Digital Photography—Understanding How Your Camera Reads the Light

Proper exposure is one of the keys to excellent digital photography. You can learn how to choose the right exposure for any particular shot, and then set ISO, aperture opening and shutter speed manually. You’ll find all the details in the five-part series of PhotographyTalk.com articles, starting with Digital Photography—Taming the Three-Headed Exposure Monster, Part 1. Most digital cameras, however, include a light meter that reads the light levels of a picture, and then automatically determines and selects the correct f-stop and shutter speed for a balanced image.

Virtually every digital photo you want to take has a slightly different light level, depending on the combination of light and dark areas in your image. Light also reflects from various surfaces, colors and textures differently. You can shoot portraits of two people in the same position in your composition with the same lighting conditions, but the light meter readings may result in separate exposure settings just because there is a subtle difference in how their skin reflects light.

Because of the variation of light in each of your photos, digital cameras have been designed to read that light with specific methods, or metering modes. Some are available on point-and-shoot cameras; all three can be found on most DSLR cameras.

Recommended Cameras:

Nikon D500 | Nikon D3300 | Canon EOS Rebel T5 | Sony A7RII | Canon 7D Mark II

Spot or Partial Metering

The light in the center spot of your framed picture is read and used to set the exposure. The light meter disregards readings from the area surrounding the exact center. A spot meter analyzes the light from only one to two percent of the entire image. A partial meter measures nine to ten percent.

Spot or partial metering can be very helpful when taking portraits or for macro digital photography. You want the primary subject or object correctly exposed, so it immediately draws the attention of viewers. You don’t need balanced light in the area surrounding the subject or object.

Typically, spot metering is most useful to a professional or experienced amateur. They are more likely to take specific kinds of digital photography (portraits, macro, etc.) that require spot metering. Plus, compact digital cameras don’t include this metering mode.

Center-Weighted Metering

Most digital cameras use this metering mode. It will set the proper exposure for virtually all of the candid and casual pictures that beginner photographers take. The meter reads the central area of the image where you’re primary subject or object will be and also evaluates the light levels of the surrounding space to select an average exposure.

Because this metering mode is “center-weighted,” your subject or object must be somewhere in the center for the meter to read it. Try to avoid shooting in a place where there is an extreme contrast between light and dark. This may confuse the center-weighted metering mode and result in poorly exposed digital photos.

Evaluative or Matrix Metering

Typically, you’ll only find this metering mode on DSLR cameras that include a number of metering choices. Evaluative metering is the most sophisticated technology. Not only does it take meter readings across your entire picture, but also searches a database of thousands of pictures and finds the one that best matches the kind of picture you’re taking. Your camera then uses the exposure data of that picture to set the exposure for yours. With so many types of digital photos in the database, it’s nearly a 100% certainty that there will be more than one that will match any kind of photo you may ever take.

Any of these automatic-metering modes makes digital photography more convenient and fun. If you want to grow as a photographer, however, then don’t always rely on your camera to read and select the correct exposure. Learn how to do it manually and try the alternative metering modes under different lighting conditions, even though your camera doesn’t agree.

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