Exposure compensation is a technique that many photographers have a hard time understand and master. But it doesn’t have to be that way. By understanding the basic principles behind exposure compensation and which scenes are likely to benefit from using it, you can use the right settings in your camera and get home with better-exposed shots. In this article, we explore what exposure compensation is and how it works.
What is Exposure?
In technical terms, exposure is defined as “the amount of light per unit area reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture, and scene luminance.” Photography is about light, and the exposure is the term that defines the right amount of light. There is correct exposure, and then there is underexposure and overexposure.
What is Exposure Compensation?
Exposure compensation, as it is called, is the manual change in exposure we make as an adjustment to the exposure recorded by camera meter. It is done in stops, with fractions of 1/3rd stops or even 1/4th stops possible in today’s camera. Exposure compensation is done to get the correct exposure when there is an underexposure or overexposure.
Underexposure and Overexposure – How the Camera Meter Works?
The camera meter is designed to meter light in a particular way. It essentially analyses the scene and expects everything to be at an average of 18% grays-tones.
However, if you shoot a white subject like a scene with a lot of snow in it, you will have exposure issues. The camera will underexpose the image as the camera meters or analyzes the scene and adjust the exposure settings (shutter speed, aperture, and ISO), to achieve a correctly exposed image with average tonal values of 18% gray.
In this case, with the snow, the scene in the frame isn’t an average of 18% gray, making the camera underexpose the image so the snow looks gray.
A black or dark subject will similarly be over-exposed to make the darker tones look gray. How do we break out of this cycle? We use exposure compensation. So if we know the subject is white and the camera meter will under-expose it, we can simply over-expose it by the degree we require, like +1 or +2 stops. The same is the case with a dark subject. If the scene is very dark, you can choose to underexpose the image with -1 or -2 stops to and get a better exposed image.
To beat the camera meter, we can meter a subject that appears somewhere in the middle of the exposure meter and is around mid-grays already. Here, it might actually be colored subject, but if its luminosity is around 50%, it will fall in this zone. We can do spot-metering to meter light from that part, and then shoot the subject at those settings. Or, as talked earlier, we can use exposure compensation to deal with the workings of the camera meter. It is also about the practice of the workings of meter and metering modes.
What is Correct Exposure?
Simply put, correct exposure is the one that makes us see the subject as it is in real life. So a white wall should appear white on the photo, and not dark or burnt out. Likewise, dark subjects should appear dark without looking washed out gray.
Ansel Adams talked about the Zone System of 11 different zones of exposure, 0 to X. He put the mid-tones in zone V, with zone 0 being absolute black with no details or texture and zone X being absolute white with no details or texture. The middle gray or zone V has clear north sky, dark skin, and average weathered wood, among other things for reference. Putting everything as per the correct exposure in their respective zones automatically turns the exposure right. However, the Zone System is complex to use, and haven’t found its way into neither the camera workings nor into the minds of most photographers.
Why Histogram Can Fail You!
Histograms are supposed to be a reliable tool for getting the correct exposure most of the time. However, histograms, like camera meter, are just a guide. They are not a sure-shot representation of your image. Sure they work fine on images that have an even balance between shadows, mid-tones, and highlights. However, there are high-key and low-key images, and there are images that don’t present a well-balanced histogram in its correct exposure.
For example, a high-key image will have the histogram almost towards the right (highlight) side while the low-key image will have it leaning towards the left. Like metering, there’s no right or wrong here. The most important feature of a histogram is that it allows you to see if there’s any white or black clipping (burning of highlights or darkening of shadows beyond recovery).
How Exposure Compensation works in Different Shooting Modes
Exposure Compensation works in different ways depending on the chosen shooting mode.
- For Manual Mode, exposure compensation is a guide. Since there are no automatic values, you can change the exposure via shutter speed, aperture, ISO, or their combination. The exposure meter here will show a marker in the zone the exposure is going without actually setting it to the middle of the meter, unlike in other shooting modes.
- For Aperture Priority Mode, the aperture is fixed. There are two scenarios that can work. In case the ISO is set to Auto the combination of shutter speed and ISO is used to change the exposure to fit the exposure compensation you set. In case ISO is fixed, only shutter speed is used to change the exposure.
- For Shutter Priority Mode, the shutter speed is fixed. Again, if the ISO is set to auto ISO, the exposure is set via changing the aperture and ISO. If ISO is fixed, only the aperture is changed.
- In both the above cases, if the aperture or shutter speed hits an edge of the value, then exposure compensation won’t be possible. If for example, you are using a 50mm f1.8 lens, with the aperture value of 1.8 in a shutter priority mode with ISO fixed. Now if you set an exposure compensation of +1, there’s no way the camera can do it. So it stays the same.
- For Program Auto Mode, most of the time the camera tends to change the shutter speed to get the same exposure, however, it might depend on camera and settings. In actuality, program auto mode gives you a set of settings. The dial, which changes aperture in aperture priority mode and shutter speed in shutter priority mode, changes the combination of settings in Program Auto Mode. So you need to check the correct set of exposure settings.
Exposure Compensation and Metering Modes
- There are three major metering modes in cameras, with some others being a byproduct of these. Each metering mode determines the scene we are shooting. For example, some scenes have a subject in the center, some scenes using negative space have a very small subject, while others have a complete scene of significance as far as exposure is concerned. The metering modes are:
- Spot Metering Mode: In this mode, the camera meters light only from a small portion of the image, usually the center 3.5%, though it may vary between 3-5%. Often, we meter from a small portion, say a human skin or a product, and expose the scene for that very subject. In this, we can directly use Zone System, which gives us an idea about the skin tones falling in a different zone. So if the skin tone comes in zone 7, we can expect the skin to be underexposed by 2 stops since the brighter skin will tend to move towards the darker one. We can then use +2 on exposure compensation and get the correct exposure. In theatre and performances, there’s usually a spotlight, and the rest is all dark. In such a case lies the practical usage of spot metering as apart from the subject, everything else is dark. Partial metering is present in some cameras, which meters about 8% of the sample instead of 3.5%.
- Evaluative or Matrix Metering: In this mode, the camera divides the scene into various modes. These scenes are individually assessed, and different factors are applied to get to the correct exposure. Factors such as the focus points, the highlights, darkness, distance, etc. are all taken into account. Nikon also compares the images to thousands of images in its database, and the way of calculating correct exposure varies from manufacturer to manufacturer, and sometimes even among different camera models from the same manufacturer.
In this form of metering, you need to assess the scene and then proceed. For example, in high-key photography, you will get a very darkened exposure if you go by the meter. You need to see the difference of exposure it is causing and then move accordingly. A high-key scene, natural or studio, may require you to use up to +2 exposure compensation settings.
- Center-Weighted Metering: In this mode, preference is given to the center of the frame while the outer portions are either feathered out in the exposure calculations or completely ignored. Unlike in evaluative metering, this doesn’t take into account the focus areas and merely focuses on the center of the image. Usually, the center 60% of the frame is given the most importance. It is an important metering mode that gives preference to center and hence is ideal for shooting portraits and wildlife.
In this form of metering, exposure compensation depends on the size of the scene and your priority. If the subject takes a large space, your exposure compensation settings will depend merely on the subject. If the subject takes less than 50% of the space, the surroundings will also have a slight impact on exposure. This metering is ideal for negating the backlight effect in shooting portraits. Hence, the camera will meter light only the subject and will ignore the backlight – which will thus be burned out.
Different Exposure Compensation Scenarios
Snowscapes and the 18% Grey Snow: Snowscapes, on any metering mode – unless you spot meter on some clouds or greens -will be giving you anything between an underexposure of 1.5 to 3. On an average, a 2 stop underexposure is common in snow. It’s, as described earlier, owing to the fact that as per camera meter, everything is 18% grey. So it turns white into grey. Without exposure compensation, we won’t be able to shoot the scene unless we keep working on it on manual mode with repeated attempts.
Nightscapes and the Brightening Noisy Red: Nightscapes are where we take pictures during the night, usually long exposures. These are on the opposite spectrum of snowscape. Metering brightens the scene by 2 to 4 stops making it appear like a false sunrise. The night pictures, however, require the night ambiance and the blanket of darkness. It makes the pictures contrasty and have us use the lights appropriately. Unless exposure compensation is used, it is very difficult to get the pictures right.
What Happens With Wrong Exposure and Why You Can’t Fix It In Post?
Wrong exposure, can break an otherwise good scene, completely. People often say that a wrong exposure can be fixed in post. Even in the digital age, though, it can’t be. If the exposure isn’t correct, other things also take a backseat. These are: white balance and sharpness. These are independent features on their own, but they get impacted by the correct exposure.
White balance is what makes the picture look like an original. Most of the modern-day cameras have excellent Auto White Balance. Even post-processing software allow us to fix White Balance, especially when shooting RAW. However, if the image is under-exposed or over-exposed, the color never comes out naturally. Even fixing it in post doesn’t do any justice to the natural color. White balance is essentially a way to correct all the colors in the images. When the product, portrait or a scene get light that is either more or less than the adequate, white balance goes off because the scene isn’t illuminated enough for it to determine the correct color balance. Even if you salvage exposure in post-processing, the dynamic range, which would have been highest on correct exposure, is lost. Hence, the get the accurate white balance and colors of the scene are almost impossible.
Sharpness of an image is also impacted by the exposure as well. Why? Because the sharp portions of the image not getting enough or too much light, thus impacting the camera’s ability to perceive the scene in its true sense. Dark white is gray, and gray has different properties than white. The sensor perceives it as completely different subject, and it becomes even more difficult in case it becomes underexposed or overexposed due to wrong exposure settings.
Get it Right in the Camera
Fixing exposure in post-processing is a common way of dealing with photographic exposure. While much of the parts can be fixed in post, it is never the same as getting it right in the camera. If you get the exposure right in the camera, you can take your images so much further with post-processing. It isn’t even about being a purist, it is simply about being ready to create the best image possible. For that to happen, we must understand exposure, metering, exposure compensation, and the zone system.