Metering & the histogram
Metering modes, reading the histogram, exposure compensation, zebras, and exposing for the highlights.
- Explain how the camera meters and where it gets fooled
- Read a histogram to judge exposure objectively
- Use zebras and exposure compensation to protect highlights
The meter is the camera’s opinion about brightness. It is usually right and occasionally very wrong, so you need a way to check its work — and that is what the histogram and zebras are for.
How metering works, and fails
Metering measures the light and aims for a middle grey. Multi metering reads the whole frame and is your sensible default; center-weighted and spot concentrate on the middle or a single point for tricky subjects. All of them are fooled by the same thing: a scene that is not, on average, middle grey. Point at snow and the meter darkens it to grey; point at a black cat and it brightens it. Knowing how it fails is what lets you correct it.
The histogram tells the truth
The histogram is a graph of tones from black on the left to white on the right. It cannot be fooled by your eyes adjusting or by a bright screen. Read it simply:
- Data piled against the right edge means blown highlights — detail lost.
- Data crushed against the left edge means blocked shadows — also lost.
- A well-spread graph that touches neither edge hard is usually a healthy exposure.
There is no single “correct” shape — a night scene should sit left — but the edges never lie about what you are throwing away.
Zebras: highlights, live
Zebras overlay animated stripes on areas approaching clipping, right in the live view. Set to a high threshold, they flag exactly where the highlights are about to blow while you still have time to pull back. For stills they are an early-warning system; for video, where you cannot recover highlights in a RAW file, they are essential.
Expose for the highlights
When a scene has more contrast than the sensor can hold, choose what to protect. The reliable habit is expose for the highlights: set exposure so the bright areas keep their detail, then lift the shadows later if you shot RAW. Recovered shadows carry some noise; blown highlights carry nothing at all. When in doubt, protect the brights and use exposure compensation — usually a touch negative — to keep them.
In the field
Photograph a bright sky over a darker landscape. Expose once so the land looks right and check the histogram — the sky is probably clipped. Now dial exposure compensation down until the zebras leave the sky, and lift the land in editing. Compare. Protecting the highlights wins.