11 Dec 2016

Photography Experiment: Metering Modes Don't Generally Matter

Cameras have different metering modes that let them decide how much to expose the photo, in other words, how bright or dark to make the scene. If you wondering why that's needed, keep in mind that there's a huge variation in brightness of scenes, so, like the eye compensates by narrowing or widening your pupil, the camera needs to as well [1].

Cameras generally have three common metering modes — matrix, center-weighted average and spot. These use different algorithms, causing the same scene to end up brighter or darker. Spot is the simplest to explain — the camera pays attention only to the center of the screen, ignoring everything else in the photo. This makes sense if there's one central subject in the scene you care the most about, like maybe the moon in a night scene. Center-weighted average is a more flexible version of spot where, instead of ignoring everything outside the spot, the camera gives it less weightage, 20-40%,  reserving 60-80% for the center. Matrix is the default mode, and the most sophisticated — the camera measures a number of zones, and combines the measurement from those zones, taking into account distance to the camera, autofocus point, whether a point is in focus or blurry, colors and so on.

That's the theory. Do these modes generally make a difference in practice? To find out, I experimented with all three modes. I chose a night scene, because night scenes are generally harder for cameras to handle. Further, I chose one with a significant difference in light levels — the bottom part is very dark, and the rest, including the sky, is moderately lit. Here's a photo with matrix metering:

With center-weighted average metering:

And with spot metering:

Right-click each photo and open in a new tab to compare them.

There's little difference between these three photos. Even the slight differences you see can just as well be adjusted later. You don't need to worry about using the right metering mode for this scene.

But maybe other scenes will perform differently? To find out, I chose another scene, which is also a night scene, but different from the first in that the bright parts are much brighter and closer. Here's the photo with matrix metering:

Center-weighted average:

And spot:

This time, there's a bigger difference: center-weighted average and spot are much brighter than matrix. But again, this is only a difference in exposure between 1/5 and 1/2 second. That's only 1.3 stops — you can easily compensate for that in post, either up or down, given the dynamic range of this camera. It's not a smartphone.

The conclusion is that metering modes don't matter most of the time. If you have a specific situation, like capturing the moon in a nightscape without blowing out the moon, you may want to use a specific metering mode but, most of the time, it doesn't matter.

[1] Metering modes are different from focus modes, which decide whether you're more interested in a nearby or a distant object. This experiment covers metering modes, not focus modes.

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