Exposure compensation is a function you can use to change the exposure set by the camera (camera-determined correct exposure) into something of your own preference. Here, we find out more about the function, and learn how to identify subjects that require positive or negative exposure compensation along the way. (Reported by: Tomoko Suzuki)

 

Exposure compensation is used to change the image brightness (“correct exposure") set by the camera

Points-to-note

- The exposure depends on the subject’s reflectivity.
- Use positive exposure compensation when the subject reflects light very well, and negative exposure compensation when it does not reflect light well.
 

Exposure compensation is a function that enables you to change the brightness from the camera-determined correct exposure. (For more about this, refer to Camera Basics #3: Exposure). To understand that better, let’s first look at how the camera measures exposure.

A camera has a built-in exposure meter that determines the “correct” exposure based on how much light the subject reflects (i.e., “subject reflectivity”). This process is called “metering”. There are several different ways this can be achieved, but the most commonly used metering mode is called “evaluative metering”. In this mode, the metering system breaks down the entire image area into a number of zones and measures the brightness in each zone to find an average. Evaluative metering is effective for finding the camera-determined correct exposure in most scenes.

However, the camera-determined correct exposure does not always result in the optimum brightness for the scene. If a subject is black (or close to black) in colour, most cameras will tend to over-expose, resulting in a very bright image. Conversely, if the subject is white (or close to white) in colour, most cameras will under-expose, resulting in a dark image. This is because white has high reflectivity (reflects a lot of light), whereas black has low reflectivity (reflects little light).

This is where you can use exposure compensation to manually adjust the brightness to something more ideal. Normally, exposure compensation is set to the “0” position, but you can adjust that with the exposure compesnation dial or button. We usually compensate towards the “+” range for subjects with high reflectivity, and towards the “-“ range for subjects with low reflectivity. Having said so, there is no right or wrong where it comes to exposure compensation, so you can also use it to tweak image brightness to suit your creative intent or preference.

 

Scenes that require exposure compensation

Positive (+) exposure compensation
Subjects shot in backlight, highly reflective subjects (white or close to white in colour) and bright scenes will result in photos that look darker than how the scene really appears to the naked eye. In such cases, use positive exposure compensation.

 

Negative (-) exposure compensation
Subjects with poor reflectivity (black or close to black in colour) and dark scenes will result in photos that look brighter than how the scene really appears to the naked eye. This could cause colour detail to be blown out, especially when you are capturing scenes with dim surroundings, such as sunsets. Using negative exposure compensation will help you to restore the colour.

 

Exposure is usually stated in terms of EV units
The exposure compensation range differs between cameras, but usually ranges between EV-5.0 to EV+5.0. Setting exposure compensation by 1 EV in the positive direction (EV+1.0) increases the brightness to twice the original amount, while setting it by 1 EV in the negative direction (EV-1.0) results in a brightness that is half the original amount. 1 EV is equivalent to 1 f-stop.

 

 

Concept 1: “+” for whites, “-” for blacks

White or whitish subjects such as pale sandy beaches or snowy scenes have high reflectivity, which means that they will appear dark if you shoot in an auto-exposure mode. For such subjects, apply positive (+) exposure compensation. If the white areas cover a huge portion of the image area, you will probably have to set an extreme positive exposure compensation value.

Left: EOS 5D Mark III/ EF50mm f/1.4 USM/FL: 50mm/ Aperture-priority AE (f/1.4, 1/200 sec, EV±0)/ ISO 100/ WB: Manual
Right: EOS 5D Mark III/ EF50mm f/1.4 USM/ FL: 50mm/ Aperture-priority AE (f/1.4, 1/100 sec, EV+1.0)/ ISO 100/ WB: Manual

On the other hand, subjects that are black or close to black in colour, such as nightscapes with many shadow areas, tend to be captured as images that look brighter and lighter than the actual scene as seen with the naked eye. If you want the scene to look more solemn, apply just enough negative (-) exposure compensation so that the brightest part of the image looks just a little bit darker. Negative exposure compensation also works well for making colours look more intense—try it out the next time you take a picture of sunset.

 

Left: EOS M/ EF-M22mm f/2 STM/ FL: 22mm (35mm equivalent)/ Aperture-priority AE (f/2, 1/50sec, EV±0)/ ISO 100/ WB: Daylight
Right: EOS M/ EF-M22mm f/2 STM/ FL: 22mm (35mm equivalent)/ Aperture-priority AE (f/2, 1/100 sec, EV-1.0)/ ISO 100/ WB: Daylight

 

 

Concept 2: Auto Exposure Bracketing

For scenes where it is hard to determine the exposure, use the Auto Exposure Bracketing (AEB) function. It allows you to automatically take 3 (or more) shots of the same scene, each at a different exposure. The size of the difference in exposure between each shot depends on the camera, but you could take shots that vary as slightly as 1/3 of an f-stop from each other. When you are done shooting, you can choose the shot that has your ideal exposure.

This setting allows you to take 3 shots at intervals of EV±0.5 from each other.

 

Exposure compensation: EV+1.0
EOS 5D Mark III/ EF70-200mm f/4L IS USM/ FL: 200mm/ Program AE (f/8, 1/320 sec, EV+1.0)/ ISO 400/ WB: Daylight

 

Exposure compensation: EV±0
EOS 5D Mark III/ EF70-200mm f/4L IS USM/ FL: 200mm/ Program AE (f/8, 1/640 sec, EV±0)/ ISO 400/ WB: Daylight

 

Exposure compensation: EV-1.0
EOS 5D Mark III/ EF70-200mm f/4L IS USM/ FL: 200mm/ Program AE (f/8, 1/1250 sec, EV-1.0)/ ISO 400/ WB: Daylight
I shot a backlit scene using AEB at intervals of EV±1.0. The optimum exposure for this shot is EV+1.0. Setting the AEB intervals to 1/3 or 1/2 stops allowed me to capture shots that had slighter differences in exposure, and choose the most appropriate one afterwards.

 

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