Guide to the Light Meter and Exposure Modes in Photography

Explore the use of the light meter and the various exposure modes to enhance the quality of your photographs.

Author: Marco Crupi

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This article is a segment of the Digital Photography Course. Click here to return to the main course overview.

Incident Light Meter.

The light meter, a fundamental device in photography, can be integrated into the camera (internal light meter) or used as a separate unit (external light meter). Its primary function is to measure the amount of light needed to achieve correct exposure. This is done by recommending an appropriate combination of exposure time and aperture, in relation to the set ISO sensitivity.

Light meters are mainly classified into two categories:

  • Reflected Light Meters: These are typically built into cameras. They work by pointing the camera towards the subject; the meter measures the light that is reflected from the subject back to the camera. It’s a particularly effective measurement in scenarios where the light is evenly distributed.
  • Incident Light Meters: These are usually external meters, preferred in controlled environments like photographic studios. They are positioned near the subject, with the white hemisphere facing towards the camera. They are ideal for high contrast situations. In such cases, the meter can be pointed directly at the light source and calculate an average between this reading and that of the shadow areas, for optimal exposure balance.

Moreover, the integrated light meter in a camera can operate in different modes, each suited to specific light conditions and to achieve particular atmospheric effects. Choosing the correct exposure mode is crucial for capturing the desired image, influencing factors such as depth of field, motion sharpness, and overall light balance in the image. Understanding and mastering these modes are therefore essential for every photographer aspiring to create technically accurate and artistically expressive images.

Exposure Modes for Various Camera Manufacturers.

  • Matrix / Evaluative Metering: this mode, standard in digital SLRs, divides the scene into multiple zones, similar to chessboard cells. Each cell is individually analyzed for light, and then, through a specific algorithm of each manufacturer, an average exposure value is calculated. This system uses pre-set scenarios stored in the camera, making it the most sophisticated and reliable method currently available.
  • Center-Weighted Metering: this mode gives more weight to the central portion of the frame, assuming the presence of the main subject in that area. Although once very popular, it is gradually being replaced by Evaluative and Partial modes, which generally offer superior results. It is particularly suitable for portraits, thanks to its ability to effectively interpret skin tones, provided the subject is positioned in the center of the frame.
  • Partial Metering: this mode focuses on a limited area in the center of the frame, assigning it greater importance in light measurement. The size of this area varies depending on the camera but is generally between 8% and 10% of the total area. It is particularly useful for foreground subjects against bright backgrounds or in backlight conditions. Offering a wider field of action than Spot mode, it is more complex for beginner photographers.
  • Spot Metering: in this mode, the focus is on a small area at the center of the frame, usually about 2-3% of the total area. The meter provides appropriate time and aperture values only for that specific area, ignoring the rest of the scene. It is ideal for situations with strong light contrasts, such as in theater performances or backlit conditions, as it allows for precise exposure measurement on the subject without being influenced by surrounding light. It is an effective mode, but requires some skill in use.
  • Multi-Spot Metering: this is an evolution of the Spot mode. It is used when the scene presents brightness variations. Instead of relying on the Multi-zone system, the photographer can manually select areas of interest, and the camera calculates the mathematical average to determine the correct exposure. This mode offers greater control and allows for more precise management of complex lighting scenarios.
  • Highlight-Weighted Metering: many cameras also have a measurement mode with high-lights priority, which has an indicator icon similar to that of spot measurement, but with a star next to it. The highlight priority metering mode more effectively protects the brightest areas in your shots. This can be very useful if you have some brighter areas near your subject that you do not want to overexpose. On the other hand, the high-lights priority can be too aggressive in certain scenes. If there are bright but unimportant scenes in your shot, or parts that you will cut out later, then the high-lights priority will certainly underexpose the important parts of your composition.
  • Entire Screen Average Metering: this exposure meter mode measures the average exposure across the entire screen and sets the camera’s exposure to the appropriate level. This exposure level will remain stable even if the composition or the subject’s position changes.

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