Originally published in Craftsy Photography Blog, October 2015
Every modern DSLR comes with what is known as metering, which is how the camera determines the shutter speed and aperture, based on lighting conditions and selected ISO. The integrated light meter within these DSLRs automatically measures reflected light and uses this information to determine proper exposure. As there are various lighting situations, there are a number of metering modes to try to address them. The most common metering modes are Matrix (Nikon) or Evaluative (Canon) Metering, Center-weighted Metering, and Spot Metering. So what are they and when should you use them?
Camera meters work best when scenes are evenly lit, though this is not always the case when you are shooting. Matrix or Evaluative Metering mode works by dividing the entire frame into multiple regions, which are then analyzed on an individual basis for light and dark tones. The number of regions the frame is divided into varies by camera. In addition, there is one more element that influences this type of metering—the focus point. After gathering information from all the individual regions, the metering system factors in where you focused within the frame and marks this region as more important than all others. A sort of weighted average is then computed.
I will admit that this is the metering mode that I use most often, as it is very good at determining a proper exposure, especially in landscape and studio photography. I shoot with a Nikon, which has the added bonus when using this mode of comparing image data to a database of thousands of pictures with various lighting conditions to help with exposure calculation. A quick look at the histogram can confirm the exposure and adjustments, such as aperture or exposure compensation, can be used to fine-tune the exposure, if needed.
While Matrix Metering is very useful, it is not always the ideal choice. For instance, if you are photographing a person or object that is backlit, then you would be better served with using a different metering mode as the bright background may cause Matrix Metering to factor in too much brightness, underexposing your subject. Center-weighted Metering evaluates the light in the middle of the frame and its immediate surroundings, ignoring everything else. It also ignores your focus point and only makes its calculation based on the center of the frame. Some cameras will also let you adjust the diameter of the center region being measured, which is often a menu selection.
This is a good option then if your focus point is in the center of the frame. I use this metering mode when shooting close-up portraits that are backlit, as the face will be properly exposed, though the background may be overexposed as it was ignored in the camera’s computations. If you shoot RAW, you can regain some of the background detail when processing your photos. To me, what is most important in this situation is proper exposure of the face. I also use this mode when shooting close-up portraits on a dark or black background for similar reasons.
Suppose you have a backlit situation or a situation when the exposure of the focus point is most important but the focus point is not in the center? This is where Spot Metering comes in. Spot Metering only measures the light around your focus point and skips everything else. It evaluates this single region and computes exposure based on this region only.
If you are photographing a figure that is backlit but not in the center of the frame, then this would be a good mode as the other modes could result in an underexposed or even silhouetted figure. This is also a good choice for wildlife photography, where you want to ensure proper exposure of the animal, which may not be centered and could be moving among lighter and darker backgrounds. In general, Spot Metering works best in situations where your subject is much lighter or much darker than its surroundings.
Changing Metering Modes
This varies by make and model, so I would suggest checking your manual or looking it up online. Sometimes it involves a menu selection, other times it is a button combination on the camera body. There are also other metering modes available on some camera models, such as multi-spot and partial metering, so explore your camera to see what is available. Note that you cannot change the metering mode if shooting in Auto or in a Scene mode. You can, however, change meter modes when shooting in Manual, Aperture Priority, Shutter Priority, or Program Mode, though changing meter modes in Manual will have no affect as the camera is not computing anything.
Also, keep in mind that metering modes can be used creatively. For instance, as mentioned above, shooting an off-center backlit subject can result in a silhouette when not using Spot Metering mode, which may be exactly what you want.