Understanding Exposure in Photography - Tip 1: How Meters Work

Exposure


The correct exposure is essential to the quality of your image.

Some people follow the philosophy "Fix it in the computer." But that should be the last resort. Fixing a photo on the computer is not the magical answer that it has been made out to be. In fact, every tonal adjustment you make to your photo on the computer, making it lighter or darker, etc., reduces the amount of pixel data in your photo. So as you're "saving" your image, you're actually degrading it, throwing away data. Best to get it right in camera.



Meters

The meter in your camera measures the light in your scene telling you or your camera what shutter speed and aperture settings will provide the proper exposure.

It's important to know how the meter sees and what it is trying to do. A meter takes in all of the tones in the scene (light and dark) and averages those tones to compute an exposure setting. The meter is finding an average, aiming for an 18% gray tone. And that's great for most scenes, where light and dark tones average into gray, such as the photo below.

photography and grey tones


Types of Metering

Advances in camera metering systems over the years have been impressive. Still, it's important to know what your meter is thinking and how various meters see the light.

Most cameras will read the light in the scene by measuring the brightness of light reflected through the lens. For more accurate light readings, handheld meters can tell you how bright the ambient light is in any environment. Here is a quick breakdown of typical modern metering options:

Matrix or Evaluative Metering — This type of metering breaks the scene up into multiple segments which are analyzed for brightness and then compared to a pre-programmed database of thousands of typical photographic scenes. All of this happens instantaneously. Matrix/Evaluative metering modes are very accurate and useful especially in situations where you're using an auto-exposure mode or when the light is changing frequently. While not perfect, they come close in most situations.

Spot Metering — Spot meters read the brightness of a single spot in the middle of the frame, allowing you to take a precise reading of a small area. Spot metering is very handy when you're shooting in manual modes and have the time for extreme precision.

Incident Metering — Handheld meters provide highly accurate light measurements by metering the ambient light in a scene. That is, they tell you exactly what settings to use on your camera by telling you exactly how bright it is. There are drawbacks to using a handheld meter, including the cost of the meter. And for an accurate reading, the meter has to be in the same light as your subject. This can be problematic in a situation like a concert, where access to the stage is often controlled.

Latitude

Correct exposure settings are essential for serious photography. While your eyes are capable of seeing detail over a wide latitude, film and digital cameras have a much tighter latitude. If you expose for the sunlight, things in the shade will appear dark. If you expose for the shade, everything in the sunlight will be too bright. There are techniques to balance the light in such situations, such as using fill-flash.

But it bears repeating: Setting the correct exposure is essential to the quality of your image.