Camera meters
Repeat after me: “I am smarter than my camera’s meter; I am smarter than my camera’s meter”. Repeat until you believe. Go ahead, it’s fun. And it’s true too—well, for most of us anyway.
Despite what your camera’s manual states, the meters in our cameras are not perfect. You see, your meter is just a measuring device, just as a thermometer is. Think about the thermostat in your house. If you set it to 70 degrees, the heat will stay on until the thermometer (the measuring device) in the thermostat, indicates 70 degrees, then the thermostat shuts off the heat.
Your camera meter serves a similar purpose as the thermometer; it can tell you when your chosen settings will allow enough light on your film or camera’s sensor.
The meter in your camera measures light reflecting from your subject and is called, logically enough, a reflective meter. Camera makers calibrate meters so that when the meter is “zeroed”, or showing “correct” exposure, whatever you point your meter at will be rendered as if the subject was of average brightness, or what is referred to at 18% reflectance. 18% reflectance means that 18% of the light striking the subject is reflected, the rest is absorbed. 18% reflectance is neither light nor dark, it’s right in the middle. We also refer to this as medium or middle toned.
Now, since many scenes in the world will average out to, well, average reflectance, going by what the camera meter indicates as correct will often work just fine. However, not all scenes or subjects are medium toned (18% reflectance) and you’ll need to know when to take command of your meter. We’ll get to all that in future lessons.
If your subject, let’s say a snow bank, reflects more than 18% of the light striking it, the meter doesn’t know that and assumes that the snow is a medium toned blob of stuff. We know it’s not. If you take the picture at the “correct” meter reading, the snow will come out as a medium gray mush. If you simply use the "zeroed" meter reading, your images will come out “averaged”. If your scene or subject is average in tonality, then things will be fine. But if they’re not, then things won’t come out the way you wanted.
Most cameras have an indicator in the viewfinder that displays metering information. It’s usually a scale with “0” in the middle and + and – on either side. If the meter indicator is on the plus side, this means the subject will come out lighter than medium. If the meter is on the minus side, then you’ll get a subject that’s darker than medium.
For now, just know that every in-camera meter measures light assuming that the subject reflects 18% of the light. We know that not all subjects will reflect 18% and I’ll address that in the next lesson.
Exposure modes
You’ll notice that your camera has several exposure modes and several metering modes. Here’s a brief description of each. As always, get out your manual and follow along as different camera makers may use different names for these modes.
- Manual: You set the shutter speed and aperture
Automatic modes:
- Aperture Priority: You set the aperture; the camera sets the shutter speed
- Shutter Priority: You set the shutter and the camera sets the aperture.
- Program: the camera does everything
Metering modes
Metering mode is different from exposure mode. Metering mode defines how your meter measures the light in a scene.
- Spot metering: Typically, your camera will have a spot metering mode, which uses only a small portion of the viewfinder to sample the scene. In many cameras you can choose among several “spots”.
- Center weighted metering: This means that the camera takes most of the exposure reading from the middle part of the scene, usually defined by a large circle in the viewfinder. The rest of the reading comes from areas outside that middle zone. Usually, about 75% of the exposure reading is from the circle area.
- Matrix or evaluative metering: Here, the viewfinder is divided into segments, or a matrix. The camera evaluates each segment and compares brightness values. Using a proprietary algorithm, the camera uses this information to determine an exposure.