Measuring and setting the correct exposure

Submitted by WhiteWall Team

Correct exposure metering

Photography is "painting with light". Above all, you need to correctly assess and measure the light in order to capture the perfect image. Once you have mastered the basic camera techniques of the exposure triangle (aperture, shutter speed, ISO), focus and depth of field as well as white balance, there is another decisive value that you can influence: the exposure metering of your camera. We will show you what is important here.

In order to expose your images correctly, you need to capture the surroundings and the available light in your shots. This process primarily takes place in the camera and fundamentally influences every image. Of course, the aperture, exposure time and ISO are the most significant factors in the creation of a shot. But just as the white balance plays its part, the exposure metering also has a direct influence on the result of your shot.

Exposure metering in the camera

From the early days of photography to the present day (for example with analog cameras without an integrated light meter), special hand-held light meters are used to determine the correct exposure. On the one hand, these measure the incident light on the object. This way, the photographer knows which settings to make on the camera. The great advantage of such a procedure is that the actual incident light is measured and not its reflection.

However, most photographers today no longer have a classic light meter in their pocket. Nowadays, you can rely on the powerful light sensor in your digital camera to take all-round successful photos.

The basic values of your camera

When measuring exposure, every camera always assumes a subject that reflects 18 percent of the brightness. This is the 18 percent that the gray card also provides for the white balance, which is often used in studio photography.

Based on this value, the camera then calculates in the exposure modes how long the shutter needs to be open, for example. So bear in mind that a completely white sheet of paper is 18 percent gray according to the measurement and a black background should be exposed long enough for it to take on this shade of gray. To avoid this dilemma in the program modes, there is the manual mode "M", in which you make the settings by hand. In addition, modern digital SLR and system cameras often have their own processor to determine the exposure in order to ensure the highest possible accuracy.

The set metering

Every time you press the shutter release button of your camera halfway, the autofocus focuses on its metering point and the exposure metering runs in the background. You can read the result - in the manual mode of your camera - on the small scale at the bottom of the screen or in the viewfinder. This scale, which goes from "-3" in thirds to "0" to "+3", shows you whether you are currently overexposing, underexposing or whether the exposure is suitable for your subject. Depending on the result, you can move the arrow to zero by changing the aperture, the exposure time or the ISO value and take an optimally exposed picture. Tip: You can also deliberately underexpose or overexpose your subject in the automatic or semi-automatic mode of your camera in order to influence the result of your shot according to your wishes.

Whether zero delivers the result you want naturally depends on your artistic goal. Do you want to create a high-key or low-key image, capture a hard contrast or deliberately underexpose in order to have more information on the data set in post-processing? Then you need to incorporate these thoughts into your metering and, if necessary, intervene if the camera's automatic system has other plans.

Functional methods of light metering

The light sensor measures the incident light that hits the camera's sensor. The variable settings are made on the basis of this measurement. This is not a fixed procedure, but a metering method previously set in the menu. In general, all cameras have the same repertoire of measurement methods. We present them to you.

1. spot metering for sports, action and portraits

With spot metering, only a small part of the entire metering field is taken into account by the exposure sensor. The practical thing about this is that this is usually the same point that is selected with the focus point during autofocus. This means that the area that is focused is often identical to the spot that is also scanned for light metering. Depending on the sensor size, the spot corresponds to around five percent of the area.

The preferred application for spot metering is in those situations in which the autofocus is also limited to one point. These are usually challenging subject situations. For example, if you want to capture fast movements, such as a bird in flight or a sports car at full speed. Spot metering concentrates on the subject and ignores the rest of the surroundings. This also makes it interesting for portrait photography, where the focus is on the eyes.

2. center-weighted metering for portraits and animal photography

With center-weighted metering, the focus of the exposure metering is in the center of the image and tapers off more and more towards the edges. It takes up around 60 to 80 percent of the image area. The advantage of this metering method is that a larger area of the subject is included in the metering.

Some cameras have the option of adjusting the size of the off-center area or the strength of the weighting. The disadvantage is already in the name: The metering focuses on the center. As soon as the rule of thirds is used or the subject is not in the center, the exposure metering can be off, as it uses a non-image-relevant part more strongly to determine the exposure.

This method is particularly suitable for portraits. Although the focus is on the eyes, the metering takes the whole face into account. The advantages of this metering also come into play when taking pictures of animals.

3. multi-segment metering as a universal talent

Multi-segment metering combines the best of both worlds and is therefore an almost perfect tool for numerous images. Multi-segment or matrix metering is therefore rightly preset on most cameras. With this method, the image is divided into various small areas and the light sensor measures and analyzes these individually. The focal length and object distance are taken into account and even typical situations or scenes are recognized. In contrast to center-weighted metering, the set focus point plays an active role here and its position is included in the calculation.

This metering is usually the ideal choice for landscape photography. This is because the detailed scanning allows distance, colors and different brightnesses to be detected and an optimal exposure to be determined.

As this metering method often works together with other intelligent systems in your camera, there are further advantages. For example, if the face or eye detection of the autofocus system is activated, both the face and the immediate surroundings are correctly exposed.

4. integral metering

This method of light metering is slowly disappearing and is very often replaced by the versatile multi-segment metering (see above). Nevertheless, integral metering is still very popular in older digital cameras. To calculate the appropriate exposure, the entire image area is scanned equally - without weighting, as is often the case with multi-segment metering. As a result, integral metering determines an average value that is then applied to the entire image.

This metering technique is particularly suitable for balanced environments without particularly bright or dark areas. It shows its strengths in landscape photography with monotonous surroundings or large buildings, such as churches, with uniform illumination. In general, however, modern exposure algorithms are superior to integral metering.

5. selective metering

Similar to integral metering, selective metering is rarely found in new camera models - if at all. It takes between ten and 15 percent of the image area into account for its calculation. Compared to spot metering, this method therefore takes a larger area into account.

Selective metering is therefore the first choice when slightly more than spot metering but considerably less than center-weighted metering is required. It can be used, for example, to capture artistic still lifes with strong contrast.

Clever helpers in the camera

The histogram

The best tool in your camera for checking the exposure is the histogram. This is a great help when it comes to reliably recognizing overexposure and underexposure. In landscape, travel and architectural photography in particular, the histogram is a real must-have. Because in these photo genres, it is crucial to display the entire subject with fine detail and sufficient contrast.

The histogram analyzes the black and white version of your image in 255 levels. The darkest areas are on the far left, the lightest on the far right. The more areas are assigned to a tone value, the higher the bar rises in the graph. It is therefore a purely quantitative and not a qualitative representation of your subject.

One glance is enough to recognize the illumination. If the tonal values accumulate in the middle and run out towards both edges, the subject is evenly exposed. If the deflections are stronger on one side, the image tends to be overexposed (right) or underexposed (left). Tip: If you take photos in RAW format, you can often compensate for underexposure in post-processing, as the format records a sufficient amount of data and this can be restored. This is not the case with overexposure, which usually cannot be corrected afterwards. It is therefore better to underexpose than overexpose!

Exposure compensation

Exposure or EV compensation can be found on most camera models as a wheel or by the symbol (diagonally divided square, black half with white plus, white half with black minus) as a button.

If the value on the scale is changed, all camera settings, i.e. the set aperture, exposure time and ISO, remain unchanged. The selected white balance and exposure metering are also at the previously selected level. However, you "override" the exposure metering of your camera and influence the result according to your wishes.

The entire image is then displayed either brighter or darker. As soon as the setting is made in one direction, the arrow in the exposure display scale moves to the left (darker) or right (brighter).

Ideally, the setting is always set to zero and is only used if the other values cannot be influenced - for example, for a long exposure or an aperture setting that you absolutely want to retain.

Important: Remember that the use of graduated or neutral density filters (ND filters) also affects the exposure metering. Your exposure display will change after attaching a filter, particularly due to any reflections on water that may have stopped.

Conclusion

Manual or automatic exposure metering is essential for every shot. This is because it has a significant influence on the final result. Modern digital cameras generally have an integrated light meter and in some cases their own processor for determining the correct exposure. Traditional manual light meters are almost only used in analog photography if the camera in question does not have a built-in light meter.

In combination with modern algorithms, the results of modern exposure metering systems are very reliable and versatile. This means that you can take the perfect picture of practically any subject situation. On the other hand, the manual mode of your camera also allows you to set your exposure settings completely independently using aperture, shutter speed and ISO. Depending on the aim and desire of your creative idea. Try it out and experiment with the different exposure modes offered by your camera.