Photography is the documentation of light. Documentation of light requires proper exposure of your shot. To achieve the proper exposure, one needs to meter the subject effectively. Thanks to technology, long gone are the days where a photographer is required to use an external light meter, apply some math and possibly some guesswork. The advent of in-camera metering and the improvement of lens technology has made the world of photography much easier for the hobby photographer.
Understanding how your camera’s metering system works will make a dramatic difference in you photography. There are generally three types of metering methods: Average Metering, Center Weighted Metering and Spot Metering. Knowing the advantages and disadvantages of each is important as a photographer. It will help you set up your shot properly and get the best exposure. Below is a break-down of each.
Basic In-Camera Metering Methods
[singlepic=165,320,240,,right] By default, most cameras, especially consumer models, will use Average Metering. The camera evaluates the light of the full frame of view and determines an average light reading. The camera then adjusts your aperture or film speed (depending on which shooting mode you are in) to achieve the best exposure. Modern cameras utilize a more advanced averaging method called multi-zone metering which also takes into consideration coloring, white balance settings and so forth. While the exact methods behind multi-zone metering varies between manufacturers, it is safe to assume that it is, in general, more advanced and more accurate than the traditional average metering. Regardless of how the light levels are determined in average metering, this type of metering is going to be ideal for beginners. Once comfortable with the camera, many advanced photographers stray from average metering as it does not give the photographer any amount of control over the exposure (without using exposure compensation). The major disadvantage of this type of metering is that your camera will try to determine an exposure based on every object in the frame. Except in rare conditions, it is unlikely that every object will be the subject of your photograph, and the subject may be overexposed or underexposed depending, especially when the subject contrasts greatly with other objects in the frame. While there is always the argument, especially in the digital world, that compensation can be applied at developing time, it is still always better for your shots to be optimized at shutter time. Unfortunately for you point-and-shoot camera owners, this may be the only metering method available to you.
The photograph at right is the result of average metering. As you can see, everything in the background seems to be metered pretty well. The figure, since it only takes up a portion of the scene, isn’t exposed very well. This is an extreme situation where the back-light isn’t ideal for average metering. But you get the idea of how it works.
[singlepic=166,320,240,,right] Most of the time, advanced photographers may prefer center-weighted metering. In this type of metering method, your camera will still evaluate the light levels from the entire frame, but it will place much more weight on the “center” of the frame. This yields a photograph where the focal point is much more ideally exposed while still giving some compensation for the other objects within the frame. It is important to know that despite being called center-weighted, the “center” is often determined by the focusing point that you set in your camera. For example, my camera has eleven focusing points that I can select. If I move the focusing point to the right, all focusing and metering is now based on that point, despite the namesake. Under normal circumstances, this is the ideal metering method. You get a nice balance across the frame, and your exposure will usually be pretty good. However, it is not the solution to every scenario, and you will need to learn when not to trust center-weighted metering. Many inexperienced photographers discover this mode and use it religiously expecting perfect results every time. They are often greatly disappointed when they get back to their darkroom or their computer.
As you can see in the example picture to the right, as compared to the average-weighted photograph from above, there is a bit more detail of the face and the background is starting to become over-exposed. While this isn’t the ideal exposure for the figurine, yet, there is no longer a doubt about the actual focus of the image.
[singlepic=167,320,240,,right] Like center-weighted metering, spot metering allows control over the metering point. Unlike center-weighted metering, spot metering only takes the subject into consideration when determining exposure. This is incredibly useful when you have a back-lit subject or one that is significantly brighter than the surrounding scene. There are some side effects to spot metering such as the over-exposure or under-exposure of everything except the subject. In many cases, this is the desired effect and spot metering is appropriate as a solution for this. But sometimes, when the context is important, spot metering will not likely yield the results you’re looking for.
This example photograph is much closer to the ideal exposure considering the subject and its surroundings. As compared to the photographs above, this gives you the best detail of the figurine’s face. However, the edge definition is lost slightly because of the back-lighting. Ideally, I would want to use exposure compensation to give myself a slightly lesser exposure. I would lose a slight amount of detail in the face, but the edge condition would be much more idea.
Advanced Exposure Control
More experienced photographers will learn when and when not to trust their camera’s in-camera meter. Depending on your camera, you may be able to manually pre-set a meter level. This is ideal when you have the time to set up a shot. Many photographers will meter off of a known value, such as a white balancing card or a white shirt, at the start of their photography sessions. This is especially useful in controlled environments such as a studio. Bracketing is also a feature that many cameras support. Bracketing is when your camera takes a small set of photographs in succession, each with different shutter speeds, so that you can later merge them in the studio. Even if your camera doesn’t support this, you can bracket some photos by manually tweaking the shutter speeds between shots. A tripod is recommended. Later, in your photo editor, you can merge the images to create the best exposure for the entire scene. The details of these advanced methods are best saved as a topic for another day.
Metering is one aspect of your learning curve that will set you well above the average photographer. The best photographs aren’t worth the paper they’re printed on if the exposure isn’t perfect. The best and simplest tool that you have is your in-camera meter. You owe it to yourself and your hobby to learn how to use it well.