control the exposure either for correction or for creative reasons.
In order to have exposure compensation explained properly, we need to have an explanation of when and why an exposure meter might be wrong.
Table of Contents
Exposure Automation Is Amazingly Accurate
Most modern cameras have a metering system that is so smart and versatile that we could trust it in all but the most challenging lighting and exposure situations. Evaluative metering is the norm for automatic modes.
With automatic exposure, a photographer can concentrate on other aspects of the photographic process, such as focus, composition, perspective, or posing a subject.
As a photographer, though, we tend to be concerned about light and exposure. For good reason, the heart of the photographic process is light and controlling that light somehow. One of the first things beginner photographers should learn is the Exposure Triangle.
The Exposure Triangle tells us that there are three variables we can control, or let the camera control, in order to adjust exposure. All three are intertwined. If you change one, the other two are affected.
The three variables are shutter speed, or how long long we allow light into the camera, the lens aperture or f-stop, which controls how much light the lens lets in, and finally ISO, or the sensitivity to light of our recording medium, whether film or a digital sensor.
What exposure compensation allows a photographer to do is to leave the camera in an automatic exposure mode, and yet have input into how the meter adjusts the camera exposure settings and controls.
An important part of understanding exposure compensation is to know exactly what our camera exposure meter is actually doing.
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18 Percent Gray
The world is not all one color or one exposure value. A basic value for exposure metering is that the middle gray value of 18 percent gray is representative of average scenes in terms of exposure value.
This standard value is based on logarithmic math. In order to use meters and all the exposure calculations involved, we really aren’t required to remember complicated mathematical formulas. It is enough to understand that exposure meters are designed to see the world as 18 percent gray, with that number being the middle of the range on a logarithmic scale.
For an excellent and short YouTube video explanation of 18% gray, check out the video above by Filmmaker IQ.
For every scene in front of your camera, the meter is going to treat it as though the light values average out to middle gray. It’s when the scene doesn’t actually fit that average that incorrect exposure can occur. This is why many professional photographers use an 18 percent gray card to get a correct exposure.
Exposure Compensation Examples
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The two common examples of exposure compensation are scenes or subjects that are either dominated by very dark or very light areas. The camera meter will attempt to fit them into its middle gray expectation. A darker value will be overexposed, a lighter value will be underexposed.
As real life examples, let’s look at a couple of likely situations where you would want to make use of exposure compensation.
In one situation, we’re at a scene that has large areas of bright white snow, bright white sand, or highly reflective water. This could be on vacation at a ski resort, a tropical beach, or on the water, either at sea or on a lake.
Our eyes see the brightness and our brain interprets it accurately. Not the exposure meter, however. Even with very well designed evaluative metering, the camera will attempt to render the brightness, reflectivity, or whiteness into the 18 percent gray it expects. It will underexpose.
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Another situation is usually handled pretty well with modern camera automation is a subject with a strong light source behind it. Even though the evaluative metering probably has a solution already programmed for this situation, it still tends to underexpose for the actual subject.
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At the opposite end of the possible situations is a scene dominated by dark values. A hyperbolic situation often cited is a black bear in a dark forest. A portrait subject in dark clothing against a dark background is another example. The subject is full of dark tones, but the meter will want it all to be closer to middle gray. So it will overexpose.
How To Use Exposure Compensation
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You could take your camera out of automatic modes and use fully manual settings for shutter speed and aperture. Still, many of us would probably use an exposure meter, maybe a handheld one, to get us into the right ballpark.
As an alternative to full manual exposure settings is the exposure compensation control on our camera. The exposure compensation control is usually pretty easy to find on our camera. Look for a button or menu option that has “-+”, “+-”, or “ExpComp” on it, like so:
Exposure compensation button on a Canon EOS Rebel T7i.
Exposure compensation button on a Nikon Z6.
This control is quite variable. A large number of cameras have exposure compensation capability of plus or minus at least two stops. Some have 3 or more stops available. The exposure compensation can usually be adjusted in fractions of a full stop, either ½ or ⅓ stops.
A stop of exposure is a concept we should already know if we have learned the Exposure Triangle. Each full stop of exposure change either halves or doubles the actual exposure value, since it is calculated on a logarithmic scale with a base of 2. This is discussed in the video above by Photo Genius.
A change of shutter speed from 1/125th to 1/60th allows twice as much light. A change from an aperture of f/2.8 to f/4.0 lets in half the light. A change of ISO from 200 to 400 doubles the light sensitivity of the sensor.
Likewise with exposure compensation controls. Setting +1 stop will double the exposure, -1 will halve it. So that’s a basic answer for the question of what does exposure compensation do? Now, back to those examples.
Increase Or Decrease Exposure Compensation?
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The scenes of the beach full of bright sand, snow covered ground, or a super reflective expanse of water will all be underexposed by the camera meter. The exposure compensation needs to be on the plus side, adding exposure. In many instances, a value of plus two (+2) is a good choice.
Likewise with the subject having a very strong light source behind them. Adding 1 or 2 stops of exposure compensation will probably work. That's +1 or +2 on the exposure compensation dial.
Now to the black bear in a dark forest. Or it could be your black kitty on your dark leather couch. A twilight or Blue Hour cityscape is another similar exposure situation. The camera wants to overexpose it to get back the middle gray it expects.
Therefore, you will want to override control of the automation by dialing in a minus or negative value: -1 or -1 ⅓ is a good starting point.
What Does Exposure Compensation Do?
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In other words, what exactly happens when you add or subtract value in exposure compensation? Well, that depends on what automatic you are using.
As a word of caution, if you are in your camera’s Full Auto mode, sometimes I call this the Green Dot mode, you can’t set any exposure compensation. The camera has complete control over the entire Exposure Triangle. It may even adjust ISO for you, a setting that we usually carefully choose ahead of time or at the beginning of a photoshoot.
The Green Dot auto mode will choose every camera setting for you: Focus mode and focus points, pop up flash, and all exposure settings. This is great for quick grab shots, but with no photographer input other than zoom and where to point the lens.
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In aperture priority mode, where you choose the f-stop and the meter sets the shutter speed, exposure compensation will only change the shutter speed. So, you will need to watch out for speeds that are too slow to comfortably hand hold.
For shutter priority mode, you are choosing shutter speeds and camera meter adjusts f-stops, the exposure compensation will change the aperture. If you have selective focus or deep depth of field concerns, pay attention to how that is affected by aperture changes.
Programmed auto mode, the P that isn’t the Green Dot setting, both shutter speed and aperture will change, usually equally, with exposure compensation.
Can you use exposure compensation in manual mode? Yes, but why bother? You’re already fully overriding the camera controls. Attempting to use exposure compensation in manual mode will just confuse the issue.
Creative Control and Correcting Inaccurate Meter Readings
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The two reasons for using exposure compensation in any of your camera’s automatic modes are for the exposure corrections already mentioned, plus others similar to those, and for doing what photographers love to do, be creative.
A creative approach to photography often demands that we take control of the camera settings. With exposure compensation, we can gain control even while still using the amazing exposure automation of our modern DSLR or mirrorless camera.