The Nikon D850’s matrix metering, combined with the RAW format, preserved details in both the highlights and shadows without the need for any exposure compensation. 1/60 s at f/8, ISO 100, Nikon AF-S 50 mm f/1.4.
Light metering is essential for the camera to capture the desired image. Whether you use automatic or manual mode, the camera’s built-in light meter or a separate light meter, here are the keys to proper exposure.
Digital cameras measure light with a high degree of sophistication to handle all lighting conditions, whether natural or artificial. At the heart of this measurement is the light meter. It generally operates in four modes: evaluative (also called matrix or multizone, depending on the brand), center-weighted, spot, and full-frame.
Intelligent Metering
Evaluative metering compares the luminance levels of the scene to those of a series of reference images stored in the camera’s software. It can even take faces into account. The aperture-shutter speed setting is determined based on the ISO sensitivity, in order to preserve detail in both highlights and shadows.
This mode delivers good results for everyday shooting, especially since exposure errors can often be corrected in post-production with RAW files. It’s worth noting that the sensors are more tolerant of severe underexposure than of excessive overexposure.
Like Sony, the measurement modes are indicated by several icons.
- Multi: Optimal exposure is calculated based on the luminance of multiple areas of the image.
- Center: Measures the average brightness of the entire image, with an emphasis on the central area of the screen.
- Spot: Measures a specific part of the image. The size of the metering circle is adjustable.
- Entire Screen: Measures the average brightness of the entire image.
- Highlights: The metering takes into account the brightness of the highlights to prevent overexposure.
18% Gray, Standard Metering Mode
The other metering modes—center-weighted, spot, and entire screen—are based on the principle that most common scenes reflect, on average, 18% of the light they receive. This is the standard principle used by light meters. The aperture-shutter speed setting is calculated based on this criterion.
Interpretation of the measurement is often necessary, as it reduces everything to an average gray level of 18%, which is suitable for neither very bright nor very dark subjects. Center-weighted metering focuses on the center of the image, spot metering on a central circle corresponding to 5% of the image, and entire screen on the entire frame.
Some cameras offer more sophisticated modes: spot metering for highlights and shadows, matrix metering with specific consideration for highlights, etc.
Exposure meters—whether built into cameras or standalone—are calibrated based on the principle that the most common scenes reflect, on average, 18% of the light they receive. Gossen document.
Spot Metering
Spot metering is very useful. It calculates exposure based on a specific area and helps you assess which part of the image is at risk of irreparable overexposure. Depending on the sensor, a deviation of +2.5 to 3.5 EV from the spot metering reading is tolerable in RAW files, with highlights that can be recovered in post-production.
For example, for an area metered at 1/1000 s at f/8, if the actual exposure of the shot is 1/125 s at f/8, there is a +3 EV difference compared to the metering reading.
It was popularized by Ansel Adams and his Zone System technique following the release of the first spot meters (the SEI Photometer, in 1948). Today, the only model on the market is the Sekonic L-858D, which combines both incident light metering and spot metering. Spot metering is performed over a 1° angle. Spot metering with a 35mm camera or full frame camera) equipped with a 50 mm lens corresponds to approximately 5° (shown in red on the building). The spot meter is therefore more accurate for measuring small areas. This is useful for determining the difference between the aperture-shutter speed settings for a shot and the brightest areas in high-contrast scenes. If this difference exceeds 3 EV, there is a risk of complete loss of detail, even with the ability to recover highlights in RAW format.
Checking the Exposure
With an SLR camera, you can check the shot after taking it. The rear screen can display clipped areas and the image’s histogram. If the exposure isn’t right, you can remake the photo. This approach works with a static subject, when the lighting doesn’t change, whether outdoors or in a studio.
When conditions are changing, anticipating the situation is essential to avoid excessive overexposure or underexposure. With a mirrorless camera, you can check the exposure instantly, since the histogram and highlight clipping can be displayed in the viewfinder at the moment the shot is taken.
In Live View mode, highlight clipping warnings (shown here in red) can be enabled. In the viewfinder, the histogram display—which is maxed out on the right and shows a vertical red line—indicates highlight clipping. Here, a -1 EV compensation is selected. Olympus OM-D EM1 MkII in Aperture Priority (A) mode.
Anticipating the Exposure
It’s very tempting to let the camera decide for you with an automatic exposure mode (aperture priority, shutter priority, or program mode) and adjust the image in post-production. This approach often works. But it can sometimes be problematic with subjects that have a wide dynamic range—such as high-contrast scenes and backlit subjects—when you want to preserve detail in the highlights.
On a mirrorless camera, the histogram can be displayed in the viewfinder: simply set the camera to matrix metering and avoid letting the histogram hit the right edge. In manual mode, you adjust the shutter speed or aperture. With the automatic modes P, S, or A, you adjust the exposure compensation.
With an SLR, if you need to work quickly, point the camera at the highlights, lock in the exposure settings, frame, and shoot. Just as a musician practices their scales, you regularly practice by shooting under a wide variety of lighting conditions to master the necessary adjustments based on your light meter’s readings. That’s what it takes to be a pro.
It’s by practicing with subjects in extreme lighting conditions that you master the art of exposure. Nikon D850, 17–35 mm lens, 1/25 s at f/11, ISO 100.
The Smartphone as a Light Meter
Every profession has its tools. The standalone light meter is part of a photographer’s traditional arsenal, especially in film photography. But with today’s digital cameras, is it still useful? Smartphone light meter apps, such as myLightMeter or LightMe, make up for the lack of a light meter in older film cameras. But they aren’t always reliable. Another limitation is that they are limited to measuring reflected light.
When the subject reflects light at levels below or above 18%, incident light metering is more effective: there’s no need to compensate for the exposure readings from reflected light metering. But this method has a constraint: the measurement must be taken close to the subject, with the light meter pointed toward the camera. Incident light requires an integrating dome, such as the one on the Datacolor LightColor Meter, connected to a smartphone via a dedicated app.
An app like myLightMeter turns a smartphone into a reflected-light meter. The more sophisticated Datacolor LightColor Meter app and its sensor provide highly accurate incident-light measurements. Datacolor document.
The Standalone Light Meter
Standalone light meters have the advantage of combining, in a single device, the software function (i.e., exposure calculation) and the measurement tool for both reflected and incident light. New models from Gossen, Kenko, or Sekonic are a guarantee of reliability. The most sophisticated model is the Sekonic L-858D, which is compatible with high-speed flash synchronization and capable of measuring flash duration.
The standalone light meter offers both reflected and incident measurement modes. On the Gossen Sixtomat Digital light meter, the incident measurement dome slides to the side to make room for reflected measurement (the lens is visible in the center). On the Sekonic light meter, reflected measurement is performed in spot mode.
Portrait Photography Using Incident Light
In the studio, back when film photography was the norm, flash and continuous light were adjusted using incident light. In digital photography, this type of measurement remains relevant, if only to control the intensity of the lighting and the ratio between highlights and shadows. It’s also a way to learn how to take control of the light.
The light meter is placed near the subject to measure the light falling on it. The white dome is pointed toward the camera.
Artwork Reproduction
Precise light distribution is essential for artwork reproductions (here, a work by Simone Francq). Most standalone light meters display readings in 1/10-stop increments—a level of precision that no camera can match. Incident light remains the gold standard.
The light meter measures the light at the four corners of the subject being photographed to ensure that the lighting is evenly distributed.
Fast as a Flash
It’s impossible to gauge the intensity of a flash with the naked eye. Most light meters compatible with flash lighting take readings for sync speeds up to 1/500 s or 1/1000 s. The Sekonic L-858D can go up to 1/16000 s. To freeze fast-moving action with a flash, knowing its duration is essential. The Sekonic L-858D offers flash measurement from 1/40 s to 1/55,500 s. At 1/8,000 s or faster, you can be sure to freeze even the fastest movements.
Flash metering indicates the aperture setting based on the shutter speed and ISO sensitivity. Here, we have F/5.62 at 1/8000 s and ISO 400. The flash duration, here 1/28,100 s, is generally given as “t0.5,” which is the effective duration of the flash. “t0.1” is the total duration of the flash. After the flash fires, the point at which the maximum intensity has decreased by half is called “t0.5.” The point at which the intensity is equal to 1/10 of the maximum intensity is called “t0.1.” 38.3 us corresponds to 38.3 microseconds, or 1/28,100 s.
Discover the professional photography courses at Spéos
Spéos photography school offers professional photography programs in 1 year, in 2 years, short photography programs (in 2 months and in 5 months), as well as photography workshops.
The long courses to become professional photographers allow you not only to master all the photographic techniques and its vocabulary (blurs, hyperfocus, sharpness zone, depth of field, backlighting, focal length, shutter release, autofocus, wide-angle, rule of thirds, etc.), but also all the stages of shooting and image processing.
Visiting the school allows you to discover the premises, the studios and the equipment, and is undoubtedly the best way to familiarize yourself with your future way of working. This is why, in addition to the open days, Spéos offers throughout the year personalized visits by appointment to come and discover the school with a member of the team.
Text and photos: Philippe Bachelier, teacher of Printing techniques at Spéos