Shoot like a Pro

Controlling exposure

Written by Uncle Frank

Your digital camera is a technical marvel, but no matter how much of a beginner you are, it needs your help when it comes to setting the brightness level for certain kinds of scenes.

blackcatYour digital camera is a technical marvel, but no matter how much of a beginner you are, it needs your help when it comes to setting the brightness level for certain kinds of scenes.

It’s been “taught” that a typical image, with a mixture of bright and dark elements, should result in a picture of a specific average brightness, which is called the 18% gray standard. It usually works well, but if you have a composition with a lot of snow in it which should result in a very bright picture, your camera will be fooled into underexposing it, and the white snow will end up looking gray.

It works the other way, too. If you take a close-up of a black cat, your camera will overexpose the picture, and the kitty’s! fur will look gray.

To prove the point, I took a picture of a piece of a black foam core board, and a picture of a piece of a white foam core board. I set the aperture at f/3.4 each shot, so all the camera could vary was the time the shutter was open.

Here are the results.Can you guess which is which?

ev-samplesThey look almost identical. But if you compared the shooting data for these two pictures, you’d know the answer immediately. In order to “properly expose” the white board, the camera kept the shutter open for 1/6th of a second, while for the black board, it held the shutter open for 3.05 seconds. That’s how it maintained the 18% gray standard in both cases and that’s why it made both boards look unnaturally gray.

So how do we handle a snow scene, or a black cat portrait? Most digital cameras have a feature which lets us over-ride the camera’s rigid ideas about the correct average brightness level. It’s called exposure compensation (EC), and it lets the operator adjust the exposure value (ev) in steps of 1/3rd ev over a range of -2.0ev (very dark) to +2.0ev (very bright). So If your composition consists largely of very bright elements, try increasing EC by as much as +1.0ev to get a natural appearance. And if you’re taking a close-up of a black cat, you’ll probably have to decrease EC more than -1.0ev.

Don’t be afraid to experiment taking control over exposure levels. Your camera is smart, but it has no idea what the scene you’re photographing actually looks like, and its metering system can’t hold a candle to your eyes.

By the way, fcb sample #1 was the white board and sample #2 was black. Happy shooting!