A good straight talk about metering By Moni Caron

Controlling how much light reaches your camera sensor is an important decision for expressing your creativity. You know you have an idea in mind to take a picture, but can that idea be the end result if you don’t know how to meter light?

There is a difference in having a proper exposure and having the result of your creative mind printed on paper. You want more than just a picture that “turned out ok”? Then you need to understand metering modes, and understand how your camera “thinks”, what is the camera trying to tell you and what kind of information you need to give the camera.

So let’s take a look at metering modes and how they work, so you can select which one to use in different situations of light.

As cameras keep getting more and more sophisticated and more computer “thinking” is added to them, we have more precise ways of metering light. Today, we have , multi-pattern metering (called matrix or evaluative), center-weighted averaging metering, partial metering, and spot metering.

The metering system is nothing more than a microprocessor inside your camera, like a mini computer. In this processor, you have a big database of pictures and charts with information about those pictures so the camera can compare the light you have available and the settings in your camera to those stored pictures and suggest you the “proper“ exposure.

When you point the camera to a subject and half press the button, your exposure level indicator will show up in your viewfinder, where you see a number zero and some dots and/or sticks moving constantly to the left and to the right. As you point to different subjects, you see those sticks moving. They are trying to tell you if you have too much light or if you don’t have enough light, so that you can adjust your camera controls until you have a proper exposure, being “proper” an average exposure that reads ZERO in those “sticks, numbers and dots of your viewfinder, or a bar that stays green UNDER the ZERO mark.

Your goal for proper exposure is to get those dots and sticks in the zero mark. When it is in the zero mark, your camera understands that for an average scene, the colors will turn out right, and you will have good light for the scene. That is known for what the camera considers 18% gray, that is, the camera averages all the tonal values (the brightness levels of everything in shade, in sun, all the colors in the scene, etc) and translates that into an “average” amount of light, that is set by the manufacturer as the “proper” exposure level as 18% gray. Once your metering system is under the zero in your camera, it is like the “correct” exposure will bring out all the colors right: red will be red and not pink, yellow will be yellow and not orange, and all the other colors should be right.

Don’t get too confused with 18% gray. It is just a number so you understand how the camera “thinks”. It will not show up on your camera in any place. It is mere information so you can look it up online for more detailed information of how camera understands colors and tonal values.

Now, have in mind that not all situations of light will have colors, brightness and contrast turn out all good all the time. The camera microprocessor will interpret the light in 3 different ways, depending on the metering system that you pick.


Multi pattern, or evaluative, or matrix metering system (the multi pattern gets different names with different camera manufacturers) - this system divide the overall scene in little pieces and assigns each piece a brightness value. Then it takes in consideration the lens you are using, the ISO, the aperture, and the shutter speed you have set in your camera and compares all these with the database stored in the microprocessor until it finds a stored situation of light that is similar. Then, it will suggest a metering “solution” by blinking in your viewfinder in the left side or in the right side of the zero, meaning you need to adjust the exposure by changing your shutter speed or your aperture until your metering bar is in zero. This system is great when the light is coming from behind you and when you have lots of colors in the scene. A general purpose metering mode. Good for portraits and street photography with tricky light, it will give you accuracy and proper exposure about 80% of the time.


Center-weighted averaging metering system - a system that interprets light by giving “weight, to some part of the scene more than others. So the camera reads the light from all parts of the scene and assigns 70% of the light from the center of the frame and 30% of the light from the edges (numbers that can also be 60% to the center and 40% to the edges, 75% to the center and 25% to the edges, 80% to the center and 20% to the edges, depending on the manufacturer preset. What it means is that it will average a reading considering that whatever is inside the center of the frame is more important than the other outside of the center of the frame. This metering system is better for contrasty situations of light, backlight and pictures in which white or black subjects are NOT in the center of your picture. If white or black are in the center, your chances of having an overexposed or underexposed pictures will increase dramatically, since the camera is trying to turn everything “gray” for average good color rendition. Also great for side lighting when you have lots of shadows in the scene, as an end of the day street picture.

Partial metering system - a system that interprets light assigning 6.5%, 9% or 10% of your viewfinder area at the center as important for the metering results, depending on the model of the camera. That means once you have picked your CENTRAL point of focus (let’s say you are pointing to the eye of your model to meter light), the camera will consider the area between 6.5 to 10% around it to “suggest” you the “proper” exposure, ignoring everything else in the scene for metering purposes. That means it would not matter if you are photographing someone with very light skin with a black wall behind: the camera will only read the light off the eye (and around the assigned area from 6.5 to 10%, depending on your camera) to give you the 18% grey “proper” exposure. A great system to pick if you have a lot of backlighting much brighter than your subject in the foreground. The meter won’t be fooled by lighter or darker scenes around your subject with this system. It is mostly center weighted. It will meter off the CENTER point of focus, so you may need to recompose your scene after you lock exposure to take the picture.


Spot metering system - a very precise metering mode. In Canon systems that could be approximately 3.8% CENTER, ignoring everything else in the metering. Your metering needs to use the CENTER focus point to meter off the scene, then you lock exposure and recompose the picture using whatever focus point - or manual focus- you want to select, but keeping the original metering from your CENTER focus point. The spot metering is great for when you photograph bright colors or when you want very specific metering ignoring almost all the rest of your composition. That means if you are photographing a person against the window (with bright sun behind the person) and you spot meter the person using your CENTER focus point in the eye of the person, you will have a metering for exposing to the face. Then you lock your exposure in that metering- meaning you don’t change your aperture or shutter speed - and recompose the scene with another auto focus point or manual focus and take the picture. The background (the light behind the person) will be blown out much brighter than the person. If that is the effect you want, SPOT METERING is great for this situation. Spot metering requires that you really understand the metering and know exactly what end result you want, often meaning you need to adjust/compensate the exposure toe the brighter or darker side, depending on the result you want from the picture.

When picking which metering system to use, take into consideration the situation of light you are at: low light, side light, front light, backlight. Also, pay attention if there is a very large area of the frame filled with darker tonal values.

When you have snow, you need to compensate your exposure to the PLUS side, meaning you need to overexpose your scene at least one F/stop or your snow will be dark grey. It happens because when you are metering a person in snow, the metering system is seeing all the snow around the subject and “thinking” “it is too bright!”, hence suggesting you need to adjust to a darker exposure. But you know the camera is trying to make everything 18% gray, so you need to overexpose the metering to turn snow white, and not gray. So every time you have lots of white in a scene, use your “suspicious” meter and adjust your exposure to the PLUS side, unless you don’t care about the large white part of the scene being darker than it looks.

The same thinking applies to dark colors being most of your frame: you need to compensate the exposure to the MINUS side, so you don’t have your blacks being too light. Black is DARKER than gray, so you need to UNDEREXPOSE at least ONE f/stop for a correct exposure for darker tones.

Hope this metering talk guides you towards better pictures.