Digital Focus: Choose the Right Exposure Mode

Feature: Choosing the Right Exposure Mode

Which is more neglected: the Maytag repairman or those exposure mode controls on your digital camera? At least the Maytag guy can complain to people on TV occasionally. For many folks, the exposure controls never even get a second thought.

If you leave your camera on its full-automatic setting all the time, this week's newsletter is for you. You'll get no argument from me that your camera's Auto setting is great ... at least half the time. There are many occasions, though, when a few tweaks could save the day, or at least give you a better picture.

Aperture Takes Priority

Many digital cameras come with a pair of exposure modes called Aperture Priority and Shutter Priority. These are great when you want to get a little creative.

Aperture Priority, often abbreviated with just the letter A on the camera's LCD menu or on a dial on top of the camera, is the mode to choose when you want direct control over how much of the image is in sharp focus, but you still want the camera to work in a mostly automated way. This control lets you dial in the aperture setting for your picture, and the camera itself calculates and sets the appropriate shutter speed to match.

When you set a big aperture value, like f/11 or f/16, you're maximizing the depth of field in the picture. The entire depth of the image, from the front to the back, will be in sharp focus. On the other hand, you can set a low f/stop, like f/2 or f/4, to minimize the depth of field. Only the subject will be in sharp focus, and the background will be comfortably blurred.

Why would you care about this? Depth of field mostly becomes an issue when shooting portraits, because the subject will stand out from the background better if it is the only thing in focus. The Aperture Priority setting can come in handy at other times, too. If you're taking a close-up photo, such as a shot of a bug on a leaf, you'll want to maximize your depth of field. Depth of field gets really shallow in macro-photography, so when you're engaged in taking pictures of small subjects like bugs, coins, jewelry, and flowers, you want to dial-in as much as you possibly can to keep your entire subject in sharp focus.

When Speed Counts

Shutter Priority (often abbreviated with an S) lets you change the other exposure variable. Using Shutter Priority, you can select any shutter speed from very fast to quite slow. Select a shutter speed, and the camera adjusts the aperture to match. Note that digital cameras tend to have maximum shutter speeds of up to 1/500 or 1/1000 of a second, and they can handle shutter speeds as low as 1, 2, or even 8 seconds--as long as the camera thinks the lighting is low enough to allow such long exposures.

The Shutter Priority mode is usually most helpful in motion photography. Want to freeze the action? Pick a very fast shutter speed; the faster the better. Want to show "motion blur" in action shots? Slow down the shutter speed.

Of course, you're astute enough to realize that since your camera's shutter speed and aperture setting are so closely related, both controls really do the same thing. So if your camera doesn't have an Aperture Priority control but it does have Shutter Priority, you can set the shutter speed high in order to reduce the depth of field and get a blurry background. If you have both controls, though, use whichever one gives you the most direct control over your subject. After all, these program modes are there for your convenience.

Taking Manual Control

If your camera has a manual exposure control, you'll probably never use it--and I wouldn't blame you. The automatic and priority modes are fine 99 percent of the time. In fact, there are very few situations in which manual control would come in handy.

The most common situation in which I switch to manual control is night photography. Auto-exposure controls aren't particularly useful at night; I often end up switching to manual and taking a long time-exposure with the aperture wide open. I'll give you details on how to do that in a future newsletter.