A light meter reading is a small scale in your viewfinder or on your screen that shows whether your current settings will make the picture darker or brighter than the meter thinks it should be. A reading of zero means the meter is satisfied; plus means brighter, minus means darker. It is a guide, not a command.
What the scale is telling you
The scale is measured in stops. One stop up doubles the light reaching the sensor, and one stop down halves it. Marks between whole numbers are usually thirds of a stop. If the needle or bar sits at plus two, the meter expects the image to be two stops brighter than a middle gray scene.
That phrase matters. Meters assume the scene averages out to a medium gray. A snowy field or a dark room does not, so the meter can be fooled.
Step by step: use the meter in manual mode
- Set your aperture for the depth of field you want.
- Set a shutter speed that suits the movement in the scene.
- Choose a sensitivity value appropriate for the light.
- Half-press the shutter button to wake the meter.
- Read the scale, then change shutter speed, aperture or sensitivity until the mark reaches zero.
- Take a shot and check the screen and histogram.
Choose the metering mode
The mode decides which part of the frame the meter listens to.
| Mode | What it measures | Good for |
|---|---|---|
| Evaluative or matrix | The whole frame, weighted by pattern | General shooting |
| Center-weighted | Mostly the middle area | Portraits, steady scenes |
| Spot | A tiny circle | Backlit subjects, stage lights |
When to ignore zero
Zero is right for average scenes, but not for every scene. Use these rules of thumb and confirm on the histogram:
- Bright snow, sand or white walls: move the reading about one to two stops toward plus, or the result looks gray.
- Black cloth or a night street: move toward minus, or the dark areas look washed out.
- Strong backlight: spot meter the face, then set that reading to zero.
Exposure compensation does this adjustment for you in the priority modes. Dial plus or minus and the camera shifts its choice by that many stops.
FAQ
Why does my meter say zero but the photo looks dark?
The scene is probably brighter than average, or the screen brightness is low. Check the histogram; if it bunches against the left edge, raise exposure toward plus.
Is a handheld meter better than the one in the camera?
A handheld meter reads the light falling on the subject, so color and tone of the subject do not fool it. A camera meter reads reflected light. Both give good results once you learn their habits.
The Short Version
Zero on the scale means a middle gray result. Choose a metering mode that fits the scene, set zero or close to it, then shift toward plus for bright scenes and minus for dark ones, guided by the histogram.