How-To: Getting the Right Exposure
How-To: Getting the Right Exposure
Text and Photos by Lynne Eodice
One of the most important issues you should address before shooting a picture is setting the exposure. First of all, a good exposure is one that captures the overall tonal range (the range of dark through light tones) that is visible to you before you click the shutter. What you’re trying to do is to capture an image that shows light tones, dark tones and everything in between. When you create a good exposure, it means that you’re giving your camera’s sensor the right amount of light to record your subject’s tones correctly.
Put quite simply, good exposure is the amount of light that it takes to record a scene correctly onto your camera’s sensor. If you give the sensor too much light, your picture will be overexposed. The image may appear washed out and lacking in detail in the brightest areas. If there’s too little light, the image will be underexposed and will look dark and dingy. So in most cases, you’ll want to capture an image that’s neither too dark nor too bright, but just right.
Some subjects are easy to expose correctly. When a scene is well lit and has an average tonal range (with nothing being too dark or too light) and the light is fairly even, getting a good exposure is a pretty simple process. Your camera’s built-in automatic exposure does a good job of recording subjects like this correctly. But the more complex your subject is in terms of light and dark tones, the more challenging proper exposure can become. For example, you need to know how your camera’s meter will react to a beautiful snow-covered landscape—and what you need to do to record that snow the right way.
You’ve probably heard this terminology relative to photography, but what does it really mean? Here’s the lowdown: All in-camera metering systems are designed to read tones in a scene as 18-percent gray (or a medium gray value). The reason for this is that this tone is midway between pure black and pure white. And it doesn’t matter what color your subject is or what lighting illuminates it—your meter will usually give you a recommended exposure that records your subject as a medium tone.
When you photograph a predominately white or black subject, the white may turn out darker and the black may be lighter. This is because your camera wants to expose them as medium gray. A black horse may appear to be gray, while a beautiful snow scene may also appear gray. By finding an actual mid tone in a scene that you want to shoot and reading it correctly in an image, you’ll establish the exposure for all the other tones in that scene. By establishing this tone as the middle range, the brighter areas will record as whites and the darker areas will record as dark grays and black. The reason this works so well is because the objects in a scene are of different values and won’t expose on the sensor the same way.
Exposure becomes a little more complicated when you’re photographing larger areas of bright or dark tones. This is why large areas of white snow often turn out gray. In order for the snow to be record as white, you have to add some additional exposure, usually via your camera’s exposure-compensation feature, denoted by the +/- button on your camera. Exposure compensation is a method of fine-tuning the exposure of a scene by compensating for overly bright or dark areas.
It’s important to recognize when a particular subject could fool your camera’s meter, and how to meter for best results. Generally speaking, any time your predominant subject area is darker or lighter than a mid tone, the meter could be fooled into under or over-exposing your image.
Your camera’s exposure-compensation feature lets you add or subtract exposure from the metered exposure. This is done in one-third stop increments up to a maximum of three stops in either direction, depending on your DSLR. Once it’s set, this compensation will be applied to each frame until you set it back to zero. Knowing how much compensation to use is usually a matter of experience.
This is like having an insurance policy for your images. It’s similar to exposure compensation in that it changes the exposure to a pre-defined level, but when you set auto-exposure bracketing and you shoot an image, the camera will automatically shoot one (or more) at the metered setting, and one at the set amount of overexposure and one at the same amount of underexposure. To program auto-exposure bracketing, you just tell the camera how many frames you want to shoot and how many stops (or fractions of a stop) difference you want between each frame.
You’ll get three images (or perhaps more, depending on your camera), one with the as-metered exposure, then one underexposed by say, a ½-stop, and one overexposed by a ½-stop, depending on how you’ve set your camera. Later on, when you’re viewing these images on your computer, you can decide which exposure works best. Auto-exposure bracketing is a great tool for learning how various exposures will affect the same subject. Even when you have more experience, you can utilize it in very demanding lighting situations.