There's been something of a silent revolution in the world of digital photography in recent years. Digital cameras are amazing marvels of modern engineering not just because they dispense with film and capture their photos digitally, but also because they are far smarter than cameras were just 10 or 15 years ago. Today's digital cameras take better pictures, with much better exposure, than any pocket camera from the 80s or 90s.
Even so, no camera is perfect, and badly exposed photos are not uncommon. Thankfully, it's easy to evaluate the results and correct the camera's exposure on the fly. So, let's learn about the exposure compensation feature built into most digital cameras.
Adjusting Your Exposure
The exposure compensation control is frequently identified by the letters EV (which stand for Exposure Value) or a +/- symbol. The EV control lets you adjust the exposure up or down in small increments.
Your camera measures the light levels in the scene and tries to set the camera to what it thinks is the best exposure. But if you vary the EV level, you can force the camera to over- or underexpose the picture by a certain amount based on your own judgement. It's a great compromise, since the camera is still doing most of the work by measuring the overall exposure. You're just tweaking it a little.
Consider these stuffed animals, for instance. I focused on the penguin, which led the camera to overexpose the picture too much, blowing out the tiger. This bad exposure was apparent as soon as I reviewed the photo in the LCD.
Without changing anything else, I "dialled down" the exposure by setting the EV control to -1, which meant that I underexposed the photo by one stop – which resulted in a much better photo.
So what is this "stop" business? That's just a measure of how much light is getting into your camera. When you change the exposure by one stop upwards, you are doubling the amount of light in the scene, or halving it if you ratchet it down. Two stops upwards is four times the original amount of light, or a quarter if you move down. That's why your camera's EV control probably lets you adjust the exposure in small increments, such as 1/3 stop. That gives you finer control for more accurate lighting adjustment.
Try It Yourself
So now you know the basics. Take a photo and immediately inspect the results in your camera's LCD display. If your camera can display a histogram, be sure to turn that on so you can graphically see if the picture is under- or overexposed. If it is, dial in an EV adjustment and take a second shot.
When you get home, download your photos to the PC and compare the two pictures side-by-side so you can see how the EV control affected your exposure. Try a few times, and you'll start to get a sense for when exposure compensation is helpful, and how much you need to use.