The meter inside your DSLR measures the amount of light reflecting from your scene. It’s an invaluable, although not infallible, photography tool. Here’s a short explanation for the most common in camera light meters on DSLRs.
Types of In Camera Meters
Multi-zone Metering / Evaluative Metering / Matrix Metering / (Default setting)
This meter mode takes readings from a variety of points throughout your viewfinder (imagine a grid) and averages them to guess the best settings. It’s often the default setting in DSLRs, regardless of the manufacturer. What does vary greatly from manufacturer to manufacturer, and even model to model, is the number of points the meter evaluates and the calculation for combining all the readings to get one exposure recommendation.
On this setting, the camera meters from a very small point in the viewfinder – not more than 5% of the entire scene.
Similar to Spot Metering, the main difference with Partial Metering is that it measures a larger area of the viewfinder (as much as 15% of the scene).
Center Weighted Metering
The middle of the viewfinder gets top priority in this mode, with less sensitivity granted in the edges of the frame.
The entire scene is metered and weighed equally in the calculation to determine exposure.
So, now that you’ve had the crash course in meter types, the best thing to do is get out there and shoot with them all. There is no ‘best’ choice, or easy answer. I won’t tell you which camera meter to use. On the contrary, I will tell you to use ALL of your meters until you get a feel for which one works best for each situation. Before you start shooting, though, it is important to know how a camera meter works. This post assumes basic exposure knowledge. If you’re not familiar with shutter speeds, f-stops and ISOs, I recommend reading through the exposure basics series, first.
18 % Grey
Camera meters are color blind. They see everything in shades of grey – from black to white and every shade in between. Halfway between white and black is middle grey. Middle grey reflects 18% of light; this is why it’s called 18% grey. Camera meters are calibrated to 18% grey. Meaning, regardless of the type of metering, the meter will give a reading designed to photograph at 18% grey.
Have you ever taken a picture of snow, using your camera’s meter (or automatic mode) and the snow came out grey – not the pristine white you were expecting? That’s because your camera meter wants everything to be 18% grey – even the brightest white and the darkest black.
Let’s look at an example:
First, I photographed three solid colored cards, using my in camera Spot Meter. On the left, I had a black card. In the center, I had an 18% grey card. And, finally, on the right, I had a white card. I took a picture with the Spot Meter aimed at the 18% grey card in the middle. As you can see below, I have black, grey and white in my picture. This image is perfectly exposed.
Next, I rearranged the cards so that the Black card was in the middle, where my meter was aimed. As you can see, my black is no longer black – it’s much brighter. This image is overexposed. When too much light enters the camera, it causes overexposure. In this scenario, the meter measured that more light was required to make the metered area 18% grey (to turn black into grey). As a result of the extra light, my grey card went white.
Lastly, I put the white card in the middle. Since the camera meter measured that less light was needed to photograph the metered area as 18% grey, less light was used to take the photo. My white card went grey, my grey card went black. This image is underexposed because not enough light entered the camera to photograph the white as white. To correct this, allow more light to enter your camera by adjusting your shutter speed, f-stop or ISO.
What does this tell us about Metering and Exposure in photography?
An easy way to ensure a perfect exposure, is to carry an 18% grey card with you. Take a meter reading off the grey card in every scene. Then, set your exposure and remove the card before you take your photo.
Don’t have a grey card with you?
If the scene is dark, the camera meter will turn it grey by overexposing the image. To preserve the dark, underexpose the image. To underexpose, decrease the amount of light entering your camera. Refer to the Exposure Basic’s Series for more information.
If the scene is light, the camera will underexpose it, turning your whites into greys. To preserve the whites, overexpose the image. To overexpose, increase the amount of light entering your camera. Refer to the Exposure Basic’s Series for more information.
The next time you’re photographing snow, try overexposing by as much as 2 – stops. As always, bracket your exposures for best results.