Metering & Exposure Compensation

Every exposure mode you learned last week — Program, Aperture, Shutter, even the meter inside Manual — leans on one quiet judge: the light meter. It looks at your scene and decides what a "correct" exposure is, and it's right most of the time. But it makes a single sweeping assumption about the world, and when a scene breaks that assumption, the meter confidently gets it wrong. This week we learn how it thinks, the modes that change what it measures, and the one button that lets you overrule it without leaving your shooting mode.

How the Meter Thinks (and Why It's Fooled)

Your camera's meter assumes that, on average, the world is a medium tone — a mid-gray, often called 18% gray, the rough average of a typical scene. So it sets exposure to make whatever it's pointed at come out as that middle tone. Point it at an average street and it nails it. But point it at a snowfield, and the meter — trying to turn all that white into mid-gray — darkens the shot, and your snow comes out dingy and gray. Point it at a black cat filling the frame, and the meter brightens everything, trying to lift that black to gray, and now your cat is a washed-out smudge. The meter isn't broken. Its one assumption just fails whenever the scene is genuinely much brighter or much darker than average.

Metering Modes: What the Camera Looks At

You can change where the meter looks. Three modes cover almost everything:

• Evaluative / Matrix (sometimes Multi) — the camera reads the whole frame in zones and makes a smart, scene-aware guess. The best default; it's right a remarkable amount of the time.
• Center-weighted — the meter pays most attention to the middle of the frame and feathers out from there. Predictable and old-school; good when your subject is central.
• Spot — the meter reads only a tiny circle, often just the center focus point. Surgical: meter off the one tone you care about — a face in harsh light, a gray card, the moon — and ignore everything else.

Start in evaluative for general shooting, and reach for spot when the light is tricky and you know exactly which tone must be right.

Exposure Compensation: The One-Click Override

Here's the fix for the fooled meter, and it's a single button — usually marked +/−. Exposure compensation tells the camera, "whatever you think correct is, make it this much brighter or darker." It works in the semi-automatic modes — Program, Aperture-preferred, Shutter-preferred — by shifting the target the meter aims for.

• Bright scene fooling the meter dark (snow, a white wall, a beach) → dial in positive compensation, +1 or +2, to put the white back to white.
• Dark scene fooling the meter bright (a black backdrop, a dim theater, a shadowed subject) → dial in negative compensation, around −1, to let the dark stay dark.

The counterintuitive part worth memorizing: to photograph something white, you often add light; to photograph something black, you often subtract it. In full Manual you're already setting exposure yourself, so you "compensate" simply by choosing your settings against the meter scale — or, if you're running Manual with Auto ISO, the compensation button rides the ISO instead.

How Metering Works Across Cameras

The meter makes the same assumption everywhere — but whether you can see it being fooled before the shot is the dividing line.

"I photographed a snowman and the camera turned the snow into wet cement. One press of the plus button and it was snow again. I've been lied to by my camera for years and didn't even know it."

Alexandra